Embedded linux system development (slides)

1. Embedded Linux system development Embedded Linux system development Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Latest update: October 20, 2014. Document updates and sources: http://free-electrons.com/doc/training/embedded-linux Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 1/526

2. Rights to copy © Copyright 2004-2014, Free Electrons License: Creative Commons Attribution - Share Alike 3.0 http://creativecommons.org/licenses/by-sa/3.0/legalcode You are free: I to copy, distribute, display, and perform the work I to make derivative works I to make commercial use of the work Under the following conditions: I Attribution. You must give the original author credit. I Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under a license identical to this one. I For any reuse or distribution, you must make clear to others the license terms of this work. I Any of these conditions can be waived if you get permission from the copyright holder. Your fair use and other rights are in no way aected by the above. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 2/526

3. Electronic copies of these documents I Electronic copies of your particular version of the materials are available on: http://free-electrons.com/doc/training/embedded-linux I Open the corresponding documents and use them throughout the course to look for explanations given earlier by the instructor. I You will need these electronic versions because we neither print any index nor any table of contents (quite high environmental cost for little added value) I For future reference, see the

4. rst slide to see where document updates will be available. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 3/526

5. Hyperlinks in the document There are many hyperlinks in the document I Regular hyperlinks: http://kernel.org/ I Kernel documentation links: Documentation/kmemcheck.txt I Links to kernel source

6. les and directories: drivers/input include/linux/fb.h I Links to the declarations, de

7. nitions and instances of kernel symbols (functions, types, data, structures): platform_get_irq() GFP_KERNEL struct file_operations Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 4/526

8. Free Electrons at a glance I Engineering company created in 2004 (not a training company!) I Locations: Orange, Toulouse, Lyon (France) I Serving customers all around the world See http://free-electrons.com/company/customers/ I Head count: 9 Only Free Software enthusiasts! I Focus: Embedded Linux, Linux kernel, Android Free Software / Open Source for embedded and real-time systems. I Activities: development, training, consulting, technical support. I Added value: get the best of the user and development community and the resources it oers. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 5/526

9. Free Electrons on-line resources I All our training materials: http://free-electrons.com/docs/ I Technical blog: http://free-electrons.com/blog/ I Quarterly newsletter: http://lists.free-electrons. com/mailman/listinfo/newsletter I News and discussions (Google +): https://plus.google.com/+FreeElectronsDevelopers I News and discussions (LinkedIn): http://linkedin.com/groups/Free-Electrons-4501089 I Quick news (Twitter): http://twitter.com/free_electrons I Linux Cross Reference - browse Linux kernel sources on-line: http://lxr.free-electrons.com Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 6/526

10. Mailing lists for session participants If you participated to a course taught by Free Electrons, you can subscribe to our mailing lists dedicated to our training customers: I To ask questions about the topics covered by the courses, and to get a

11. rst level of technical support for issues that your are facing in real life or with your own hardware. I To share your experience with other people having taken the same course and done the same practical labs. I To share further comments and suggestions about course contents. I To get news about important updates to the course materials. See http://free-electrons.com/training/mailing-lists A simple way to register:

12. ll the form on http://j.mp/1r1HhkZ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 7/526

13. Generic course information Generic course information Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 8/526

14. Hardware used in this training session Using Atmel SAMA5D3 Xplained boards in all practical labs I SAMA5D36 (Cortex A5) CPU from Atmel I USB powered! I 256 MB DDR2 RAM, 256 MB NAND ash I 2 Ethernet ports (Gigabit + 100 Mbit) I 2 USB 2.0 host, 1 USB device I 1 MMC/SD slot I 3.3 V serial port (like Beaglebone Black) I Misc: Arduino R3-compatible header, JTAG, buttons, LEDs I Currently sold at 69 EUR by Mouser (V.A.T. not included) Board and CPU documentation, design

15. les, software: http://www.atmel.com/sama5d3xplained Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 9/526

16. Participate! During the lectures... I Don't hesitate to ask questions. Other people in the audience may have similar questions too. I This helps the trainer to detect any explanation that wasn't clear or detailed enough. I Don't hesitate to share your experience, for example to compare Linux / Android with other operating systems used in your company. I Your point of view is most valuable, because it can be similar to your colleagues' and dierent from the trainer's. I Your participation can make our session more interactive and make the topics easier to learn. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 10/526

17. Practical lab guidelines During practical labs... I We cannot support more than 8 workstations at once (each with its board and equipment). Having more would make the whole class progress slower, compromising the coverage of the whole training agenda (exception for public sessions: up to 10 people). I So, if you are more than 8 participants, please form up to 8 working groups. I Open the electronic copy of your lecture materials, and use it throughout the practical labs to

18. nd the slides you need again. I Don't copy and paste from the PDF slides. The slides contain UTF-8 characters that look the same as ASCII ones, but won't be understood by shells or compilers. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 11/526

19. Cooperate! As in the Free Software and Open Source community, cooperation during practical labs is valuable in this training session: I If you complete your labs before other people, don't hesitate to help other people and investigate the issues they face. The faster we progress as a group, the more time we have to explore extra topics. I Explain what you understood to other participants when needed. It also helps to consolidate your knowledge. I Don't hesitate to report potential bugs to your instructor. I Don't hesitate to look for solutions on the Internet as well. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 12/526

20. Command memento sheet I This memento sheet gives command examples for the most typical needs (looking for

21. les, extracting a tar archive...) I It saves us 1 day of UNIX / Linux command line training. I Our best tip: in the command line shell, always hit the Tab key to complete command names and

22. le paths. This avoids 95% of typing mistakes. I Get an electronic copy on http://free-electrons.com/ doc/training/embedded-linux/ command_memento.pdf Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 13/526

23. vi basic commands I The vi editor is very useful to make quick changes to

24. les in an embedded target. I Though not very user friendly at

25. rst, vi is very powerful and its main 15 commands are easy to learn and are sucient for 99% of everyone's needs! I Get an electronic copy on http://free-electrons.com/ doc/training/embedded-linux/ vi_memento.pdf I You can also take the quick tutorial by running vimtutor. This is a worthy investment! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 14/526

26. Introduction to Embedded Linux Introduction to Embedded Linux Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 15/526

27. Birth of free software I 1983, Richard Stallman, GNU project and the free software concept. Beginning of the development of gcc, gdb, glibc and other important tools I 1991, Linus Torvalds, Linux kernel project, a Unix-like operating system kernel. Together with GNU software and many other open-source components: a completely free operating system, GNU/Linux I 1995, Linux is more and more popular on server systems I 2000, Linux is more and more popular on embedded systems I 2008, Linux is more and more popular on mobile devices I 2010, Linux is more and more popular on phones Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 16/526

28. Free software? I A program is considered free when its license oers to all its users the following four freedoms I Freedom to run the software for any purpose I Freedom to study the software and to change it I Freedom to redistribute copies I Freedom to distribute copies of modi

29. ed versions I These freedoms are granted for both commercial and non-commercial use I They imply the availability of source code, software can be modi

30. ed and distributed to customers I Good match for embedded systems! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 17/526

31. What is embedded Linux? Embedded Linux is the usage of the Linux kernel and various open-source components in embedded systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 18/526

32. Introduction to Embedded Linux Advantages of Linux and open-source for embedded systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 19/526

33. Re-using components I The key advantage of Linux and open-source in embedded systems is the ability to re-use components I The open-source ecosystem already provides many components for standard features, from hardware support to network protocols, going through multimedia, graphic, cryptographic libraries, etc. I As soon as a hardware device, or a protocol, or a feature is wide-spread enough, high chance of having open-source components that support it. I Allows to quickly design and develop complicated products, based on existing components. I No-one should re-develop yet another operating system kernel, TCP/IP stack, USB stack or another graphical toolkit library. I Allows to focus on the added value of your product. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 20/526

34. Low cost I Free software can be duplicated on as many devices as you want, free of charge. I If your embedded system uses only free software, you can reduce the cost of software licenses to zero. Even the development tools are free, unless you choose a commercial embedded Linux edition. I Allows to have a higher budget for the hardware or to increase the company's skills and knowledge Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 21/526

35. Full control I With open-source, you have the source code for all components in your system I Allows unlimited modi

36. cations, changes, tuning, debugging, optimization, for an unlimited period of time I Without lock-in or dependency from a third-party vendor I To be true, non open-source components must be avoided when the system is designed and developed I Allows to have full control over the software part of your system Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 22/526

37. Quality I Many open-source components are widely used, on millions of systems I Usually higher quality than what an in-house development can produce, or even proprietary vendors I Of course, not all open-source components are of good quality, but most of the widely-used ones are. I Allows to design your system with high-quality components at the foundations Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 23/526

38. Eases testing of new features I Open-source being freely available, it is easy to get a piece of software and evaluate it I Allows to easily study several options while making a choice I Much easier than purchasing and demonstration procedures needed with most proprietary products I Allows to easily explore new possibilities and solutions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 24/526

39. Community support I Open-source software components are developed by communities of developers and users I This community can provide a high-quality support: you can directly contact the main developers of the component you are using. The likelyhood of getting an answer doesn't depend what company you work for. I Often better than traditional support, but one needs to understand how the community works to properly use the community support possibilities I Allows to speed up the resolution of problems when developing your system Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 25/526

40. Taking part into the community I Possibility of taking part into the development community of some of the components used in the embedded systems: bug reporting, test of new versions or features, patches that

41. x bugs or add new features, etc. I Most of the time the open-source components are not the core value of the product: it's the interest of everybody to contribute back. I For the engineers: a very motivating way of being recognized outside the company, communication with others in the same

42. eld, opening of new possibilities, etc. I For the managers: motivation factor for engineers, allows the company to be recognized in the open-source community and therefore get support more easily and be more attractive to open-source developers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 26/526

43. Introduction to Embedded Linux A few examples of embedded systems running Linux Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 27/526

44. Personal routers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 28/526

45. Television Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 29/526

46. Point of sale terminal Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 30/526

47. Laser cutting machine Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 31/526

48. Viticulture machine Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 32/526

49. Introduction to Embedded Linux Embedded hardware for Linux systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 33/526

50. Processor and architecture (1) I The Linux kernel and most other architecture-dependent component support a wide range of 32 and 64 bits architectures I x86 and x86-64, as found on PC platforms, but also embedded systems (multimedia, industrial) I ARM, with hundreds of dierent SoC (multimedia, industrial) I PowerPC (mainly real-time, industrial applications) I MIPS (mainly networking applications) I SuperH (mainly set top box and multimedia applications) I Black

51. n (DSP architecture) I Microblaze (soft-core for Xilinx FPGA) I Cold

52. re, SCore, Tile, Xtensa, Cris, FRV, AVR32, M32R Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 34/526

53. Processor and architecture (2) I Both MMU and no-MMU architectures are supported, even though no-MMU architectures have a few limitations. I Linux is not designed for small microcontrollers. I Besides the toolchain, the bootloader and the kernel, all other components are generally architecture-independent Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 35/526

54. RAM and storage I RAM: a very basic Linux system can work within 8 MB of RAM, but a more realistic system will usually require at least 32 MB of RAM. Depends on the type and size of applications. I Storage: a very basic Linux system can work within 4 MB of storage, but usually more is needed. I Flash storage is supported, both NAND and NOR ash, with speci

56. lesystems I Block storage including SD/MMC cards and eMMC is supported I Not necessarily interesting to be too restrictive on the amount of RAM/storage: having exibility at this level allows to re-use as many existing components as possible. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 36/526

57. Communication I The Linux kernel has support for many common communication buses I I2C I SPI I CAN I 1-wire I SDIO I USB I And also extensive networking support I Ethernet, Wi

58. , Bluetooth, CAN, etc. I IPv4, IPv6, TCP, UDP, SCTP, DCCP, etc. I Firewalling, advanced routing, multicast Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 37/526

59. Types of hardware platforms I Evaluation platforms from the SoC vendor. Usually expensive, but many peripherals are built-in. Generally unsuitable for real products. I Component on Module, a small board with only CPU/RAM/ ash and a few other core components, with connectors to access all other peripherals. Can be used to build end products for small to medium quantities. I Community development platforms, a new trend to make a particular SoC popular and easily available. These are ready-to-use and low cost, but usually have less peripherals than evaluation platforms. To some extent, can also be used for real products. I Custom platform. Schematics for evaluation boards or development platforms are more and more commonly freely available, making it easier to develop custom platforms. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 38/526

60. Criteria for choosing the hardware I Make sure the hardware you plan to use is already supported by the Linux kernel, and has an open-source bootloader, especially the SoC you're targeting. I Having support in the ocial versions of the projects (kernel, bootloader) is a lot better: quality is better, and new versions are available. I Some SoC vendors and/or board vendors do not contribute their changes back to the mainline Linux kernel. Ask them to do so, or use another product if you can. A good measurement is to see the delta between their kernel and the ocial one. I Between properly supported hardware in the ocial Linux kernel and poorly-supported hardware, there will be huge dierences in development time and cost. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 39/526

61. Introduction to Embedded Linux Embedded Linux system architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 40/526

62. Global architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 41/526

63. Software components I Cross-compilation toolchain I Compiler that runs on the development machine, but generates code for the target I Bootloader I Started by the hardware, responsible for basic initialization, loading and executing the kernel I Linux Kernel I Contains the process and memory management, network stack, device drivers and provides services to user space applications I C library I The interface between the kernel and the user space applications I Libraries and applications I Third-party or in-house Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 42/526

64. Embedded Linux work Several distinct tasks are needed when deploying embedded Linux in a product: I Board Support Package development I A BSP contains a bootloader and kernel with the suitable device drivers for the targeted hardware I Purpose of our Kernel Development training I System integration I Integrate all the components, bootloader, kernel, third-party libraries and applications and in-house applications into a working system I Purpose of this training I Development of applications I Normal Linux applications, but using speci

65. cally chosen libraries Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 43/526

66. Embedded Linux development environment Embedded Linux development environment Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 44/526

67. Embedded Linux solutions I Two ways to switch to embedded Linux I Use solutions provided and supported by vendors like MontaVista, Wind River or TimeSys. These solutions come with their own development tools and environment. They use a mix of open-source components and proprietary tools. I Use community solutions. They are completely open, supported by the community. I In Free Electrons training sessions, we do not promote a particular vendor, and therefore use community solutions I However, knowing the concepts, switching to vendor solutions will be easy Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 45/526

68. OS for Linux development I We strongly recommend to use Linux as the desktop operating system to embedded Linux developers, for multiple reasons. I All community tools are developed and designed to run on Linux. Trying to use them on other operating systems (Windows, Mac OS X) will lead to trouble, and their usage on these systems is generally not supported by community developers. I As Linux also runs on the embedded device, all the knowledge gained from using Linux on the desktop will apply similarly to the embedded device. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 46/526

69. Desktop Linux distribution I Any good and suciently recent Linux desktop distribution can be used for the development workstation I Ubuntu, Debian, Fedora, openSUSE, Red Hat, etc. I We have chosen Ubuntu, as it is a widely used and easy to use desktop Linux distribution I The Ubuntu setup on the training laptops has intentionally been left untouched after the normal installation process. Learning embedded Linux is also about learning the tools needed on the development workstation! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 47/526

70. Linux root and non-root users I Linux is a multi-user operating system I The root user is the administrator, and it can do privileged operations such as: mounting

71. lesystems, con

72. guring the network, creating device

73. les, changing the system con

74. guration, installing or removing software I All other users are unprivileged, and cannot perform these administrator-level operations I On an Ubuntu system, it is not possible to log in as root, only as a normal user. I The system has been con

75. gured so that the user account created

76. rst is allowed to run privileged operations through a program called sudo. I Example: sudo mount /dev/sda2 /mnt/disk Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 48/526

77. Software packages I The distribution mechanism for software in GNU/Linux is dierent from the one in Windows I Linux distributions provides a central and coherent way of installing, updating and removing applications and libraries: packages I Packages contains the application or library

78. les, and associated meta-information, such as the version and the dependencies I .deb on Debian and Ubuntu, .rpm on Red Hat, Fedora, openSUSE I Packages are stored in repositories, usually on HTTP or FTP servers I You should only use packages from ocial repositories for your distribution, unless strictly required. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 49/526

79. Managing software packages (1) Instructions for Debian based GNU/Linux systems (Debian, Ubuntu...) I Package repositories are speci

80. ed in /etc/apt/sources.list I To update package repository lists: sudo apt-get update I To

81. nd the name of a package to install, the best is to use the search engine on http://packages.debian.org or on http://packages.ubuntu.com. You may also use: apt-cache search keyword Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 50/526

82. Managing software packages (2) I To install a given package: sudo apt-get install package I To remove a given package: sudo apt-get remove package I To install all available package updates: sudo apt-get dist-upgrade I Get information about a package: apt-cache show package I Graphical interfaces I Synaptic for GNOME I KPackageKit for KDE Further details on package management: http://www.debian.org/doc/manuals/apt-howto/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 51/526

83. Host vs. target I When doing embedded development, there is always a split between I The host, the development workstation, which is typically a powerful PC I The target, which is the embedded system under development I They are connected by various means: almost always a serial line for debugging purposes, frequently an Ethernet connection, sometimes a JTAG interface for low-level debugging Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 52/526

84. Serial line communication program I An essential tool for embedded development is a serial line communication program, like HyperTerminal in Windows. I There are multiple options available in Linux: Minicom, Picocom, Gtkterm, Putty, etc. I In this training session, we recommend using the simplest of them: picocom I Installation with sudo apt-get install picocom I Run with picocom -b BAUD_RATE /dev/SERIAL_DEVICE I Exit with Control-A Control-X I SERIAL_DEVICE is typically I ttyUSBx for USB to serial converters I ttySx for real serial ports Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 53/526

85. Command line tips I Using the command line is mandatory for many operations needed for embedded Linux development I It is a very powerful way of interacting with the system, with which you can save a lot of time. I Some useful tips I You can use several tabs in the Gnome Terminal I Remember that you can use relative paths (for example: ../../linux) in addition to absolute paths (for example: /home/user) I In a shell, hit [Control] [r], then a keyword, will search through the command history. Hit [Control] [r] again to search backwards in the history I You can copy/paste paths directly from the

86. le manager to the terminal by drag-and-drop. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 54/526

87. Practical lab - Training Setup Prepare your lab environment I Download the lab archive I Enforce correct permissions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 55/526

88. Cross-compiling toolchains Cross-compiling toolchains Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 56/526

89. Cross-compiling toolchains De

90. nition and Components Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 57/526

91. De

92. nition (1) I The usual development tools available on a GNU/Linux workstation is a native toolchain I This toolchain runs on your workstation and generates code for your workstation, usually x86 I For embedded system development, it is usually impossible or not interesting to use a native toolchain I The target is too restricted in terms of storage and/or memory I The target is very slow compared to your workstation I You may not want to install all development tools on your target. I Therefore, cross-compiling toolchains are generally used. They run on your workstation but generate code for your target. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 58/526

93. De

94. nition (2) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 59/526

95. Machines in build procedures I Three machines must be distinguished when discussing toolchain creation I The build machine, where the toolchain is built. I The host machine, where the toolchain will be executed. I The target machine, where the binaries created by the toolchain are executed. I Four common build types are possible for toolchains Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 60/526

96. Dierent toolchain build procedures Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 61/526

97. Components Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 62/526

98. Binutils I Binutils is a set of tools to generate and manipulate binaries for a given CPU architecture I as, the assembler, that generates binary code from assembler source code I ld, the linker I ar, ranlib, to generate .a archives, used for libraries I objdump, readelf, size, nm, strings, to inspect binaries. Very useful analysis tools! I strip, to strip useless parts of binaries in order to reduce their size I http://www.gnu.org/software/binutils/ I GPL license Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 63/526

99. Kernel headers (1) I The C library and compiled programs needs to interact with the kernel I Available system calls and their numbers I Constant de

100. nitions I Data structures, etc. I Therefore, compiling the C library requires kernel headers, and many applications also require them. I Available in linux/... and asm/... and a few other directories corresponding to the ones visible in include/ in the kernel sources Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 64/526

101. Kernel headers (2) I System call numbers, in asm/unistd.h #define __NR_exit 1 #define __NR_fork 2 #define __NR_read 3 I Constant de

102. nitions, here in asm-generic/fcntl.h, included from asm/fcntl.h, included from linux/fcntl.h #define O_RDWR 00000002 I Data structures, here in asm/stat.h struct stat { unsigned long st_dev; unsigned long st_ino; [...] }; Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 65/526

103. Kernel headers (3) I The kernel to user space ABI is backward compatible I Binaries generated with a toolchain using kernel headers older than the running kernel will work without problem, but won't be able to use the new system calls, data structures, etc. I Binaries generated with a toolchain using kernel headers newer than the running kernel might work on if they don't use the recent features, otherwise they will break I Using the latest kernel headers is not necessary, unless access to the new kernel features is needed I The kernel headers are extracted from the kernel sources using the headers_install kernel Make

104. le target. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 66/526

105. GCC I GNU Compiler Collection, the famous free software compiler I Can compile C, C++, Ada, Fortran, Java, Objective-C, Objective-C++, and generate code for a large number of CPU architectures, including ARM, AVR, Black

106. n, CRIS, FRV, M32, MIPS, MN10300, PowerPC, SH, v850, i386, x86 64, IA64, Xtensa, etc. I http://gcc.gnu.org/ I Available under the GPL license, libraries under the LGPL. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 67/526

107. C library I The C library is an essential component of a Linux system I Interface between the applications and the kernel I Provides the well-known standard C API to ease application development I Several C libraries are available: glibc, uClibc, eglibc, dietlibc, newlib, etc. I The choice of the C library must be made at the time of the cross-compiling toolchain generation, as the GCC compiler is compiled against a speci

108. c C library. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 68/526

109. Cross-compiling toolchains C Libraries Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 69/526

110. glibc I License: LGPL I C library from the GNU project I Designed for performance, standards compliance and portability I Found on all GNU / Linux host systems I Of course, actively maintained I Quite big for small embedded systems: approx 2.5 MB on ARM (version 2.9 - libc: 1.5 MB, libm: 750 KB) I http://www.gnu.org/software/libc/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 70/526

111. uClibc I License: LGPL I Lightweight C library for small embedded systems I High con

112. gurability: many features can be enabled or disabled through a menucon

113. g interface I Works only with Linux/uClinux, works on most embedded architectures I No guaranteed binary compatibility. May need to recompile applications when the library con

114. guration changes. I Focus on size rather than performance I Small compile time I http://www.uclibc.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 71/526

115. uClibc (2) I Most of the applications compile with uClibc. This applies to all applications used in embedded systems. I Size (arm): 4 times smaller than glibc! I uClibc 0.9.30.1: approx. 600 KB (libuClibc: 460 KB, libm: 96KB) I glibc 2.9: approx 2.5 MB I Some features not available or limited: priority-inheritance mutexes, NPTL support is very new,

116. xed Name Service Switch functionality, etc. I Used on a large number of production embedded products, including consumer electronic devices I Supported by all commercial embedded Linux providers (proof of maturity). I Warning: though some development is still happening, the maintainers have stopped making releases since May 2012. The project is in trouble. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 72/526

117. eglibc I Embedded glibc, LGPL license too I Was a variant of glibc, better adapted to the needs of embedded systems, because of past disagreement with glibc maintainers. I eglibc's goals included reduced footprint, con

118. gurable components, better support for cross-compilation and cross-testing. I Could be built without support for NIS, locales, IPv6, and many other features. I Fortunately for eglibc, the glibc maintainer has changed and its features are now included in glibc. Version 2.19 (Feb. 2014) was the last release. I http: //en.wikipedia.org/wiki/Embedded_GLIBC Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 73/526

119. Honey, I shrunk the programs! I Executable size comparison on ARM, tested with eglibc 2.15 and uClibc 0.9.33.2 I Plain hello world program (stripped): helloworld static dynamic uClibc 18kB 2.5kB uClibc with Thumb-2 14kB 2.4kB eglibc with Thumb-2 361kB 2.7kB I Busybox (stripped): busybox static dynamic uClibc 750kB 603kB uClibc with Thumb-2 533kB 439kB eglibc with Thumb-2 934kB 444kB Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 74/526

120. Other smaller C libraries I Several other smaller C libraries have been developed, but none of them have the goal of allowing the compilation of large existing applications I They need specially written programs and applications I Choices: I Dietlibc, http://www.fefe.de/dietlibc/. Approximately 70 KB. I Newlib, http://sourceware.org/newlib/ I Klibc, http://www.kernel.org/pub/linux/libs/klibc/, designed for use in an initramfs or initrd at boot time. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 75/526

121. Cross-compiling toolchains Toolchain Options Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 76/526

122. ABI I When building a toolchain, the ABI used to generate binaries needs to be de

123. ned I ABI, for Application Binary Interface, de

124. nes the calling conventions (how function arguments are passed, how the return value is passed, how system calls are made) and the organization of structures (alignment, etc.) I All binaries in a system must be compiled with the same ABI, and the kernel must understand this ABI. I On ARM, two main ABIs: OABI and EABI I Nowadays everybody uses EABI I On MIPS, several ABIs: o32, o64, n32, n64 I http://en.wikipedia.org/wiki/Application_Binary_ Interface Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 77/526

125. Floating point support I Some processors have a oating point unit, some others do not. I For example, many ARMv4 and ARMv5 CPUs do not have a oating point unit. Since ARMv7, a VFP unit is mandatory. I For processors having a oating point unit, the toolchain should generate hard oat code, in order to use the oating point instructions directly I For processors without a oating point unit, two solutions I Generate hard oat code and rely on the kernel to emulate the oating point instructions. This is very slow. I Generate soft oat code, so that instead of generating oating point instructions, calls to a user space library are generated I Decision taken at toolchain con

126. guration time I Also possible to con

127. gure which oating point unit should be used Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 78/526

128. CPU optimization ags I A set of cross-compiling tools is speci

129. c to a CPU architecture (ARM, x86, MIPS, PowerPC) I However, with the -march=, -mcpu=, -mtune= options, one can select more precisely the target CPU type I For example, -march=armv7 -mcpu=cortex-a8 I At the toolchain compilation time, values can be chosen. They are used: I As the default values for the cross-compiling tools, when no other -march, -mcpu, -mtune options are passed I To compile the C library I Even if the C library has been compiled for armv5t, it doesn't prevent from compiling other programs for armv7 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 79/526

130. Cross-compiling toolchains Obtaining a Toolchain Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 80/526

131. Building a toolchain manually Building a cross-compiling toolchain by yourself is a dicult and painful task! Can take days or weeks! I Lots of details to learn: many components to build, complicated con

132. guration I Lots of decisions to make (such as C library version, ABI, oating point mechanisms, component versions) I Need kernel headers and C library sources I Need to be familiar with current gcc issues and patches on your platform I Useful to be familiar with building and con

133. guring tools I See the Crosstool-NG docs/ directory for details on how toolchains are built. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 81/526

134. Get a pre-compiled toolchain I Solution that many people choose I Advantage: it is the simplest and most convenient solution I Drawback: you can't

135. ne tune the toolchain to your needs I Determine what toolchain you need: CPU, endianism, C library, component versions, ABI, soft oat or hard oat, etc. I Check whether the available toolchains match your requirements. I Possible choices I Sourcery CodeBench toolchains I Linaro toolchains I More references at http://elinux.org/Toolchains Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 82/526

136. Sourcery CodeBench I CodeSourcery was a company with an extended expertise on free software toolchains: gcc, gdb, binutils and glibc. It has been bought by Mentor Graphics, which continues to provide similar services and products I They sell toolchains with support, but they also provide a Lite version, which is free and usable for commercial products I They have toolchains available for I ARM I MIPS I PowerPC I SuperH I x86 I Be sure to use the GNU/Linux versions. The EABI versions are for bare-metal development (no operating system) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 83/526

137. Linaro toolchains I Linaro contributes to improving mainline gcc on ARM, in particular by hiring CodeSourcery developers. I For people who can't wait for the next releases of gcc, Linaro releases modi

138. ed sources of stable releases of gcc, with these optimizations for ARM (mainly for recent Cortex A CPUs). I As any gcc release, these sources can be used by build tools to build their own binary toolchains (Buildroot, OpenEmbedded...) This allows to support glibc, uClibc and eglibc. I https://wiki.linaro.org/WorkingGroups/ToolChain I Binary packages are available for Ubuntu users, https://launchpad.net/~linaro-maintainers/+ archive/toolchain Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 84/526

139. Installing and using a pre-compiled toolchain I Follow the installation procedure proposed by the vendor I Usually, it is simply a matter of extracting a tarball wherever you want. I Then, add the path to toolchain binaries in your PATH: export PATH=/path/to/toolchain/bin/:$PATH I Finally, compile your applications PREFIX-gcc -o foobar foobar.c I PREFIX depends on the toolchain con

140. guration, and allows to distinguish cross-compilation tools from native compilation utilities Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 85/526

141. Toolchain building utilities Another solution is to use utilities that automate the process of building the toolchain I Same advantage as the pre-compiled toolchains: you don't need to mess up with all the details of the build process I But also oers more exibility in terms of toolchain con

142. guration, component version selection, etc. I They also usually contain several patches that

143. x known issues with the dierent components on some architectures I Multiple tools with identical principle: shell scripts or Make

144. le that automatically fetch, extract, con

145. gure, compile and install the dierent components Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 86/526

146. Toolchain building utilities (2) I Crosstool-ng I Rewrite of the older Crosstool, with a menucon

147. g-like con

148. guration system I Feature-full: supports uClibc, glibc, eglibc, hard and soft oat, many architectures I Actively maintained I http://crosstool-ng.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 87/526

149. Toolchain building utilities (3) Many root

150. lesystem build systems also allow the construction of a cross-compiling toolchain I Buildroot I Make

151. le-based, has a Crosstool-NG back-end, maintained by the community I http://www.buildroot.net I PTXdist I Make

152. le-based, uClibc or glibc, maintained mainly by Pengutronix I http://pengutronix.de/software/ptxdist/ I OpenEmbedded / Yocto I A featureful, but more complicated build system I http://www.openembedded.org/ I https://www.yoctoproject.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 88/526

153. Crosstool-NG: installation and usage I Installation of Crosstool-NG can be done system-wide, or just locally in the source directory. For local installation: ./configure --enable-local make make install I Some sample con

154. gurations for various architectures are available in samples, they can be listed using ./ct-ng list-samples I To load a sample con

155. guration ./ct-ng sample-name I To adjust the con

156. guration ./ct-ng menuconfig I To build the toolchain ./ct-ng build Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 89/526

157. Toolchain contents I The cross compilation tool binaries, in bin/ I This directory can be added to your PATH to ease usage of the toolchain I One or several sysroot, each containing I The C library and related libraries, compiled for the target I The C library headers and kernel headers I There is one sysroot for each variant: toolchains can be multilib if they have several copies of the C library for dierent con

158. gurations (for example: ARMv4T, ARMv5T, etc.) I CodeSourcery ARM toolchain are multilib, the sysroots are in arm-none-linux-gnueabi/libc/, arm-none-linux-gnueabi/libc/armv4t/, arm-none-linux-gnueabi/libc/thumb2 I Crosstool-NG toolchains can be multilib too (still experimental), otherwise the sysroot is in arm-unknown-linux-uclibcgnueabi/sysroot Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 90/526

159. Practical lab - Using Crosstool-NG Time to build your toolchain I Con

160. gure Crosstool-NG I Run it to build your own cross-compiling toolchain Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 91/526

161. Bootloaders Bootloaders Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 92/526

162. Bootloaders Boot Sequence Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 93/526

163. Bootloaders I The bootloader is a piece of code responsible for I Basic hardware initialization I Loading of an application binary, usually an operating system kernel, from ash storage, from the network, or from another type of non-volatile storage. I Possibly decompression of the application binary I Execution of the application I Besides these basic functions, most bootloaders provide a shell with various commands implementing dierent operations. I Loading of data from storage or network, memory inspection, hardware diagnostics and testing, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 94/526

164. Bootloaders on x86 (1) I The x86 processors are typically bundled on a board with a non-volatile memory containing a program, the BIOS. I This program gets executed by the CPU after reset, and is responsible for basic hardware initialization and loading of a small piece of code from non-volatile storage. I This piece of code is usually the

165. rst 512 bytes of a storage device I This piece of code is usually a 1st stage bootloader, which will load the full bootloader itself. I The bootloader can then oer all its features. It typically understands

166. lesystem formats so that the kernel

167. le can be loaded directly from a normal

168. lesystem. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 95/526

169. Bootloaders on x86 (2) I GRUB, Grand Uni

170. ed Bootloader, the most powerful one. http://www.gnu.org/software/grub/ I Can read many

171. lesystem formats to load the kernel image and the con

172. guration, provides a powerful shell with various commands, can load kernel images over the network, etc. I See our dedicated presentation for details: http://free-electrons.com/docs/grub/ I Syslinux, for network and removable media booting (USB key, CD-ROM) http://www.kernel.org/pub/linux/utils/boot/syslinux/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 96/526

173. Booting on embedded CPUs: case 1 I When powered, the CPU starts executing code at a

174. xed address I There is no other booting mechanism provided by the CPU I The hardware design must ensure that a NOR ash chip is wired so that it is accessible at the address at which the CPU starts executing instructions I The

175. rst stage bootloader must be programmed at this address in the NOR I NOR is mandatory, because it allows random access, which NAND doesn't allow I Not very common anymore (unpractical, and requires NOR ash) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 97/526

176. Booting on embedded CPUs: case 2 I The CPU has an integrated boot code in ROM I BootROM on AT91 CPUs, ROM code on OMAP, etc. I Exact details are CPU-dependent I This boot code is able to load a

177. rst stage bootloader from a storage device into an internal SRAM (DRAM not initialized yet) I Storage device can typically be: MMC, NAND, SPI ash, UART, etc. I The

178. rst stage bootloader is I Limited in size due to hardware constraints (SRAM size) I Provided either by the CPU vendor or through community projects I This

179. rst stage bootloader must initialize DRAM and other hardware devices and load a second stage bootloader into RAM Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 98/526

180. Booting on ARM Atmel AT91 I RomBoot: tries to

181. nd a valid bootstrap image from various storage sources, and load it into SRAM (DRAM not initialized yet). Size limited to 4 KB. No user interaction possible in standard boot mode. I AT91Bootstrap: runs from SRAM. Initializes the DRAM, the NAND or SPI controller, and loads the secondary bootloader into RAM and starts it. No user interaction possible. I U-Boot: runs from RAM. Initializes some other hardware devices (network, USB, etc.). Loads the kernel image from storage or network to RAM and starts it. Shell with commands provided. I Linux Kernel: runs from RAM. Takes over the system completely (bootloaders no longer exists). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 99/526

182. Booting on ARM TI OMAP3 I ROM Code: tries to

183. nd a valid bootstrap image from various storage sources, and load it into SRAM or RAM (RAM can be initialized by ROM code through a con

184. guration header). Size limited to 64 KB. No user interaction possible. I X-Loader or U-Boot: runs from SRAM. Initializes the DRAM, the NAND or MMC controller, and loads the secondary bootloader into RAM and starts it. No user interaction possible. File called MLO. I U-Boot: runs from RAM. Initializes some other hardware devices (network, USB, etc.). Loads the kernel image from storage or network to RAM and starts it. Shell with commands provided. File called u-boot.bin or u-boot.img. I Linux Kernel: runs from RAM. Takes over the system completely (bootloaders no longer exists). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 100/526

185. Booting on Marvell SoC I ROM Code: tries to

186. nd a valid bootstrap image from various storage sources, and load it into RAM. The RAM con

187. guration is described in a CPU-speci

188. c header, prepended to the bootloader image. I U-Boot: runs from RAM. Initializes some other hardware devices (network, USB, etc.). Loads the kernel image from storage or network to RAM and starts it. Shell with commands provided. File called u-boot.kwb. I Linux Kernel: runs from RAM. Takes over the system completely (bootloaders no longer exists). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 101/526

189. Generic bootloaders for embedded CPUs I We will focus on the generic part, the main bootloader, oering the most important features. I There are several open-source generic bootloaders. Here are the most popular ones: I U-Boot, the universal bootloader by Denx The most used on ARM, also used on PPC, MIPS, x86, m68k, NIOS, etc. The de-facto standard nowadays. We will study it in detail. http://www.denx.de/wiki/U-Boot I Barebox, a new architecture-neutral bootloader, written as a successor of U-Boot. Better design, better code, active development, but doesn't yet have as much hardware support as U-Boot. http://www.barebox.org I There are also a lot of other open-source or proprietary bootloaders, often architecture-speci

190. c I RedBoot, Yaboot, PMON, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 102/526

191. Bootloaders The U-boot bootloader Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 103/526

192. U-Boot U-Boot is a typical free software project I License: GPLv2 (same as Linux) I Freely available at http://www.denx.de/wiki/U-Boot I Documentation available at http://www.denx.de/wiki/U-Boot/Documentation I The latest development source code is available in a Git repository: http://git.denx.de/?p=u-boot.git;a=summary I Development and discussions happen around an open mailing-list http://lists.denx.de/pipermail/u-boot/ I Since the end of 2008, it follows a

193. xed-interval release schedule. Every two months, a new version is released. Versions are named YYYY.MM. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 104/526

194. U-Boot con

195. guration I Get the source code from the website, and uncompress it I The include/configs/ directory contains one con

196. guration

197. le for each supported board I It de

198. nes the CPU type, the peripherals and their con

199. guration, the memory mapping, the U-Boot features that should be compiled in, etc. I It is a simple .h

200. le that sets C pre-processor constants. See the README

201. le for the documentation of these constants. This

202. le can also be adjusted to add or remove features from U-Boot (commands, etc.). I Assuming that your board is already supported by U-Boot, there should be one entry corresponding to your board in the boards.cfg

203. le. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 105/526

204. U-Boot con

205. guration

206. le excerpt /* CPU configuration */ #define CONFIG_ARMV7 1 #define CONFIG_OMAP 1 #define CONFIG_OMAP34XX 1 #define CONFIG_OMAP3430 1 #define CONFIG_OMAP3_IGEP0020 1 [...] /* Memory configuration */ #define CONFIG_NR_DRAM_BANKS 2 #define PHYS_SDRAM_1 OMAP34XX_SDRC_CS0 #define PHYS_SDRAM_1_SIZE (32 20) #define PHYS_SDRAM_2 OMAP34XX_SDRC_CS1 [...] /* USB configuration */ #define CONFIG_MUSB_UDC 1 #define CONFIG_USB_OMAP3 1 #define CONFIG_TWL4030_USB 1 [...] /* Available commands and features */ #define CONFIG_CMD_CACHE #define CONFIG_CMD_EXT2 #define CONFIG_CMD_FAT #define CONFIG_CMD_I2C #define CONFIG_CMD_MMC #define CONFIG_CMD_NAND #define CONFIG_CMD_NET #define CONFIG_CMD_DHCP #define CONFIG_CMD_PING #define CONFIG_CMD_NFS #define CONFIG_CMD_MTDPARTS [...] Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 106/526

207. Con

208. guring and compiling U-Boot I U-Boot must be con

209. gured before being compiled I make BOARDNAME_config I Where BOARDNAME is the name of the board, as visible in the boards.cfg

210. le (

211. rst column). I Make sure that the cross-compiler is available in PATH I Compile U-Boot, by specifying the cross-compiler pre

212. x. Example, if your cross-compiler executable is arm-linux-gcc: make CROSS_COMPILE=arm-linux- I The main result is a u-boot.bin

213. le, which is the U-Boot image. Depending on your speci

214. c platform, there may be other specialized images: u-boot.img, u-boot.kwb, MLO, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 107/526

215. Installing U-Boot I U-Boot must usually be installed in ash memory to be executed by the hardware. Depending on the hardware, the installation of U-Boot is done in a dierent way: I The CPU provides some kind of speci

216. c boot monitor with which you can communicate through serial port or USB using a speci

217. c protocol I The CPU boots

218. rst on removable media (MMC) before booting from

219. xed media (NAND). In this case, boot from MMC to re ash a new version I U-Boot is already installed, and can be used to ash a new version of U-Boot. However, be careful: if the new version of U-Boot doesn't work, the board is unusable I The board provides a JTAG interface, which allows to write to the ash memory remotely, without any system running on the board. It also allows to rescue a board if the bootloader doesn't work. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 108/526

220. U-boot prompt I Connect the target to the host through a serial console I Power-up the board. On the serial console, you will see something like: U-Boot 2013.04 (May 29 2013 - 10:30:21) OMAP36XX/37XX-GP ES1.2, CPU-OPP2, L3-165MHz, Max CPU Clock 1 Ghz IGEPv2 + LPDDR/NAND I2C: ready DRAM: 512 MiB NAND: 512 MiB MMC: OMAP SD/MMC: 0 Die ID #255000029ff800000168580212029011 Net: smc911x-0 U-Boot # I The U-Boot shell oers a set of commands. We will study the most important ones, see the documentation for a complete reference or the help command. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 109/526

221. Information commands Flash information (NOR and SPI ash) U-Boot flinfo DataFlash:AT45DB021 Nb pages: 1024 Page Size: 264 Size= 270336 bytes Logical address: 0xC0000000 Area 0: C0000000 to C0001FFF (RO) Bootstrap Area 1: C0002000 to C0003FFF Environment Area 2: C0004000 to C0041FFF (RO) U-Boot NAND ash information U-Boot nand info Device 0: nand0, sector size 128 KiB Page size 2048 b OOB size 64 b Erase size 131072 b Version details U-Boot version U-Boot 2013.04 (May 29 2013 - 10:30:21) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 110/526

222. Important commands (1) I The exact set of commands depends on the U-Boot con

223. guration I help and help command I boot, runs the default boot command, stored in bootcmd I bootm address, starts a kernel image loaded at the given address in RAM I ext2load, loads a

224. le from an ext2

225. lesystem to RAM I And also ext2ls to list

226. les, ext2info for information I fatload, loads a

227. le from a FAT

228. lesystem to RAM I And also fatls and fatinfo I tftp, loads a

229. le from the network to RAM I ping, to test the network Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 111/526

230. Important commands (2) I loadb, loads, loady, load a

231. le from the serial line to RAM I usb, to initialize and control the USB subsystem, mainly used for USB storage devices such as USB keys I mmc, to initialize and control the MMC subsystem, used for SD and microSD cards I nand, to erase, read and write contents to NAND ash I erase, protect, cp, to erase, modify protection and write to NOR ash I md, displays memory contents. Can be useful to check the contents loaded in memory, or to look at hardware registers. I mm, modi

232. es memory contents. Can be useful to modify directly hardware registers, for testing purposes. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 112/526

233. Environment variables commands (1) I U-Boot can be con

234. gured through environment variables, which aect the behavior of the dierent commands. I Environment variables are loaded from ash to RAM at U-Boot startup, can be modi

235. ed and saved back to ash for persistence I There is a dedicated location in ash (or in MMC storage) to store the U-Boot environment, de

236. ned in the board con

237. guration

238. le Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 113/526

239. Environment variables commands (2) Commands to manipulate environment variables: I printenv Shows all variables I printenv variable-name Shows the value of a variable I setenv variable-name variable-value Changes the value of a variable, only in RAM I editenv variable-name Edits the value of a variable, only in RAM I saveenv Saves the current state of the environment to ash Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 114/526

240. Environment variables commands - Example u-boot # printenv baudrate=19200 ethaddr=00:40:95:36:35:33 netmask=255.255.255.0 ipaddr=10.0.0.11 serverip=10.0.0.1 stdin=serial stdout=serial stderr=serial u-boot # printenv serverip serverip=10.0.0.1 u-boot # setenv serverip 10.0.0.100 u-boot # saveenv Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 115/526

241. Important U-Boot env variables I bootcmd, contains the command that U-Boot will automatically execute at boot time after a con

242. gurable delay, if the process is not interrupted I bootargs, contains the arguments passed to the Linux kernel, covered later I serverip, the IP address of the server that U-Boot will contact for network related commands I ipaddr, the IP address that U-Boot will use I netmask, the network mask to contact the server I ethaddr, the MAC address, can only be set once I bootdelay, the delay in seconds before which U-Boot runs bootcmd I autostart, if yes, U-Boot starts automatically an image that has been loaded into memory Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 116/526

243. Scripts in environment variables I Environment variables can contain small scripts, to execute several commands and test the results of commands. I Useful to automate booting or upgrade processes I Several commands can be chained using the ; operator I Tests can be done using if command ; then ... ; else ... ; fi I Scripts are executed using run variable-name I You can reference other variables using ${variable-name} I Example I setenv mmc-boot 'if fatload mmc 0 80000000 boot. ini; then source; else if fatload mmc 0 80000000 uImage; then run mmc-bootargs; bootm; fi; fi' Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 117/526

244. Transferring

245. les to the target I U-Boot is mostly used to load and boot a kernel image, but it also allows to change the kernel image and the root

246. lesystem stored in ash. I Files must be exchanged between the target and the development workstation. This is possible: I Through the network if the target has an Ethernet connection, and U-Boot contains a driver for the Ethernet chip. This is the fastest and most ecient solution. I Through a USB key, if U-Boot supports the USB controller of your platform I Through a SD or microSD card, if U-Boot supports the MMC controller of your platform I Through the serial port Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 118/526

247. TFTP I Network transfer from the development workstation and U-Boot on the target takes place through TFTP I Trivial File Transfer Protocol I Somewhat similar to FTP, but without authentication and over UDP I A TFTP server is needed on the development workstation I sudo apt-get install tftpd-hpa I All

248. les in /var/lib/tftpboot are then visible through TFTP I A TFTP client is available in the tftp-hpa package, for testing I A TFTP client is integrated into U-Boot I Con

249. gure the ipaddr and serverip environment variables I Use tftp address filename to load a

251. U-boot mkimage I The kernel image that U-Boot loads and boots must be prepared, so that a U-Boot speci

252. c header is added in front of the image I This header gives details such as the image size, the expected load address, the compression type, etc. I This is done with a tool that comes in U-Boot, mkimage I Debian / Ubuntu: just install the u-boot-tools package. I Or, compile it by yourself: simply con

253. gure U-Boot for any board of any architecture and compile it. Then install mkimage: cp tools/mkimage /usr/local/bin/ I The special target uImage of the kernel Make

254. le can then be used to generate a kernel image suitable for U-Boot. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 120/526

255. Practical lab - U-Boot Time to start the practical lab! I Communicate with the board using a serial console I Con

256. gure, build and install U-Boot I Learn U-Boot commands I Set up TFTP communication with the board Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 121/526

257. Linux kernel introduction Linux kernel introduction Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 122/526

258. Linux kernel introduction Linux features Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 123/526

259. History I The Linux kernel is one component of a system, which also requires libraries and applications to provide features to end users. I The Linux kernel was created as a hobby in 1991 by a Finnish student, Linus Torvalds. I Linux quickly started to be used as the kernel for free software operating systems I Linus Torvalds has been able to create a large and dynamic developer and user community around Linux. I Nowadays, more than one thousand people contribute to each kernel release, individuals or companies big and small. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 124/526

260. Linux kernel key features I Portability and hardware support. Runs on most architectures. I Scalability. Can run on super computers as well as on tiny devices (4 MB of RAM is enough). I Compliance to standards and interoperability. I Exhaustive networking support. I Security. It can't hide its aws. Its code is reviewed by many experts. I Stability and reliability. I Modularity. Can include only what a system needs even at run time. I Easy to program. You can learn from existing code. Many useful resources on the net. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 125/526

261. Linux kernel in the system Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 126/526

262. Linux kernel main roles I Manage all the hardware resources: CPU, memory, I/O. I Provide a set of portable, architecture and hardware independent APIs to allow user space applications and libraries to use the hardware resources. I Handle concurrent accesses and usage of hardware resources from dierent applications. I Example: a single network interface is used by multiple user space applications through various network connections. The kernel is responsible to multiplex the hardware resource. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 127/526

263. System calls I The main interface between the kernel and user space is the set of system calls I About 300 system calls that provide the main kernel services I File and device operations, networking operations, inter-process communication, process management, memory mapping, timers, threads, synchronization primitives, etc. I This interface is stable over time: only new system calls can be added by the kernel developers I This system call interface is wrapped by the C library, and user space applications usually never make a system call directly but rather use the corresponding C library function Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 128/526

264. Pseudo

265. lesystems I Linux makes system and kernel information available in user space through pseudo

266. lesystems, sometimes also called virtual

267. lesystems I Pseudo

268. lesystems allow applications to see directories and

269. les that do not exist on any real storage: they are created and updated on the y by the kernel I The two most important pseudo

270. lesystems are I proc, usually mounted on /proc: Operating system related information (processes, memory management parameters...) I sysfs, usually mounted on /sys: Representation of the system as a set of devices and buses. Information about these devices. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 129/526

271. Inside the Linux kernel Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 130/526

272. Linux license I The whole Linux sources are Free Software released under the GNU General Public License version 2 (GPL v2). I For the Linux kernel, this basically implies that: I When you receive or buy a device with Linux on it, you should receive the Linux sources, with the right to study, modify and redistribute them. I When you produce Linux based devices, you must release the sources to the recipient, with the same rights, with no restriction. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 131/526

273. Supported hardware architectures I See the arch/ directory in the kernel sources I Minimum: 32 bit processors, with or without MMU, and gcc support I 32 bit architectures (arch/ subdirectories) Examples: arm, avr32, blackfin, c6x, m68k, microblaze, mips, score, sparc, um I 64 bit architectures: Examples: alpha, arm64, ia64, tile I 32/64 bit architectures Examples: powerpc, x86, sh, sparc I Find details in kernel sources: arch/arch/Kconfig, arch/arch/README, or Documentation/arch/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 132/526

274. Linux kernel introduction Linux versioning scheme and development process Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 133/526

275. Until 2.6 (1) I One stable major branch every 2 or 3 years I Identi

276. ed by an even middle number I Examples: 1.0.x, 2.0.x, 2.2.x, 2.4.x I One development branch to integrate new functionalities and major changes I Identi

277. ed by an odd middle number I Examples: 2.1.x, 2.3.x, 2.5.x I After some time, a development version becomes the new base version for the stable branch I Minor releases once in while: 2.2.23, 2.5.12, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 134/526

278. Until 2.6 (2) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 135/526

279. Changes since Linux 2.6 I Since 2.6.0, kernel developers have been able to introduce lots of new features one by one on a steady pace, without having to make disruptive changes to existing subsystems. I Since then, there has been no need to create a new development branch massively breaking compatibility with the stable branch. I Thanks to this, more features are released to users at a faster pace. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 136/526

280. 3.x stable branch I From 2003 to 2011, the ocial kernel versions were named 2.6.x. I Linux 3.0 was released in July 2011 I This is only a change to the numbering scheme I Ocial kernel versions are now named 3.x (3.0, 3.1, 3.2, etc.) I Stabilized versions are named 3.x.y (3.0.2, 3.4.3, etc.) I It eectively only removes a digit compared to the previous numbering scheme Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 137/526

281. New development model Using merge and bug

282. xing windows Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 138/526

283. New development model - Details I After the release of a 3.x version (for example), a two-weeks merge window opens, during which major additions are merged. I The merge window is closed by the release of test version 3.(x+1)-rc1 I The bug

284. xing period opens, for 6 to 10 weeks. I At regular intervals during the bug

285. xing period, 3.(x+1)-rcY test versions are released. I When considered suciently stable, kernel 3.(x+1) is released, and the process starts again. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 139/526

286. More stability for the kernel source tree I Issue: bug and security

287. xes only released for most recent stable kernel versions. I Some people need to have a recent kernel, but with long term support for security updates. I You could get long term support from a commercial embedded Linux provider. I You could reuse sources for the kernel used in Ubuntu Long Term Support releases (5 years of free security updates). I The http://kernel.org front page shows which versions will be supported for some time (up to 2 or 3 years), and which ones won't be supported any more (EOL: End Of Life) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 140/526

288. What's new in each Linux release? I The ocial list of changes for each Linux release is just a huge list of individual patches! commit aa6e52a35d388e730f4df0ec2ec48294590cc459 Author: Thomas Petazzoni [email protected] Date: Wed Jul 13 11:29:17 2011 +0200 at91: at91-ohci: support overcurrent notification Several USB power switches (AIC1526 or MIC2026) have a digital output that is used to notify that an overcurrent situation is taking place. This digital outputs are typically connected to GPIO inputs of the processor and can be used to be notified of these overcurrent situations. Therefore, we add a new overcurrent_pin[] array in the at91_usbh_data structure so that boards can tell the AT91 OHCI driver which pins are used for the overcurrent notification, and an overcurrent_supported boolean to tell the driver whether overcurrent is supported or not. The code has been largely borrowed from ohci-da8xx.c and ohci-s3c2410.c. Signed-off-by: Thomas Petazzoni [email protected] Signed-off-by: Nicolas Ferre [email protected] I Very dicult to

289. nd out the key changes and to get the global picture out of individual changes. I Fortunately, there are some useful resources available I http://wiki.kernelnewbies.org/LinuxChanges I http://lwn.net I http://linuxfr.org, for French readers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 141/526

290. Linux kernel introduction Linux kernel sources Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 142/526

291. Location of kernel sources I The ocial versions of the Linux kernel, as released by Linus Torvalds, are available at http://www.kernel.org I These versions follow the development model of the kernel I However, they may not contain the latest development from a speci

292. c area yet. Some features in development might not be ready for mainline inclusion yet. I Many chip vendors supply their own kernel sources I Focusing on hardware support

293. rst I Can have a very important delta with mainline Linux I Useful only when mainline hasn't caught up yet. I Many kernel sub-communities maintain their own kernel, with usually newer but less stable features I Architecture communities (ARM, MIPS, PowerPC, etc.), device drivers communities (I2C, SPI, USB, PCI, network, etc.), other communities (real-time, etc.) I No ocial releases, only development trees are available. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 143/526

294. Getting Linux sources I The kernel sources are available from http://kernel.org/pub/linux/kernel as full tarballs (complete kernel sources) and patches (dierences between two kernel versions). I However, more and more people use the git version control system. Absolutely needed for kernel development! I Fetch the entire kernel sources and history git clone git://git.kernel.org/pub/scm/linux/ kernel/git/torvalds/linux.git I Create a branch that starts at a speci

295. c stable version git checkout -b name-of-branch v3.11 I Web interface available at http://git.kernel.org/cgit/ linux/kernel/git/torvalds/linux.git/tree/. I Read more about Git at http://git-scm.com/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 144/526

296. Linux kernel size (1) I Linux 3.10 sources: Raw size: 573 MB (43,000

297. les, approx 15,800,000 lines) gzip compressed tar archive: 105 MB bzip2 compressed tar archive: 83 MB (better) xz compressed tar archive: 69 MB (best) I Minimum Linux 3.17 compiled kernel size, booting on the ARM Versatile board (hard drive on PCI, ext2

298. lesystem, ELF executable support, framebuer console and input devices): 876 KB (compressed), 2.3 MB (raw) I Why are these sources so big? Because they include thousands of device drivers, many network protocols, support many architectures and

299. lesystems... I The Linux core (scheduler, memory management...) is pretty small! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 145/526

300. Linux kernel size (2) As of kernel version 3.10. I drivers/: 49.4% I arch/: 21.9% I fs/: 6.0% I include/: 4.7% I sound/: 4.4% I Documentation/: 4.0% I net/: 3.9% I firmware/: 1.0% I kernel/: 1.0% I tools/: 0.9% I scripts/: 0.5% I mm/: 0.5% I crypto/: 0.4% I security/: 0.4% I lib/: 0.4% I block/: 0.2% I ... Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 146/526

301. Getting Linux sources I Full tarballs I Contain the complete kernel sources: long to download and uncompress, but must be done at least once I Example: http://www.kernel.org/pub/linux/kernel/v3.x/linux- 3.10.9.tar.xz I Extract command: tar xf linux-3.10.9.tar.xz I Incremental patches between versions I It assumes you already have a base version and you apply the correct patches in the right order. Quick to download and apply I Examples: http://www.kernel.org/pub/linux/kernel/v3.x/patch-3.10.xz (3.9 to 3.10) http://www.kernel.org/pub/linux/kernel/v3.x/patch-3.10.9.xz (3.10 to 3.10.9) I All previous kernel versions are available in http://kernel.org/pub/linux/kernel/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 147/526

302. Patch I A patch is the dierence between two source trees I Computed with the diff tool, or with more elaborate version control systems I They are very common in the open-source community I Excerpt from a patch: diff -Nru a/Makefile b/Makefile --- a/Makefile 2005-03-04 09:27:15 -08:00 +++ b/Makefile 2005-03-04 09:27:15 -08:00 @@ -1,7 +1,7 @@ VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = 11 -EXTRAVERSION = +EXTRAVERSION = .1 NAME=Woozy Numbat # *DOCUMENTATION* Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 148/526

303. Contents of a patch I One section per modi

304. ed

305. le, starting with a header diff -Nru a/Makefile b/Makefile --- a/Makefile 2005-03-04 09:27:15 -08:00 +++ b/Makefile 2005-03-04 09:27:15 -08:00 I One sub-section per modi

306. ed part of the

307. le, starting with header with the aected line numbers @@ -1,7 +1,7 @@ I Three lines of context before the change VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = 11 I The change itself -EXTRAVERSION = +EXTRAVERSION = .1 I Three lines of context after the change NAME=Woozy Numbat # *DOCUMENTATION* Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 149/526

308. Using the patch command The patch command: I Takes the patch contents on its standard input I Applies the modi

309. cations described by the patch into the current directory patch usage examples: I patch -pn diff_file I cat diff_file | patch -pn I xzcat diff_file.xz | patch -pn I bzcat diff_file.bz2 | patch -pn I zcat diff_file.gz | patch -pn I Notes: I n: number of directory levels to skip in the

310. le paths I You can reverse apply a patch with the -R option I You can test a patch with --dry-run option Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 150/526

311. Applying a Linux patch I Two types of Linux patches: I Either to be applied to the previous stable version (from 3.x-1 to 3.x) I Or implementing

312. xes to the current stable version (from 3.x to 3.x.y) I Can be downloaded in gzip, bzip2 or xz (much smaller) compressed

313. les. I Always produced for n=1 (that's what everybody does... do it too!) I Need to run the patch command inside the kernel source directory I Linux patch command line example: cd linux-3.9 xzcat ../patch-3.10.xz | patch -p1 xzcat ../patch-3.10.9.xz | patch -p1 cd ..; mv linux-3.9 linux-3.10.9 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 151/526

314. Practical lab - Kernel sources Time to start the practical lab! I Get the Linux kernel sources I Apply patches Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 152/526

315. Linux kernel introduction Kernel con

316. guration Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 153/526

317. Kernel con

318. guration and build system I The kernel con

319. guration and build system is based on multiple Make

320. les I One only interacts with the main Makefile, present at the top directory of the kernel source tree I Interaction takes place I using the make tool, which parses the Make

321. le I through various targets, de

322. ning which action should be done (con

323. guration, compilation, installation, etc.). Run make help to see all available targets. I Example I cd linux-3.6.x/ I make target Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 154/526

324. Kernel con

325. guration (1) I The kernel contains thousands of device drivers,

326. lesystem drivers, network protocols and other con

327. gurable items I Thousands of options are available, that are used to selectively compile parts of the kernel source code I The kernel con

328. guration is the process of de

329. ning the set of options with which you want your kernel to be compiled I The set of options depends I On your hardware (for device drivers, etc.) I On the capabilities you would like to give to your kernel (network capabilities,

330. lesystems, real-time, etc.) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 155/526

331. Kernel con

332. guration (2) I The con

333. guration is stored in the .config

334. le at the root of kernel sources I Simple text

335. le, key=value style I As options have dependencies, typically never edited by hand, but through graphical or text interfaces: I make xconfig, make gconfig (graphical) I make menuconfig, make nconfig (text) I You can switch from one to another, they all load/save the same .config

336. le, and show the same set of options I To modify a kernel in a GNU/Linux distribution: the con

337. guration

338. les are usually released in /boot/, together with kernel images: /boot/config-3.2.0-31-generic Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 156/526

339. Kernel or module? I The kernel image is a single

340. le, resulting from the linking of all object

341. les that correspond to features enabled in the con

342. guration I This is the

343. le that gets loaded in memory by the bootloader I All included features are therefore available as soon as the kernel starts, at a time where no

344. lesystem exists I Some features (device drivers,

345. lesystems, etc.) can however be compiled as modules I These are plugins that can be loaded/unloaded dynamically to add/remove features to the kernel I Each module is stored as a separate

346. le in the

347. lesystem, and therefore access to a

348. lesystem is mandatory to use modules I This is not possible in the early boot procedure of the kernel, because no

349. lesystem is available Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 157/526

350. Kernel option types I There are dierent types of options I bool options, they are either I true (to include the feature in the kernel) or I false (to exclude the feature from the kernel) I tristate options, they are either I true (to include the feature in the kernel image) or I module (to include the feature as a kernel module) or I false (to exclude the feature) I int options, to specify integer values I hex options, to specify hexadecimal values I string options, to specify string values Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 158/526

351. Kernel option dependencies I There are dependencies between kernel options I For example, enabling a network driver requires the network stack to be enabled I Two types of dependencies I depends on dependencies. In this case, option A that depends on option B is not visible until option B is enabled I select dependencies. In this case, with option A depending on option B, when option A is enabled, option B is automatically enabled I make xconfig allows to see all options, even the ones that cannot be selected because of missing dependencies. In this case, they are displayed in gray Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 159/526

352. make xcon

353. g make xconfig I The most common graphical interface to con

354. gure the kernel. I Make sure you read help - introduction: useful options! I File browser: easier to load con

355. guration

356. les I Search interface to look for parameters I Required Debian / Ubuntu packages: libqt4-dev g++ (libqt3-mt-dev for older kernel releases) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 160/526

357. make xcon

358. g screenshot Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 161/526

359. make xcon

360. g search interface Looks for a keyword in the parameter name. Allows to select or unselect found parameters. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 162/526

361. Kernel con

362. guration options Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 163/526

363. Corresponding .con

364. g

365. le excerpt Options are grouped by sections and are pre

366. xed with CONFIG_. # # CD-ROM/DVD Filesystems # CONFIG_ISO9660_FS=m CONFIG_JOLIET=y CONFIG_ZISOFS=y CONFIG_UDF_FS=y CONFIG_UDF_NLS=y # # DOS/FAT/NT Filesystems # # CONFIG_MSDOS_FS is not set # CONFIG_VFAT_FS is not set CONFIG_NTFS_FS=m # CONFIG_NTFS_DEBUG is not set CONFIG_NTFS_RW=y Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 164/526

367. make gcon

368. g make gconfig I GTK based graphical con

369. guration interface. Functionality similar to that of make xconfig. I Just lacking a search functionality. I Required Debian packages: libglade2-dev Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 165/526

370. make menucon

371. g make menuconfig I Useful when no graphics are available. Pretty convenient too! I Same interface found in other tools: BusyBox, Buildroot... I Required Debian packages: libncurses-dev Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 166/526

372. make ncon

373. g make nconfig I A newer, similar text interface I More user friendly (for example, easier to access help information). I Required Debian packages: libncurses-dev Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 167/526

374. make oldcon

375. g make oldconfig I Needed very often! I Useful to upgrade a .config

376. le from an earlier kernel release I Issues warnings for con

377. guration parameters that no longer exist in the new kernel. I Asks for values for new parameters If you edit a .config

378. le by hand, it's strongly recommended to run make oldconfig afterwards! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 168/526

379. Undoing con

380. guration changes A frequent problem: I After changing several kernel con

381. guration settings, your kernel no longer works. I If you don't remember all the changes you made, you can get back to your previous con

382. guration: $ cp .config.old .config I All the con

383. guration interfaces of the kernel (xconfig, menuconfig, oldconfig...) keep this .config.old backup copy. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 169/526

384. Con

385. guration per architecture I The set of con

386. guration options is architecture dependent I Some con

387. guration options are very architecture-speci

388. c I Most of the con

389. guration options (global kernel options, network subsystem,

390. lesystems, most of the device drivers) are visible in all architectures. I By default, the kernel build system assumes that the kernel is being built for the host architecture, i.e. native compilation I The architecture is not de

391. ned inside the con

392. guration, but at a higher level I We will see later how to override this behaviour, to allow the con

393. guration of kernels for a dierent architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 170/526

394. Linux kernel introduction Compiling and installing the kernel for the host system Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 171/526

395. Kernel compilation I make I in the main kernel source directory I Remember to run multiple jobs in parallel if you have multiple CPU cores. Example: make -j 4 I No need to run as root! I Generates I vmlinux, the raw uncompressed kernel image, at the ELF format, useful for debugging purposes, but cannot be booted I arch/arch/boot/*Image, the

396. nal, usually compressed, kernel image that can be booted I bzImage for x86, zImage for ARM, vmImage.gz for Black

397. n, etc. I arch/arch/boot/dts/*.dtb, compiled Device Tree

398. les (on some architectures) I All kernel modules, spread over the kernel source tree, as .ko

399. les. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 172/526

400. Kernel installation I make install I Does the installation for the host system by default, so needs to be run as root. Generally not used when compiling for an embedded system, and it installs

401. les on the development workstation. I Installs I /boot/vmlinuz-version Compressed kernel image. Same as the one in arch/arch/boot I /boot/System.map-version Stores kernel symbol addresses I /boot/config-version Kernel con

402. guration for this version I Typically re-runs the bootloader con

403. guration utility to take the new kernel into account. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 173/526

404. Module installation I make modules_install I Does the installation for the host system by default, so needs to be run as root I Installs all modules in /lib/modules/version/ I kernel/ Module .ko (Kernel Object)

405. les, in the same directory structure as in the sources. I modules.alias Module aliases for module loading utilities. Example line: alias sound-service-?-0 snd_mixer_oss I modules.dep Module dependencies I modules.symbols Tells which module a given symbol belongs to. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 174/526

406. Kernel cleanup targets I Clean-up generated

407. les (to force re-compilation): make clean I Remove all generated

408. les. Needed when switching from one architecture to another. Caution: it also removes your .config

409. le! make mrproper I Also remove editor backup and patch reject

410. les (mainly to generate patches): make distclean Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 175/526

411. Linux kernel introduction Cross-compiling the kernel Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 176/526

412. Cross-compiling the kernel When you compile a Linux kernel for another CPU architecture I Much faster than compiling natively, when the target system is much slower than your GNU/Linux workstation. I Much easier as development tools for your GNU/Linux workstation are much easier to

413. nd. I To make the dierence with a native compiler, cross-compiler executables are pre

414. xed by the name of the target system, architecture and sometimes library. Examples: mips-linux-gcc, the pre

415. x is mips-linux-arm- linux-gnueabi-gcc, the pre

416. x is arm-linux-gnueabi- Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 177/526

417. Specifying cross-compilation (1) The CPU architecture and cross-compiler pre

418. x are de

419. ned through the ARCH and CROSS_COMPILE variables in the toplevel Make

420. le. I ARCH is the name of the architecture. It is de

421. ned by the name of the subdirectory in arch/ in the kernel sources I Example: arm if you want to compile a kernel for the arm architecture. I CROSS_COMPILE is the pre

422. x of the cross compilation tools I Example: arm-linux- if your compiler is arm-linux-gcc Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 178/526

423. Specifying cross-compilation (2) Two solutions to de

424. ne ARCH and CROSS_COMPILE: I Pass ARCH and CROSS_COMPILE on the make command line: make ARCH=arm CROSS_COMPILE=arm-linux- ... Drawback: it is easy to forget to pass these variables when you run any make command, causing your build and con

425. guration to be screwed up. I De

426. ne ARCH and CROSS_COMPILE as environment variables: export ARCH=arm export CROSS_COMPILE=arm-linux- Drawback: it only works inside the current shell or terminal. You could put these settings in a

427. le that you source every time you start working on the project. If you only work on a single architecture with always the same toolchain, you could even put these settings in your ~/.bashrc

428. le to make them permanent and visible from any terminal. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 179/526

429. Prede

430. ned con

431. guration

432. les I Default con

433. guration

434. les available, per board or per-CPU family I They are stored in arch/arch/configs/, and are just minimal .config

435. les I This is the most common way of con

436. guring a kernel for embedded platforms I Run make help to

437. nd if one is available for your platform I To load a default con

438. guration

439. le, just run make acme_defconfig I This will overwrite your existing .config

440. le! I To create your own default con

441. guration

442. le I make savedefconfig, to create a minimal con

443. guration

444. le I mv defconfig arch/arch/configs/myown_defconfig Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 180/526

445. Con

446. guring the kernel I After loading a default con

447. guration

448. le, you can adjust the con

449. guration to your needs with the normal xconfig, gconfig or menuconfig interfaces I You can also start the con

450. guration from scratch without loading a default con

451. guration

452. le I As the architecture is dierent from your host architecture I Some options will be dierent from the native con

453. guration (processor and architecture speci

454. c options, speci

455. c drivers, etc.) I Many options will be identical (

456. lesystems, network protocols, architecture-independent drivers, etc.) I Make sure you have the support for the right CPU, the right board and the right device drivers. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 181/526

457. Device Tree I Many embedded architectures have a lot of non-discoverable hardware. I Depending on the architecture, such hardware is either described using C code directly within the kernel, or using a special hardware description language in a Device Tree. I ARM, PowerPC, OpenRISC, ARC, Microblaze are examples of architectures using the Device Tree. I A Device Tree Source, written by kernel developers, is compiled into a binary Device Tree Blob, passed at boot time to the kernel. I There is one dierent Device Tree for each board/platform supported by the kernel, available in arch/arm/boot/dts/board.dtb. I The bootloader must load both the kernel image and the Device Tree Blob in memory before starting the kernel. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 182/526

458. Building and installing the kernel I Run make I Copy the

459. nal kernel image to the target storage I can be uImage, zImage, vmlinux, bzImage in arch/arch/boot I copying the Device Tree Blob might be necessary as well, they are available in arch/arch/boot/dts I make install is rarely used in embedded development, as the kernel image is a single

460. le, easy to handle I It is however possible to customize the make install behaviour in arch/arch/boot/install.sh I make modules_install is used even in embedded development, as it installs many modules and description

461. les I make INSTALL_MOD_PATH=dir/ modules_install I The INSTALL_MOD_PATH variable is needed to install the modules in the target root

462. lesystem instead of your host root

463. lesystem. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 183/526

464. Booting with U-Boot I Recent versions of U-Boot can boot the zImage binary. I Older versions require a special kernel image format: uImage I uImage is generated from zImage using the mkimage tool. It is done automatically by the kernel make uImage target. I On some ARM platforms, make uImage requires passing a LOADADDR environment variable, which indicates at which physical memory address the kernel will be executed. I In addition to the kernel image, U-Boot can also pass a Device Tree Blob to the kernel. I The typical boot process is therefore: 1. Load zImage or uImage at address X in memory 2. Load board.dtb at address Y in memory 3. Start the kernel with bootz X - Y or bootm X - Y The - in the middle indicates no initramfs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 184/526

465. Kernel command line I In addition to the compile time con

466. guration, the kernel behaviour can be adjusted with no recompilation using the kernel command line I The kernel command line is a string that de

467. nes various arguments to the kernel I It is very important for system con

468. guration I root= for the root

469. lesystem (covered later) I console= for the destination of kernel messages I Many more exist. The most important ones are documented in Documentation/kernel-parameters.txt in kernel sources. I This kernel command line is either I Passed by the bootloader. In U-Boot, the contents of the bootargs environment variable is automatically passed to the kernel I Built into the kernel, using the CONFIG_CMDLINE option. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 185/526

470. Practical lab - Kernel cross-compiling I Set up the cross-compiling environment I Con

471. gure the kernel Makefile accordingly I Cross-compile the kernel for an arm platform I On this platform, interact with the bootloader and boot your kernel Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 186/526

472. Linux kernel introduction Using kernel modules Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 187/526

473. Advantages of modules I Modules make it easy to develop drivers without rebooting: load, test, unload, rebuild, load... I Useful to keep the kernel image size to the minimum (essential in GNU/Linux distributions for PCs). I Also useful to reduce boot time: you don't spend time initializing devices and kernel features that you only need later. I Caution: once loaded, have full control and privileges in the system. No particular protection. That's why only the root user can load and unload modules. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 188/526

474. Module dependencies I Some kernel modules can depend on other modules, which need to be loaded

475. rst. I Example: the usb-storage module depends on the scsi_mod, libusual and usbcore modules. I Dependencies are described in /lib/modules/kernel-version/modules.dep This

476. le is generated when you run make modules_install. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 189/526

477. Kernel log When a new module is loaded, related information is available in the kernel log. I The kernel keeps its messages in a circular buer (so that it doesn't consume more memory with many messages) I Kernel log messages are available through the dmesg command (diagnostic message) I Kernel log messages are also displayed in the system console (console messages can be

478. ltered by level using the loglevel kernel parameter, or completely disabled with the quiet parameter). I Note that you can write to the kernel log from user space too: echo nDebug info /dev/kmsg Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 190/526

479. Module utilities (1) I modinfo module_name modinfo module_path.ko Gets information about a module: parameters, license, description and dependencies. Very useful before deciding to load a module or not. I sudo insmod module_path.ko Tries to load the given module. The full path to the module object

480. le must be given. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 191/526

481. Understanding module loading issues I When loading a module fails, insmod often doesn't give you enough details! I Details are often available in the kernel log. I Example: $ sudo insmod ./intr_monitor.ko insmod: error inserting ./intr_monitor.ko : -1 Device or resource busy $ dmesg [17549774.552000] Failed to register handler for irq channel 2 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 192/526

482. Module utilities (2) I sudo modprobe module_name Most common usage of modprobe: tries to load all the modules the given module depends on, and then this module. Lots of other options are available. modprobe automatically looks in /lib/modules/version/ for the object

483. le corresponding to the given module name. I lsmod Displays the list of loaded modules Compare its output with the contents of /proc/modules! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 193/526

484. Module utilities (3) I sudo rmmod module_name Tries to remove the given module. Will only be allowed if the module is no longer in use (for example, no more processes opening a device

485. le) I sudo modprobe -r module_name Tries to remove the given module and all dependent modules (which are no longer needed after removing the module) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 194/526

486. Passing parameters to modules I Find available parameters: modinfo snd-intel8x0m I Through insmod: sudo insmod ./snd-intel8x0m.ko index=-2 I Through modprobe: Set parameters in /etc/modprobe.conf or in any

487. le in /etc/modprobe.d/: options snd-intel8x0m index=-2 I Through the kernel command line, when the driver is built statically into the kernel: snd-intel8x0m.index=-2 I snd-intel8x0m is the driver name I index is the driver parameter name I -2 is the driver parameter value Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 195/526

488. Check module parameter values How to

489. nd the current values for the parameters of a loaded module? I Check /sys/module/name/parameters. I There is one

490. le per parameter, containing the parameter value. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 196/526

491. Useful reading Linux Kernel in a Nutshell, Dec 2006 I By Greg Kroah-Hartman, O'Reilly http://www.kroah.com/lkn/ I A good reference book and guide on con

492. guring, compiling and managing the Linux kernel sources. I Freely available on-line! Great companion to the printed book for easy electronic searches! Available as single PDF

493. le on http://free-electrons.com/ community/kernel/lkn/ I Our rating: 2 stars Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 197/526

494. Linux Root Filesystem Linux Root Filesystem Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 198/526

495. Linux Root Filesystem Principle and solutions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 199/526

496. Filesystems I Filesystems are used to organize data in directories and

497. les on storage devices or on the network. The directories and

498. les are organized as a hierarchy I In Unix systems, applications and users see a single global hierarchy of

499. les and directories, which can be composed of several

500. lesystems. I Filesystems are mounted in a speci

501. c location in this hierarchy of directories I When a

502. lesystem is mounted in a directory (called mount point), the contents of this directory re ects the contents of the storage device I When the

503. lesystem is unmounted, the mount point is empty again. I This allows applications to access

504. les and directories easily, regardless of their exact storage location Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 200/526

505. Filesystems (2) I Create a mount point, which is just a directory $ mkdir /mnt/usbkey I It is empty $ ls /mnt/usbkey $ I Mount a storage device in this mount point $ mount -t vfat /dev/sda1 /mnt/usbkey $ I You can access the contents of the USB key $ ls /mnt/usbkey docs prog.c picture.png movie.avi $ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 201/526

506. mount / umount I mount allows to mount

507. lesystems I mount -t type device mountpoint I type is the type of

508. lesystem I device is the storage device, or network location to mount I mountpoint is the directory where

509. les of the storage device or network location will be accessible I mount with no arguments shows the currently mounted

510. lesystems I umount allows to unmount

511. lesystems I This is needed before rebooting, or before unplugging a USB key, because the Linux kernel caches writes in memory to increase performance. umount makes sure that these writes are committed to the storage. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 202/526

512. Root

513. lesystem I A particular

514. lesystem is mounted at the root of the hierarchy, identi

515. ed by / I This

516. lesystem is called the root

517. lesystem I As mount and umount are programs, they are

518. les inside a

519. lesystem. I They are not accessible before mounting at least one

520. lesystem. I As the root

521. lesystem is the

522. rst mounted

523. lesystem, it cannot be mounted with the normal mount command I It is mounted directly by the kernel, according to the root= kernel option I When no root

524. lesystem is available, the kernel panics Please append a correct root= boot option Kernel panic - not syncing: VFS: Unable to mount root fs on unknown block(0,0) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 203/526

525. Location of the root

526. lesystem I It can be mounted from dierent locations I From the partition of a hard disk I From the partition of a USB key I From the partition of an SD card I From the partition of a NAND ash chip or similar type of storage device I From the network, using the NFS protocol I From memory, using a pre-loaded

527. lesystem (by the bootloader) I etc. I It is up to the system designer to choose the con

528. guration for the system, and con

529. gure the kernel behaviour with root= Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 204/526

530. Mounting rootfs from storage devices I Partitions of a hard disk or USB key I root=/dev/sdXY, where X is a letter indicating the device, and Y a number indicating the partition I /dev/sdb2 is the second partition of the second disk drive (either USB key or ATA hard drive) I Partitions of an SD card I root=/dev/mmcblkXpY, where X is a number indicating the device and Y a number indicating the partition I /dev/mmcblk0p2 is the second partition of the

531. rst device I Partitions of ash storage I root=/dev/mtdblockX, where X is the partition number I /dev/mtdblock3 is the fourth partition of a NAND ash chip (if only one NAND ash chip is present) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 205/526

532. Mounting rootfs over the network (1) Once networking works, your root

533. lesystem could be a directory on your GNU/Linux development host, exported by NFS (Network File System). This is very convenient for system development: I Makes it very easy to update

534. les on the root

535. lesystem, without rebooting. Much faster than through the serial port. I Can have a big root

536. lesystem even if you don't have support for internal or external storage yet. I The root

537. lesystem can be huge. You can even build native compiler tools and build all the tools you need on the target itself (better to cross-compile though). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 206/526

538. Mounting rootfs over the network (2) On the development workstation side, a NFS server is needed I Install an NFS server (example: Debian, Ubuntu) sudo apt-get install nfs-kernel-server I Add the exported directory to your /etc/exports

539. le: /home/tux/rootfs 192.168.1.111(rw,no_root_squash, no_subtree_check) I 192.168.1.111 is the client IP address I rw,no_root_squash,no_subtree_check are the NFS server options for this directory export. I Start or restart your NFS server (example: Debian, Ubuntu) sudo /etc/init.d/nfs-kernel-server restart Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 207/526

540. Mounting rootfs over the network (3) I On the target system I The kernel must be compiled with I CONFIG_NFS_FS=y (NFS support) I CONFIG_IP_PNP=y (con

541. gure IP at boot time) I CONFIG_ROOT_NFS=y (support for NFS as rootfs) I The kernel must be booted with the following parameters: I root=/dev/nfs (we want rootfs over NFS) I ip=192.168.1.111 (target IP address) I nfsroot=192.168.1.110:/home/tux/rootfs/ (NFS server details) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 208/526

542. Mounting rootfs over the network (4) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 209/526

543. rootfs in memory: initramfs (1) I It is also possible to have the root

544. lesystem integrated into the kernel image I It is therefore loaded into memory together with the kernel I This mechanism is called initramfs I It integrates a compressed archive of the

545. lesystem into the kernel image I Variant: the compressed archive can also be loaded separately by the bootloader. I It is useful for two cases I Fast booting of very small root

546. lesystems. As the

547. lesystem is completely loaded at boot time, application startup is very fast. I As an intermediate step before switching to a real root

548. lesystem, located on devices for which drivers not part of the kernel image are needed (storage drivers,

549. lesystem drivers, network drivers). This is always used on the kernel of desktop/server distributions to keep the kernel image size reasonable. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 210/526

550. rootfs in memory: initramfs (2) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 211/526

551. rootfs in memory: initramfs (3) I The contents of an initramfs are de

552. ned at the kernel con

553. guration level, with the CONFIG_INITRAMFS_SOURCE option I Can be the path to a directory containing the root

554. lesystem contents I Can be the path to a cpio archive I Can be a text

555. le describing the contents of the initramfs (see documentation for details) I The kernel build process will automatically take the contents of the CONFIG_INITRAMFS_SOURCE option and integrate the root

556. lesystem into the kernel image I Details (in kernel sources): Documentation/filesystems/ramfs-rootfs-initramfs.txt Documentation/early-userspace/README Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 212/526

557. Linux Root Filesystem Contents Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 213/526

558. Root

559. lesystem organization I The organization of a Linux root

560. lesystem in terms of directories is well-de

561. ned by the Filesystem Hierarchy Standard I http://www.linuxfoundation.org/collaborate/ workgroups/lsb/fhs I Most Linux systems conform to this speci

562. cation I Applications expect this organization I It makes it easier for developers and users as the

563. lesystem organization is similar in all systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 214/526

564. Important directories (1) /bin Basic programs /boot Kernel image (only when the kernel is loaded from a

565. lesystem, not common on non-x86 architectures) /dev Device

566. les (covered later) /etc System-wide con

567. guration /home Directory for the users home directories /lib Basic libraries /media Mount points for removable media /mnt Mount points for static media /proc Mount point for the proc virtual

568. lesystem Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 215/526

569. Important directories (2) /root Home directory of the root user /sbin Basic system programs /sys Mount point of the sysfs virtual

570. lesystem /tmp Temporary

571. les /usr /usr/bin Non-basic programs /usr/lib Non-basic libraries /usr/sbin Non-basic system programs /var Variable data

572. les. This includes spool directories and

573. les, administrative and logging data, and transient and temporary

574. les Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 216/526

575. Separation of programs and libraries I Basic programs are installed in /bin and /sbin and basic libraries in /lib I All other programs are installed in /usr/bin and /usr/sbin and all other libraries in /usr/lib I In the past, on Unix systems, /usr was very often mounted over the network, through NFS I In order to allow the system to boot when the network was down, some binaries and libraries are stored in /bin, /sbin and /lib I /bin and /sbin contain programs like ls, ifconfig, cp, bash, etc. I /lib contains the C library and sometimes a few other basic libraries I All other programs and libraries are in /usr Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 217/526

576. Linux Root Filesystem Device Files Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 218/526

577. Devices I One of the kernel important role is to allow applications to access hardware devices I In the Linux kernel, most devices are presented to user space applications through two dierent abstractions I Character device I Block device I Internally, the kernel identi

578. es each device by a triplet of information I Type (character or block) I Major (typically the category of device) I Minor (typically the identi

579. er of the device) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 219/526

580. Types of devices I Block devices I A device composed of

581. xed-sized blocks, that can be read and written to store data I Used for hard disks, USB keys, SD cards, etc. I Character devices I Originally, an in

582. nite stream of bytes, with no beginning, no end, no size. The pure example: a serial port. I Used for serial ports, terminals, but also sound cards, video acquisition devices, frame buers I Most of the devices that are not block devices are represented as character devices by the Linux kernel Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 220/526

583. Devices: everything is a

584. le I A very important Unix design decision was to represent most of the system objects as

585. les I It allows applications to manipulate all system objects with the normal

586. le API (open, read, write, close, etc.) I So, devices had to be represented as

587. les to the applications I This is done through a special artifact called a device

588. le I It is a special type of

589. le, that associates a

590. le name visible to user space applications to the triplet (type, major, minor) that the kernel understands I All device

591. les are by convention stored in the /dev directory Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 221/526

592. Device

593. les examples Example of device

594. les in a Linux system $ ls -l /dev/ttyS0 /dev/tty1 /dev/sda1 /dev/sda2 /dev/zero brw-rw---- 1 root disk 8, 1 2011-05-27 08:56 /dev/sda1 brw-rw---- 1 root disk 8, 2 2011-05-27 08:56 /dev/sda2 crw------- 1 root root 4, 1 2011-05-27 08:57 /dev/tty1 crw-rw---- 1 root dialout 4, 64 2011-05-27 08:56 /dev/ttyS0 crw-rw-rw- 1 root root 1, 5 2011-05-27 08:56 /dev/zero Example C code that uses the usual

595. le API to write data to a serial port int fd; fd = open(/dev/ttyS0, O_RDWR); write(fd, Hello, 5); close(fd); Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 222/526

596. Creating device

597. les I On a basic Linux system, the device

598. les have to be created manually using the mknod command I mknod /dev/device [c|b] major minor I Needs root privileges I Coherency between device

599. les and devices handled by the kernel is left to the system developer I On more elaborate Linux systems, mechanisms can be added to create/remove them automatically when devices appear and disappear I devtmpfs virtual

600. lesystem, since kernel 2.6.32 I udev daemon, solution used by desktop and server Linux systems I mdev program, a lighter solution than udev Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 223/526

601. Linux Root Filesystem Pseudo Filesystems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 224/526

602. proc virtual

603. lesystem I The proc virtual

604. lesystem exists since the beginning of Linux I It allows I The kernel to expose statistics about running processes in the system I The user to adjust at runtime various system parameters about process management, memory management, etc. I The proc

605. lesystem is used by many standard user space applications, and they expect it to be mounted in /proc I Applications such as ps or top would not work without the proc

606. lesystem I Command to mount /proc: mount -t proc nodev /proc I Documentation/filesystems/proc.txt in the kernel sources I man proc Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 225/526

607. proc contents I One directory for each running process in the system I /proc/pid I cat /proc/3840/cmdline I It contains details about the

608. les opened by the process, the CPU and memory usage, etc. I /proc/interrupts, /proc/devices, /proc/iomem, /proc/ioports contain general device-related information I /proc/cmdline contains the kernel command line I /proc/sys contains many

609. les that can be written to to adjust kernel parameters I They are called sysctl. See Documentation/sysctl/ in kernel sources. I Example echo 3 /proc/sys/vm/drop_caches Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 226/526

610. sysfs

611. lesystem I The sysfs

612. lesystem is a feature integrated in the 2.6 Linux kernel I It allows to represent in user space the vision that the kernel has of the buses, devices and drivers in the system I It is useful for various user space applications that need to list and query the available hardware, for example udev or mdev. I All applications using sysfs expect it to be mounted in the /sys directory I Command to mount /sys: mount -t sysfs nodev /sys I $ ls /sys/ block bus class dev devices firmware fs kernel module power Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 227/526

613. Linux Root Filesystem Minimal

614. lesystem Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 228/526

615. Basic applications I In order to work, a Linux system needs at least a few applications I An init application, which is the

616. rst user space application started by the kernel after mounting the root

617. lesystem I The kernel tries to run /sbin/init, /bin/init, /etc/init and /bin/sh. I In the case of an initramfs, it will only look for /init. Another path can be supplied by the rdinit kernel argument. I If none of them are found, the kernel panics and the boot process is stopped. I The init application is responsible for starting all other user space applications and services I Usually a shell, to allow a user to interact with the system I Basic Unix applications, to copy

618. les, move

619. les, list

620. les (commands like mv, cp, mkdir, cat, etc.) I These basic components have to be integrated into the root

621. lesystem to make it usable Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 229/526

622. Overall booting process Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 230/526

623. Overall booting process with initramfs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 231/526

624. Busybox Busybox Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 232/526

625. Why Busybox? I A Linux system needs a basic set of programs to work I An init program I A shell I Various basic utilities for

626. le manipulation and system con

627. guration I In normal Linux systems, these programs are provided by dierent projects I coreutils, bash, grep, sed, tar, wget, modutils, etc. are all dierent projects I A lot of dierent components to integrate I Components not designed with embedded systems constraints in mind: they are not very con

628. gurable and have a wide range of features I Busybox is an alternative solution, extremely common on embedded systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 233/526

629. General purpose toolbox: BusyBox I Rewrite of many useful Unix command line utilities I Integrated into a single project, which makes it easy to work with I Designed with embedded systems in mind: highly con

630. gurable, no unnecessary features I All the utilities are compiled into a single executable, /bin/busybox I Symbolic links to /bin/busybox are created for each application integrated into Busybox I For a fairly featureful con

631. guration, less than 500 KB (statically compiled with uClibc) or less than 1 MB (statically compiled with glibc). I http://www.busybox.net/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 234/526

632. BusyBox commands! Commands available in BusyBox 1.13 [, [[, addgroup, adduser, adjtimex, ar, arp, arping, ash, awk, basename, bbconfig, bbsh, brctl, bunzip2, busybox, bzcat, bzip2, cal, cat, catv, chat, chattr, chcon, chgrp, chmod, chown, chpasswd, chpst, chroot, chrt, chvt, cksum, clear, cmp, comm, cp, cpio, crond, crontab, cryptpw, cttyhack, cut, date, dc, dd, deallocvt, delgroup, deluser, depmod, devfsd, df, dhcprelay, diff, dirname, dmesg, dnsd, dos2unix, dpkg, dpkg_deb, du, dumpkmap, dumpleases, e2fsck, echo, ed, egrep, eject, env, envdir, envuidgid, ether_wake, expand, expr, fakeidentd, false, fbset, fbsplash, fdflush, fdformat, fdisk, fetchmail, fgrep, find, findfs, fold, free, freeramdisk, fsck, fsck_minix, ftpget, ftpput, fuser, getenforce, getopt, getsebool, getty, grep, gunzip, gzip, halt, hd, hdparm, head, hexdump, hostid, hostname, httpd, hush, hwclock, id, ifconfig, ifdown, ifenslave, ifup, inetd, init, inotifyd, insmod, install, ip, ipaddr, ipcalc, ipcrm, ipcs, iplink, iproute, iprule, iptunnel, kbd_mode, kill, killall, killall5, klogd, lash, last, length, less, linux32, linux64, linuxrc, ln, load_policy, loadfont, loadkmap, logger, login, logname, logread, losetup, lpd, lpq, lpr, ls, lsattr, lsmod, lzmacat, makedevs, man, matchpathcon, md5sum, mdev, mesg, microcom, mkdir, mke2fs, mkfifo, mkfs_minix, mknod, mkswap, mktemp, modprobe, more, mount, mountpoint, msh, mt, mv, nameif, nc, netstat, nice, nmeter, nohup, nslookup, od, openvt, parse, passwd, patch, pgrep, pidof, ping, ping6, pipe_progress, pivot_root, pkill, poweroff, printenv, printf, ps, pscan, pwd, raidautorun, rdate, rdev, readahead, readlink, readprofile, realpath, reboot, renice, reset, resize, restorecon, rm, rmdir, rmmod, route, rpm, rpm2cpio, rtcwake, run_parts, runcon, runlevel, runsv, runsvdir, rx, script, sed, selinuxenabled, sendmail, seq, sestatus, setarch, setconsole, setenforce, setfiles, setfont, setkeycodes, setlogcons, setsebool, setsid, setuidgid, sh, sha1sum, showkey, slattach, sleep, softlimit, sort, split, start_stop_daemon, stat, strings, stty, su, sulogin, sum, sv, svlogd, swapoff, swapon, switch_root, sync, sysctl, syslogd, tac, tail, tar, taskset, tcpsvd, tee, telnet, telnetd, test, tftp, tftpd, time, top, touch, tr, traceroute, true, tty, ttysize, tune2fs, udhcpc, udhcpd, udpsvd, umount, uname, uncompress, unexpand, uniq, unix2dos, unlzma, unzip, uptime, usleep, uudecode, uuencode, vconfig, vi, vlock, watch, watchdog, wc, wget, which, who, whoami, xargs, yes, zcat, zcip Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 235/526

633. Applet highlight: Busybox init I Busybox provides an implementation of an init program I Simpler than the init implementation found on desktop/server systems: no runlevels are implemented I A single con

634. guration

635. le: /etc/inittab I Each line has the form id::action:process I Allows to run services at startup, and to make sure that certain services are always running on the system I See examples/inittab in Busybox for details on the con

637. Applet highlight - BusyBox vi I If you are using BusyBox, adding vi support only adds 20K. (built with shared libraries, using uClibc). I You can select which exact features to compile in. I Users hardly realize that they are using a lightweight vi version! I Tip: you can learn vi on the desktop, by running the vimtutor command. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 237/526

638. Con

639. guring BusyBox I Get the latest stable sources from http://busybox.net I Con

640. gure BusyBox (creates a .config

641. le): I make defconfig Good to begin with BusyBox. Con

642. gures BusyBox with all options for regular users. I make allnoconfig Unselects all options. Good to con

643. gure only what you need. I make xconfig (graphical, needs the libqt3-mt-dev package) or make menuconfig (text) Same con

644. guration interfaces as the ones used by the Linux kernel (though older versions are used). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 238/526

645. BusyBox make xcon

646. g You can choose: I the commands to compile, I and even the command options and features that you need! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 239/526

647. Compiling BusyBox I Set the cross-compiler pre

648. x in the con

649. guration interface: BusyBox Settings - Build Options - Cross Compiler prefix Example: arm-linux- I Set the installation directory in the con

650. guration interface: BusyBox Settings - Installation Options - BusyBox installation prefix I Add the cross-compiler path to the PATH environment variable: export PATH=/usr/xtools/arm-unknown-linux-uclibcgnueabi/ bin:$PATH I Compile BusyBox: make I Install it (this creates a Unix directory structure symbolic links to the busybox executable): make install Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 240/526

651. Practical lab - A tiny embedded system I Make Linux boot on a directory on your workstation, shared by NFS I Create and con

652. gure a minimalistic Linux embedded system I Install and use BusyBox I System startup with /sbin/init I Setup a simple web interface I Use shared libraries Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 241/526

653. Block

654. lesystems Block

655. lesystems Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 242/526

656. Block vs. ash I Storage devices are classi

657. ed in two main types: block devices and ash devices I They are handled by dierent subsystems and dierent

658. lesystems I Block devices can be read and written to on a per-block basis, without erasing. I Hard disks, oppy disks, RAM disks I USB keys, Compact Flash, SD card: these are based on ash storage, but have an integrated controller that emulates a block device, managing and erasing ash sectors in a transparent way. I Flash devices can be read, but writing requires erasing, and often occurs on a larger size than the block size. I NOR ash, NAND ash Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 243/526

659. Block device list I The list of all block devices available in the system can be found in /proc/partitions $ cat /proc/partitions major minor #blocks name 179 0 3866624 mmcblk0 179 1 73712 mmcblk0p1 179 2 3792896 mmcblk0p2 8 0 976762584 sda 8 1 1060258 sda1 8 2 975699742 sda2 I And also in /sys/block/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 244/526

660. Traditional block

661. lesystems Traditional

662. lesystems I Can be left in a non-coherent state after a system crash or sudden powero, which requires a full

663. lesystem check after reboot. I ext2: traditional Linux

664. lesystem (repair it with fsck.ext2) I vfat: traditional Windows

665. lesystem (repair it with fsck.vfat on GNU/Linux or Scandisk on Windows) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 245/526

666. Journaled

667. lesystems I Designed to stay in a correct state even after system crashes or a sudden powero I All writes are

668. rst described in the journal before being committed to

670. Filesystem recovery after crashes I Thanks to the journal, the

671. lesystem is never left in a corrupted state I Recently saved data could still be lost Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 247/526

672. Journaled block

673. lesystems Journaled

674. lesystems I ext3: ext2 with journal extension ext4: the new generation with many improvements. Ready for production. They are the default

675. lesystems for all Linux systems in the world. I The Linux kernel supports many other

676. lesystems: reiserFS, JFS, XFS, etc. Each of them have their own characteristics, but are more oriented towards server or scienti

677. c workloads I Btrfs (Butter FS) The next generation. Great performance. In mainline but still experimental. We recommend ext2 for very small partitions ( 5 MB), because other

678. lesystems need too much space for metadata (ext3 and ext4 need about 1 MB for a 4 MB partition). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 248/526

679. Creating ext2/ext3/ext4 volumes I To create an empty ext2/ext3/ext4

680. lesystem on a block device or inside an already-existing image

681. le I mkfs.ext2 /dev/hda3 I mkfs.ext3 /dev/sda2 I mkfs.ext4 /dev/sda3 I mkfs.ext2 disk.img I To create a

682. lesystem image from a directory containing all your

683. les and directories I Use the genext2fs tool, from the package of the same name I genext2fs -d rootfs/ rootfs.img I Your image is then ready to be transferred to your block device Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 249/526

684. Mounting

685. lesystem images I Once a

686. lesystem image has been created, one can access and modi

687. es its contents from the development workstation, using the loop mechanism I Example: genext2fs -d rootfs/ rootfs.img mkdir /tmp/tst mount -t ext2 -o loop rootfs.img /tmp/tst I In the /tmp/tst directory, one can access and modify the contents of the rootfs.img

688. le. I This is possible thanks to loop, which is a kernel driver that emulates a block device with the contents of a

689. le. I Do not forget to run umount before using the

690. lesystem image! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 250/526

691. F2FS http://en.wikipedia.org/wiki/F2FS I Filesystem optimized for block devices based on NAND ash I Available in the mainline Linux kernel I Benchmarks: best performer on ash devices most of the time: See http://lwn.net/Articles/520003/ I Technical details: http://lwn.net/Articles/518988/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 251/526

692. Squashfs Squashfs: http://squashfs.sourceforge.net I Read-only, compressed

693. lesystem for block devices. Fine for parts of a

694. lesystem which can be read-only (kernel, binaries...) I Great compression rate and read access performance I Used in most live CDs and live USB distributions I Supports LZO compression for better performance on embedded systems with slow CPUs (at the expense of a slightly degraded compression rate) I Now supports XZ algorithm, for a much better compression rate, at the expense of higher CPU usage and time. Benchmarks: (roughly 3 times smaller than ext3, and 2-4 times faster) http://elinux.org/Squash_Fs_Comparisons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 252/526

695. Squashfs - How to use I Need to install the squashfs-tools package I Creation of the image I On your workstation, create your

696. lesystem image: mksquashfs rootfs/ rootfs.sqfs I Caution: if the image already exists remove it

697. rst, or use the -noappend option. I Installation of the image I Let's assume your partition on the target is in /dev/sdc1 I Copy the

698. lesystem image on the device dd if=rootfs.sqfs of=/dev/sdc1 Be careful when using dd to not overwrite the incorrect partition! I Mount your

699. lesystem: mount -t squashfs /dev/sdc1 /mnt/root Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 253/526

700. tmpfs Not a block

701. lesystem of course! Perfect to store temporary data in RAM: system log

702. les, connection data, temporary

703. les... I tmpfs con

704. guration: File systems - Pseudo filesystems Lives in the Linux

705. le cache. Doesn't waste RAM: unlike ramdisks, no need to copy

706. les to the

707. le cache, grows and shrinks to accommodate stored

708. les. Saves RAM: can swap out pages to disk when needed. I How to use: choose a name to distinguish the various tmpfs instances you could have. Examples: mount -t tmpfs varrun /var/run mount -t tmpfs udev /dev See Documentation/filesystems/tmpfs.txt in kernel sources. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 254/526

709. Mixing read-only and read-write

710. lesystems Good idea to split your block storage into: I A compressed read-only partition (Squashfs) Typically used for the root

711. lesystem (binaries, kernel...). Compression saves space. Read-only access protects your system from mistakes and data corruption. I A read-write partition with a journaled

712. lesystem (like ext3) Used to store user or con

713. guration data. Guarantees

714. lesystem integrity after power o or crashes. I Ram storage for temporary

715. les (tmpfs) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 255/526

716. Practical lab - Block

717. lesystems I Creating partitions on your block storage I Booting your system with a mix of

718. lesystems: SquashFS for the root

719. lesystem (including applications), ext3 for con

720. guration and user data, and tmpfs for temporary system

722. Flash

723. lesystems Flash

724. lesystems Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 257/526

725. The MTD subsystem MTD stands for Memory Technology Devices Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 258/526

726. MTD devices I MTD devices are visible in /proc/mtd I The mtdchar driver creates a character device for each MTD device of the system I Usually named /dev/mtdX or /dev/mtdXro, major 90. Even minors for read-write access (/dev/mtdX), odd minors for read-only access (/dev/mtdXro) I Provide ioctl() to erase and manage the ash I Used by the mtd-utils utilities I The mtdblock driver creates a block device for each MTD device of the system I Usually named /dev/mtdblockX, major 31. Minor is the number of the MTD device I Allows read/write block-level access. But bad blocks are not handled, and no wear leveling is done for writes. I Primary use: mounting

727. lesystems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 259/526

728. MTD partitioning I MTD devices are usually partitioned I It allows to use dierent areas of the ash for dierent purposes: read-only

729. lesystem, read-write

730. lesystem, backup areas, bootloader area, kernel area, etc. I Unlike block devices, which contains their own partition table, the partitioning of MTD devices is described externally I Speci

731. ed in the board Device Tree I Hard-coded into the kernel code (if no Device Tree) I Speci

732. ed through the kernel command line I Each partition becomes a separate MTD device I Dierent from block device labeling (hda3, sda2) I /dev/mtd1 is either the second partition of the

733. rst ash device, or the

734. rst partition of the second ash device Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 260/526

735. De

736. nition of MTD partitions (1) The Device Tree is the standard place to device MTD partitions for boards with Device Tree support. Example from arch/arm/boot/dts/omap3-igep0020.dts: nand@0,0 { linux,mtd-name= micron,mt29c4g96maz; [...] partition@0 { label = SPL; reg = 0 0x100000; }; partition@0x80000 { label = U-Boot; reg = 0x100000 0x180000; }; [...] partition@0x780000 { label = Filesystem; reg = 0x680000 0x1f980000; }; Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 261/526

737. De

738. nition of MTD partitions (2) For boards or platforms that do not use the Device Tree, MTD partitions can be de

739. ned in the kernel. Legacy example from arch/arm/mach-omap2/board-igep0020.c (removed in 3.13): static struct mtd_partition igep2_flash_partitions[] = { { .name = X-Loader, .offset = 0, .size = 2 * (64*(2*2048)) }, { .name = U-Boot, .offset = MTDPART_OFS_APPEND, .size = 6 * (64*(2*2048)), }, [...] { .name = File System, .offset = MTDPART_OFS_APPEND, .size = MTDPART_SIZ_FULL, }, }; Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 262/526

740. Modifying MTD partitions (1) I MTD partitions can fortunately be de

741. ned through the kernel command line. I First need to

742. nd the name of the MTD device. Look at the kernel log at boot time. In the below example, the MTD device name is omap2-nand.0: NAND device: Manufacturer ID: 0x2c, Chip ID: 0xbc (Micron NAND 512MiB 1,8V 16-bit) Creating 5 MTD partitions on omap2-nand.0: 0x000000000000-0x000000080000 : X-Loader 0x000000080000-0x000000200000 : U-Boot 0x000000200000-0x000000280000 : Environment 0x000000280000-0x000000580000 : Kernel 0x000000580000-0x000020000000 : File System Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 263/526

743. Modifying MTD partitions (2) I You can now use the mtdparts kernel boot parameter I Example: mtdparts=omap2-nand.0:512k(X-Loader)ro,1536k(U-Boot) ro,512k(Environment),4m(Kernel),16m(RootFS) ,-(Data) I We've just de

744. ned 6 partitions in the omap2-nand.0 device: I 1st stage bootloader (512 KiB, read-only) I U-Boot (1536 KiB, read-only) I U-Boot environment (512 KiB) I Kernel (4 MiB) I Root filesystem (16 MiB) I Data filesystem (Remaining space) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 264/526

745. Modifying MTD partitions (3) I Partition sizes must be multiple of the erase block size. You can use sizes in hexadecimal too. Remember the below sizes: 0x20000 = 128k, 0x100000 = 1m, 0x1000000 = 16m I ro lists the partition as read only I - is used to use all the remaining space. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 265/526

746. mtd-utils I A set of utilities to manipulate MTD devices I mtdinfo to get detailed information about an MTD device I flash_eraseall to completely erase a given MTD device I flashcp to write to NOR ash I nandwrite to write to NAND ash I UBI utilities I Flash

747. lesystem image creation tools: mkfs.jffs2, mkfs.ubifs I Usually available as the mtd-utils package in your distribution I Most commands now also available in BusyBox I See http://www.linux-mtd.infradead.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 266/526

748. js2 I Today's standard

749. lesystem for MTD ash I Nice features: on the y compression (saves storage space and reduces I/O), power down reliable, wear-leveling and ECC. I Drawbacks: doesn't scale well I Mount time depending on

750. lesystem size: the kernel has to scan the whole

751. lesystem at mount time, to read which block belongs to each

752. le. I Need to use the CONFIG_JFFS2_SUMMARY kernel option to store such information in ash. This dramatically reduces mount time (from 16 s to 0.8 s for a 128 MB partition). I http://www.linux-mtd. infradead.org/doc/jffs2.html Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 267/526

753. js2 - How to use On the Linux target I Need either the mtd-utils package from the MTD project, or their embedded variants from Busybox I Erase and format a partition with js2: flash_eraseall -j /dev/mtd2 I Mount the partition: mount -t jffs2 /dev/mtdblock2 /mnt/flash I Fill the contents by writing (copying through the network or from external storage) I Other possibility: use a js2 image (see next page to make it): flash_eraseall /dev/mtd2 nandwrite -p /dev/mtd2 rootfs.jffs2 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 268/526

754. How to create a js2 image I mkfs.jffs2 command available in the mtd-utils package. Caution: unlike some mkfs commands, it doesn't create a

755. lesystem, but a

756. lesystem image. I First,

757. nd the erase block size (on the target running Linux): cat /proc/mtd For example: 00040000 (256 KiB) I Then create the image on your workstation: mkfs.jffs2 --pad --no-cleanmarkers -- eraseblock=256 -d rootfs/ -o rootfs.jffs2 I The --pad option pads the js2 image contents until the end of the

758. nal erase block. I It is

759. ne if the js2 image is smaller than the MTD partition. The js2

760. le system will use the entire partition anyway. I The --no-cleanmarkers option is for NAND ash only. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 269/526

761. Mounting a js2 image on your host Useful to edit jffs2 images on your development system Mounting an MTD device as a loop device is a bit complex task. Here's an example for jffs2, for your reference: I First

762. nd the erase block size used to create the js2 image. Let's assume it is 256KiB (262144 bytes). I Create a block device from the image losetup /dev/loop0 root.jffs2 I Emulate an MTD device from a block device, using the block2mtd kernel module modprobe block2mtd block2mtd=/dev/loop0,262144 I Load the mtdblock driver if needed modprobe mtdblock I Finally, mount the

763. lesystem (create /mnt/jffs2 if needed) mount -t jffs2 /dev/mtdblock0 /mnt/jffs2 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 270/526

764. Initializing js2 partitions from U-boot You may not want to have mtd-utils on your target! I Create a JFFS2 image on your workstation I In the U-Boot prompt: I Download the js2 image to RAM with tftp Or copy this image to RAM from external storage (U-boot understands FAT

765. lesystems and supports USB storage) I Flash it inside an MTD partition (exact instructions depending on ash type, NOR or NAND, reuse the instructions used to ash your kernel). Make sure to write only the size of the image, not more! I Limitation: need to split the js2 image in several chunks if bigger than the RAM size. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 271/526

766. Booting from a js2 root partition I To boot on a js2 root

767. lesystem, add root=/dev/mtdblockx and rootfstype=jffs2 to the Linux command line arguments. I The Linux kernel cannot autodetect the type of a root

768. lesystem in MTD ash. That's why the rootfstype kernel parameter is needed. I For root partitions on a block device, using rootfstype (for example: rootfstype=ext3) can reduce boot time a little bit. This way, the kernel doesn't have to try all the block

769. lesystems it supports. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 272/526

770. yas2 I Mainly supports NAND ash I No compression I Wear leveling, ECC, power failure resistant I Fast boot time I Code available separately through git (Dual GPL / Proprietary license for non Linux operating systems) I http://www.yaffs.net/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 273/526

771. yas2 - How to use I Erase a partition: flash_eraseall /dev/mtd2 I The

772. lesystem is automatically formatted at the

773. rst mount: mount -t yaffs2 /dev/mtdblock2 /mnt/flash I Images can be created with the mkyaffs tool, from yaffs-utils http://code.google.com/p/yaffs2utils/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 274/526

774. UBI (1) Unsorted Block Images I http://www.linux-mtd.infradead.org/doc/ubi.html I Volume management system on top of MTD devices. I Allows to create multiple logical volumes and spread writes across all physical blocks. I Takes care of managing the erase blocks and wear leveling. Makes

775. lesystems easier to implement. I Wear leveling can operate on the whole storage, not only on individual partitions (strong advantage). I Volumes can be dynamically resized or, on the opposite, can be read-only (static). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 275/526

776. UBI (2) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 276/526

777. UBIFS http://www.linux-mtd. infradead.org/doc/ubifs.html I The next generation of the js2

778. lesystem, from the same linux-mtd developers. I Works on top of UBI volumes I Has a noticeable metadata overhead on very small partitions (4M, 8M) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 277/526

779. UBI layout example Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 278/526

780. UBI - Preparation I Have /dev/ mounted as a devtmpfs

781. lesystem I Erase your ash partition while preserving your erase counters ubiformat /dev/mtd1 See http://www.linux-mtd.infradead.org/faq/ubi.html if you face problems I Attach UBI to one (of several) of the MTD partitions: ubiattach /dev/ubi_ctrl -m 1 I This command creates the ubi0 device, which represent the full UBI space stored on MTD device 1 (new /dev/ubi0 character device) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 279/526

782. UBI - Volume management I Volume creation with ubimkvol I ubimkvol /dev/ubi0 -N test -s 116MiB I ubimkvol /dev/ubi0 -N test -m (max available size) I The volume is then identi

783. ed as ubi0:test for the mount/umount commands I Volume removal with ubirmvol I ubirmvol /dev/ubi0 -N test Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 280/526

784. UBIFS - How to use I When a UBI volume is created, creating an empty UBIFS

785. lesystem is just a matter of mounting it I mount -t ubifs ubi0:test /mnt/flash I Images of UBIFS

786. lesystems can be created using the mkfs.ubifs utility I mkfs.ubifs -m 4096 -e 252KiB -c 1000 - r rootfs/ ubifs.img I -m 4096, minimal I/O size (see /sys/class/mtd/mtdx/writesize). I -e 252KiB, logical erase block size (smaller than PEB size, look at dmesg) I -c 1000, maximum number of logical erase blocks. Details: http://linux-mtd.infradead.org/faq/ubifs.html#L_max_leb_cnt I Can be written to a UBI volume using ubiupdatevol: ubiupdatevol /dev/ubi0_0 /path/to/ubifs.img Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 281/526

787. Ubinize (1) After creating images of UBIFS

788. lesystems, images of a full UBI space, containing several volumes, can be created using ubinize: I Can be written to a raw MTD partition in U-boot. I Must be written using nand write.trimffs. I Caution: nand erase will also erase the Erase Counters First, create a con

789. guration

790. le describing the UBI volumes (ubi.ini): [RFS-volume] mode=ubi image=rootfs.ubifs vol_id=1 vol_size=30MiB vol_type=dynamic vol_name=rootfs vol_flags=autoresize vol_alignment=1 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 282/526

791. Ubinize (2) I ubinize -o ubi.img -p 256KiB -m 4096 ubi.ini I Creates ubi.img, with 256KiB physical erase blocks, 4096 minimum I/O size (-m). I See http://free-electrons.com/blog/creating-flashing- ubi-ubifs-images/ for details about creating UBI and UBIFS images. I See http://www.linux-mtd. infradead.org/doc/ubi.html#L_flasher_algo for what is required when ashing UBI images containing UBIFS volumes. I Build systems like Buildroot can run ubinize automatically! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 283/526

792. UBIFS - How to prepare a root fs I Create the UBIFS image for the root

793. lesystem I Create the UBI device image (with ubinize) I Flash it from the bootloader I Pass UBI layout information to the kernel: I rootfstype=ubifs ubi.mtd=1 root=ubi0:rootfs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 284/526

794. Flash

795. lesystem benchmarks http://elinux.org/Flash_Filesystem_Benchmarks I js2 I Worst performance I Requires CONFIG_SUMMARY to have acceptable boot time I yas2 I Good performance, but not in mainline Linux I ubifs I Best solution and performance for medium and big partitions I Too much metadata overhead small partitions (only case when yaffs2 and jffs2 are still useful) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 285/526

796. Issues with ash-based block storage I Flash storage made available only through a block interface. I Hence, no way to access a low level ash interface and use the Linux

797. lesystems doing wear leveling. I No details about the layer (Flash Translation Layer) they use. Details are kept as trade secrets, and may hide poor implementations. I Can use ashbench (https://github.com/bradfa/flashbench) to

798. nd out the erase block size and optimize

799. lesystem formating. I Not knowing about the wear leveling algorithm, it is highly recommended to limit the number of writes to these devices. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 286/526

800. Reducing the number of writes I Of course, do not use your ash storage as swap area (rare in embedded systems anyway) I Mount your

801. lesystems as read-only, or use read-only

802. lesystems (SquashFS), whenever possible. I Keep volatile

803. les in RAM (tmpfs) I Don't use the sync mount option (commits writes immediately). Use the fsync() system call for per-

804. le synchronization. I You may decide to do without journaled

805. lesystems. They cause more writes, but are also much more power down resistant (trade-o). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 287/526

806. Useful reading I Arnd Bergmann: Optimizing Linux with cheap ash drives In depth coverage of ash storage with a block interface. http://lwn.net/Articles/428584/ I Managing ash storage with Linux: http://free-electrons.com/blog/managing-flash-storage- with-linux/ I Documentation on the linux-mtd website: http://www.linux-mtd.infradead.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 288/526

807. Practical lab - Flash Filesystems I Creating partitions in your internal ash storage. I Use a read-only JFFS2 partition for the system I Use a read-write JFFS2 partition for data Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 289/526

808. Embedded Linux system development Embedded Linux system development Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 290/526

809. Contents I Using open-source components I Tools for the target device I Networking I System utilities I Language interpreters I Audio, video and multimedia I Graphical toolkits I Databases I Web browsers I System building I Commercial tool sets and distributions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 291/526

810. Embedded Linux system development Leveraging open-source components in an Embedded Linux system Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 292/526

811. Third party libraries and applications I One of the advantages of embedded Linux is the wide range of third-party libraries and applications that one can leverage in its product I They are freely available, freely distributable, and thanks to their open-source nature, they can be analyzed and modi

812. ed according to the needs of the project I However, eciently re-using these components is not always easy. One must: I Find these components I Choose the most appropriate ones I Cross-compile them I Integrate them in the embedded system and with the other applications Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 293/526

813. Find existing components I Free Software Directory http://directory.fsf.org I Look at other embedded Linux products, and see what their components are I Look at the list of software packaged by embedded Linux build systems I These are typically chosen for their suitability to embedded systems I Ask the community or Google I This presentation will also feature a list of components for common needs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 294/526

814. Choosing components I Not all free software components are necessarily good to re-use. One must pay attention to: I Vitality of the developer and user communities. This vitality ensures long-term maintenance of the component, and relatively good support. It can be measured by looking at the mailing-list trac and the version control system activity. I Quality of the component. Typically, if a component is already available through embedded build systems, and has a dynamic user community, it probably means that the quality is relatively good. I License. The license of the component must match your licensing constraints. For example, GPL libraries cannot be used in proprietary applications. I Technical requirements. Of course, the component must match your technical requirements. But don't forget that you can improve the existing components if a feature is missing! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 295/526

815. Licenses (1) I All software that are under a free software license give four freedoms to all users I Freedom to use I Freedom to study I Freedom to copy I Freedom to modify and distribute modi

816. ed copies I See http://www.gnu.org/philosophy/free-sw.html for a de

817. nition of Free Software I Open Source software, as per the de

818. nition of the Open Source Initiative, are technically similar to Free Software in terms of freedoms I See http://www.opensource.org/docs/osd for the de

819. nition of Open Source Software Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 296/526

820. Licenses (2) I Free Software licenses fall in two main categories I The copyleft licenses I The non-copyleft licenses I The concept of copyleft is to ask for reciprocity in the freedoms given to a user. I The result is that when you receive a software under a copyleft free software license and distribute modi

821. ed versions of it, you must do so under the same license I Same freedoms to the new users I It's an incentive to contribute back your changes instead of keeping them secret I Non-copyleft licenses have no such requirements, and modi

822. ed versions can be kept proprietary, but they still require attribution Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 297/526

823. GPL I GNU General Public License I Covers around 55% of the free software projects I Including the Linux kernel, Busybox and many applications I Is a copyleft license I Requires derivative works to be released under the same license I Programs linked with a library released under the GPL must also be released under the GPL I Some programs covered by version 2 (Linux kernel, Busybox and others) I More and more programs covered by version 3, released in 2007 I Major change for the embedded market: the requirement that the user must be able to run the modi

824. ed versions on the device, if the device is a consumer device Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 298/526

825. GPL: redistribution I No obligation when the software is not distributed I You can keep your modi

826. cations secret until the product delivery I It is then authorized to distribute binary versions, if one of the following conditions is met: I Convey the binary with a copy of the source on a physical medium I Convey the binary with a written oer valid for 3 years that indicates how to fetch the source code I Convey the binary with the network address of a location where the source code can be found I See section 6. of the GPL license I In all cases, the attribution and the license must be preserved I See section 4. and 5. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 299/526

827. LGPL I GNU Lesser General Public License I Covers around 10% of the free software projects I A copyleft license I Modi

828. ed versions must be released under the same license I But, programs linked against a library under the LGPL do not need to be released under the LGPL and can be kept proprietary. I However, the user must keep the ability to update the library independently from the program. Dynamic linking is the easiest solution. Statically linked executables are only possible if the developer provides a way to relink with an update (with source code or linkable object

829. les). I Used instead of the GPL for most of the libraries, including the C libraries I Some exceptions: MySQL, or Qt = 4.4 I Also available in two versions, v2 and v3 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 300/526

830. Licensing: examples I You make modi

831. cations to the Linux kernel (to add drivers or adapt to your board), to Busybox, U-Boot or other GPL software I You must release the modi

832. ed versions under the same license, and be ready to distribute the source code to your customers I You make modi

833. cations to the C library or any other LGPL library I You must release the modi

834. ed versions under the same license I You create an application that relies on LGPL libraries I You can keep your application proprietary, but you must link dynamically with the LGPL libraries I You make modi

835. cations to a non-copyleft licensed software I You can keep your modi

836. cations proprietary, but you must still credit the authors Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 301/526

837. Non-copyleft licenses I A large family of non-copyleft licenses that are relatively similar in their requirements I A few examples I Apache license (around 4%) I BSD license (around 6%) I MIT license (around 4%) I X11 license I Artistic license (around 9 %) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 302/526

838. BSD license Copyright (c) year, copyright holder All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name of the organization nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. [...] Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 303/526

839. Is this free software? I Most of the free software projects are covered by 10 well-known licenses, so it is fairly easy for the majority of project to get a good understanding of the license I Otherwise, read the license text I Check Free Software Foundation's opinion http://www.fsf.org/licensing/licenses/ I Check Open Source Initiative's opinion http://www.opensource.org/licenses Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 304/526

840. Respect free software licenses I Free Software is not public domain software, the distributors have obligations due to the licenses I Before using a free software component, make sure the license matches your project constraints I Make sure to keep a complete list of the free software packages you use, the original version you used and to keep your modi

841. cations and adaptations well-separated from the original version I Conform to the license requirements before shipping the product to the customers I Free Software licenses have been enforced successfully in courts. Organizations which can help: I GPL-violations.org, http://www.gpl-violations.org I Software Freedom Law Center, http://www.softwarefreedom.org/ I Software Freedom Conservancy, http://sfconservancy.org/ I Ask your legal department! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 305/526

842. Keeping changes separate (1) I When integrating existing open-source components in your project, it is sometimes needed to make modi

843. cations to them I Better integration, reduced footprint, bug

844. xes, new features, etc. I Instead of mixing these changes, it is much better to keep them separate from the original component version I If the component needs to be upgraded, easier to know what modi

845. cations were made to the component I If support from the community is requested, important to know how dierent the component we're using is from the upstream version I Makes contributing the changes back to the community possible I It is even better to keep the various changes made on a given component separate I Easier to review and to update to newer versions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 306/526

846. Keeping changes separate (2) I The simplest solution is to use Quilt I Quilt is a tool that allows to maintain a stack of patches over source code I Makes it easy to add, remove modi

847. cations from a patch, to add and remove patches from stack and to update them I The stack of patches can be integrated into your version control system I https://savannah.nongnu.org/projects/quilt/ I Another solution is to use a version control system I Import the original component version into your version control system I Maintain your changes in a separate branch Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 307/526

848. Embedded Linux system development Tools for the target device: Networking Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 308/526

849. ssh server and client: Dropbear http://matt.ucc.asn.au/dropbear/dropbear.html I Very small memory footprint ssh server for embedded systems I Satis

850. es most needs. Both client and server! I Size: 110 KB, statically compiled with uClibc on i386. (OpenSSH client and server: approx 1200 KB, dynamically compiled with glibc on i386) I Useful to: I Get a remote console on the target device I Copy

851. les to and from the target device (scp or rsync -e ssh). I An alternative to OpenSSH, used on desktop and server systems. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 309/526

852. Bene

853. ts of a web server interface Many network enabled devices can just have a network interface I Examples: modems / routers, IP cameras, printers... I No need to develop drivers and applications for computers connected to the device. No need to support multiple operating systems! I Just need to develop static or dynamic HTML pages (possibly with powerful client-side JavaScript). Easy way of providing access to device information and parameters. I Reduced hardware costs (no LCD, very little storage space needed) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 310/526

854. Web servers I BusyBox http server: http://busybox.net I Tiny: only adds 9 K to BusyBox (dynamically linked with glibc on i386, with all features enabled.) I Sucient features for many devices with a web interface, including CGI, http authentication and script support (like PHP, with a separate interpreter). I License: GPL I lighttpd: http://lighttpd.net Low footprint server good at managing high loads. May be useful in embedded systems too I Other possibilities: Boa, thttpd, nginx, etc Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 311/526

855. Network utilities (1) I avahi is an implementation of Multicast DNS Service Discovery, that allows programs to publish and discover services on a local network I bind, a DNS server I iptables, the user space tools associated to the Linux

856. rewall, Net

857. lter I iw and wireless tools, the user space tools associated to Wireless devices I netsnmp, implementation of the SNMP protocol I openntpd, implementation of the Network Time Protocol, for clock synchronization I openssl, a toolkit for SSL and TLS connections Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 312/526

858. Network utilities (2) I pppd, implementation of the Point to Point Protocol, used for dial-up connections I samba, implements the SMB and CIFS protocols, used by Windows to share

859. les and printers I coherence, a UPnP/DLNA implementation I vsftpd, proftpd, FTP servers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 313/526

860. Embedded Linux system development Tools for the target device: System utilities Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 314/526

861. System utilities I dbus, an inter-application object-oriented communication bus I gpsd, a daemon to interpret and share GPS data I libraw1394, raw access to Firewire devices I libusb, a user space library for accessing USB devices without writing an in-kernel driver I Utilities for kernel subsystems: i2c-tools for I2C, input-tools for input, mtd-utils for MTD devices, usbutils for USB devices Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 315/526

862. Embedded Linux system development Tools for the target device: Language interpreters Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 316/526

863. Language interpreters I Interpreters for the most common scripting languages are available. Useful for I Application development I Web services development I Scripting I Languages supported I Lua I Python I Perl I Ruby I TCL I PHP Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 317/526

864. Embedded Linux system development Tools for the target device: Audio, video and multimedia Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 318/526

865. Audio, video and multimedia I GStreamer, a multimedia framework I Allows to decode/encode a wide variety of codecs. I Supports hardware encoders and decoders through plugins, proprietary/speci

866. c plugins are often provided by SoC vendors. I alsa-lib, the user space tools associated to the ALSA sound kernel subsystem I Directly using encoding and decoding libraries, if you decide not to use GStreamer: libavcodec, libogg, libtheora, libvpx, ac, libvorbis, libmad, libsnd

867. le, speex, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 319/526

868. Embedded Linux system development Tools for the target device: Graphical toolkits Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 320/526

869. Embedded Linux system development Graphical toolkits: Low-level solutions and layers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 321/526

870. DirectFB (1) I Low-level graphical library I Lines, rectangles, triangles drawing and

871. lling I Blitting, ipping I Text drawing I Windows and transparency I Image loading and video display I But also handles input event handling: mice, keyboards, joysticks, touchscreens, etc. I Provides accelerated graphic operations on a few hardware platforms I Single-application by default, but multiple applications can share the framebuer thanks to fusion I License: LGPL 2.1 I http://www.directfb.org Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 322/526

872. DirectFB: architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 323/526

873. DirectFB: usage (1) I Multimedia applications I For example the Disko framework, for set-top box related applications I Simple graphical applications I Industrial control I Device control with limited number of widgets I Visualization applications I As a lower layer for higher-level graphical libraries Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 324/526

874. DirectFB: architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 325/526

875. X.org - KDrive I Stand-alone simpli

876. ed version of the X server, for embedded systems I Formerly know as Tiny-X I Kdrive is integrated in the ocial X.org server I Works on top of the Linux frame buer, thanks to the Xfbdev variant of the server I Real X server I Fully supports the X11 protocol: drawing, input event handling, etc. I Allows to use any existing X11 application or library I Actively developed and maintained. I X11 license I http://www.x.org Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 326/526

877. Kdrive: architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 327/526

878. Kdrive: usage I Can be directly programmed using Xlib / XCB I Low-level graphic library I Probably doesn't make sense since DirectFB is a more lightweight solution for an API of roughly the same level (no widgets) I Or, usually used with a toolkit on top of it I Gtk I Qt I Enlightment Foundation Libraries I Others: Fltk, WxEmbedded, etc Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 328/526

879. Wayland I Intended to be a simpler replacement for X I Wayland is a protocol for a compositor to talk to its clients as well as a C library implementation of that protocol. I Weston: a minimal and fast reference implementation of a Wayland compositor, and is suitable for many embedded and mobile use cases. I Still experimental. Porting Gtk and Qt to Wayland is not complete yet, for example. I http://wayland.freedesktop.org/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 329/526

880. Wayland: architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 330/526

881. Embedded Linux system development Graphical toolkits: High-level solutions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 331/526

882. Gtk I The famous toolkit, providing widget-based high-level APIs to develop graphical applications I Standard API in C, but bindings exist for various languages: C++, Python, etc. I Works on top of X.org. I No windowing system, a lightweight window manager needed to run several applications. Possible solution: Matchbox. I License: LGPL I http://www.gtk.org Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 332/526

883. Gtk stack components I Glib, core infrastructure I Object-oriented infrastructure GObject I Event loop, threads, asynchronous queues, plug-ins, memory allocation, I/O channels, string utilities, timers, date and time, internationalization, simple XML parser, regular expressions I Data types: memory slices and chunks, linked lists, arrays, trees, hash tables, etc. I Pango, internationalization of text handling I ATK, accessibility toolkit I Cairo, vector graphics library I Gtk+, the widget library itself I The Gtk stack is a complete framework to develop applications Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 333/526

884. Gtk examples (1) Openmoko phone interface Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 334/526

885. Gtk examples (2) Maemo tablet / phone interface GTK is losing traction, however: Mer, the descendent of Maemo, is now implemented in EFL (see next slides). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 335/526

886. Qt (1) I The other famous toolkit, providing widget-based high-level APIs to develop graphical applications I Implemented in C++ I the C++ library is required on the target system I standard API in C++, but with bindings for other languages I Works either on top of I Framebuer I X11 I DirectFB back-end integrated in version 4.4, which allows to take advantage of the acceleration provided by DirectFB drivers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 336/526

887. Qt (2) I Qt is more than just a graphical toolkit, it also oers a complete development framework: data structures, threads, network, databases, XML, etc. I See our presentation Qt for non graphical applications presentation at ELCE 2011 (Thomas Petazzoni): http://j.mp/W4PK85 I Qt Embedded has an integrated windowing system, allowing several applications to share the same screen I Very well documented I Since version 4.5, available under the LGPL, allowing proprietary applications Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 337/526

888. Qt's usage Qt on the Dash Express navigation system Qt on the Net ix player by Roku Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 338/526

889. Other less frequent solutions I Enlightenment Foundation Libraries (EFL) I Very powerful. Supported by Samsung, Intel and Free.fr. I Work on top of X or Wayland. I http://www.enlightenment.org/p.php?p=about/efl Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 339/526

890. Embedded Linux system development Tools for the target device: Databases Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 340/526

891. Lightweight database - SQLite http://www.sqlite.org I SQLite is a small C library that implements a self-contained, embeddable, lightweight, zero-con

892. guration SQL database engine I The database engine of choice for embedded Linux systems I Can be used as a normal library I Can be directly embedded into a application, even a proprietary one since SQLite is released in the public domain Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 341/526

893. Embedded Linux system development Tools for the target device: Web browsers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 342/526

894. WebKit http://webkit.org/ I Web browser engine. Application framework that can be used to develop web browsers. I License: portions in LGPL and others in BSD. Proprietary applications allowed. I Used by many web browsers: Safari, iPhone et Android default browsers ... Google Chrome now uses a fork of its WebCore component). Used by e-mail clients too to render HTML: http://trac.webkit.org/wiki/ Applications%20using%20WebKit I Multiple graphical back-ends: Qt4, GTK, EFL... I You could use it to create your custom browser. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 343/526

895. Embedded Linux system development Example of components used in real devices Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 344/526

896. Industrial applications I In many industrial applications, the system is only responsible for monitoring and control a device I Such a system is usually relatively simple in terms of components I Kernel I BusyBox I C library I Applications relying directly on the C library, sometimes using the real-time capabilities of the Linux kernel I Sometimes a Web server for remote control, or another server implementing a custom protocol Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 345/526

897. Digital Photo Frame: requirements I Example taken from a conference of Matt Porter, Embedded Alley at ELC 2008 I Hardware: ARM SoC with DSP, audio, 800x600 LCD, MMC/SD, NAND, buttons, speakers I The photo frame must be able to I Display to the LCD I Detect SD card insertion, notify applications of the insertion so that applications can build a catalog of the pictures on the SD card I Modern 3D GUI with nice transitions I Navigation through buttons I Support audio playback (MP3, playlists, ID3 tag) I JPEG resizing and rotation Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 346/526

898. Digital Photo Frame: components (1) I Base system I Components present in virtually all embedded Linux systems I The U-Boot bootloader I Linux Kernel I Drivers for SD/MMC, framebuer, sound, input devices I Busybox I Build system, in this case was OpenEmbedded I Components: u-boot, Linux, busybox Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 347/526

899. Digital Photo Frame: components (2) I Event handling to detect SD card insertion I udev, that receives events from the kernel, creates device nodes, and sends events to hal I hal, which maintains a database of available devices and provides a dbus API I dbus to connect hal with the application. The application subscribes to hal event through dbus and gets noti

900. ed when they are triggered I Components: udev, hal, dbus Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 348/526

901. Digital Photo Frame: components (3) I JPEG display I libjpeg to decode the pictures I jpegtran to resize and rotate them I FIM (Fbi Improved) for dithering I MP3 support I libmad for playing I libid3 for ID3 tags reading I libm3u to support playlists I Used vendor-provided components to leverage the DSP to play MP3 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 349/526

902. Digital Photo Frame: components (4) I 3D interface I Vincent, an open-source implementation of OpenGL ES I Clutter, higher-level API to develop 3D applications I Application itself I Manages media events I Uses the JPEG libraries to decode and render pictures I Receives Linux input events from buttons and draws OpenGL-based UI developed with Clutter I Manage a user-de

903. ned con

904. guration I Play the music with the MP3-related libraries I Display photo slideshow Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 350/526

905. Embedded Linux system development System building Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 351/526

906. System building: goal and solutions I Goal I Integrate all the software components, both third-party and in-house, into a working root

907. lesystem I It involves the download, extraction, con

908. guration, compilation and installation of all components, and possibly

909. xing issues and adapting con

910. guration

911. les I Several solutions I Manually I System building tools I Distributions or ready-made

912. lesystems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 352/526

913. System building: manually I Manually building a target system involves downloading, con

914. guring, compiling and installing all the components of the system. I All the libraries and dependencies must be con

915. gured, compiled and installed in the right order. I Sometimes, the build system used by libraries or applications is not very cross-compile friendly, so some adaptations are necessary. I There is no infrastructure to reproduce the build from scratch, which might cause problems if one component needs to be changed, if somebody else takes over the project, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 353/526

916. System building: manually (2) I Manual system building is not recommended for production projects I However, using automated tools often requires the developer to dig into speci

917. c issues I Having a basic understanding of how a system can be built manually is therefore very useful to

918. x issues encountered with automated tools I We will

919. rst study manual system building, and during a practical lab, create a system using this method I Then, we will study the automated tools available, and use one of them during a lab Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 354/526

920. System foundations I A basic root

921. le system needs at least I A traditional directory hierarchy, with /bin, /etc, /lib, /root, /usr/bin, /usr/lib, /usr/share, /usr/sbin, /var, /sbin I A set of basic utilities, providing at least the init program, a shell and other traditional Unix command line tools. This is usually provided by Busybox I The C library and the related libraries (thread, math, etc.) installed in /lib I A few con

922. guration

923. les, such as /etc/inittab, and initialization scripts in /etc/init.d I On top of this foundation common to most embedded Linux system, we can add third-party or in-house components Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 355/526

924. Target and build spaces I The system foundation, Busybox and C library, are the core of the target root

925. lesystem I However, when building other components, one must distinguish two directories I The target space, which contains the target root

926. lesystem, everything that is needed for execution of the application I The build space, which will contain a lot more

927. les than the target space, since it is used to keep everything needed to compile libraries and applications. So we must keep the headers, documentation, and other con

928. guration

930. Build systems I Each open-source component comes with a mechanism to con

931. gure, compile and install it I A basic Makefile I Need to read the Makefile to understand how it works and how to tweak it for cross-compilation I A build system based on the Autotools I As this is the most common build system, we will study it in details I CMake, http://www.cmake.org/ I Newer and simpler than the autotools. Used by large projects such as KDE or Second Life I Scons, http://www.scons.org/ I Waf, http://code.google.com/p/waf/ I Other manual build systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 357/526

932. Autotools and friends I A family of tools, which associated together form a complete and extensible build system I autoconf is used to handle the con

933. guration of the software package I automake is used to generate the Make

934. les needed to build the software package I pkgcon

935. g is used to ease compilation against already installed shared libraries I libtool is used to handle the generation of shared libraries in a system-independent way I Most of these tools are old and relatively complicated to use, but they are used by a majority of free software packages today. One must have a basic understanding of what they do and how they work. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 358/526

936. automake / autoconf / autoheader Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 359/526

937. automake / autoconf I Files written by the developer I configure.in describes the con

938. guration options and the checks done at con

939. gure time I Makefile.am describes how the software should be built I The configure script and the Makefile.in

940. les are generated by autoconf and automake respectively. I They should never be modi

941. ed directly I They are usually shipped pre-generated in the software package, because there are several versions of autoconf and automake, and they are not completely compatible I The Makefile

942. les are generated at con

943. gure time, before compiling I They are never shipped in the software package. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 360/526

944. Con

945. guring and compiling: native case I The traditional steps to con

946. gure and compile an autotools based package are I Con

947. guration of the package ./configure I Compilation of the package make I Installation of the package make install I Additional arguments can be passed to the ./configure script to adjust the component con

948. guration. I Only the make install needs to be done as root if the installation should take place system-wide Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 361/526

949. Con

950. guring and compiling: cross case (1) I For cross-compilation, things are a little bit more complicated. I At least some of the environment variables AR, AS, LD, NM, CC, GCC, CPP, CXX, STRIP, OBJCOPY must be de

951. ned to point to the proper cross-compilation tools. The host tuple is also by default used as pre

952. x. I configure script arguments: I --host: mandatory but a bit confusing. Corresponds to the target platform the code will run on. Example: --host=arm-linux I --build: build system. Automatically detected. I --target is only for tools generating code. I It is recommended to pass the --prefix argument. It de

953. nes from which location the software will run in the target environment. Usually, /usr is

954. ne. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 362/526

955. Con

956. guring and compiling: cross case (2) I If one simply runs make install, the software will be installed in the directory passed as --prefix. For cross-compiling, one must pass the DESTDIR argument to specify where the software must be installed. I Making the distinction between the pre

957. x (as passed with --prefix at con

958. gure time) and the destination directory (as passed with DESTDIR at installation time) is very important. I Example: export PATH=/usr/local/arm-linux/bin:$PATH export CC=arm-linux-gcc export STRIP=arm-linux-strip ./configure --host=arm-linux --prefix=/usr make make DESTDIR=$HOME/work/rootfs install Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 363/526

959. Installation (1) I The autotools based software packages provide both a install and install-strip make targets, used to install the software, either stripped or unstripped. I For applications, the software is usually installed in prefix/bin, with con

960. guration

961. les in prefix/etc and data in prefix/share/application/ I The case of libraries is a little more complicated: I In prefix/lib, the library itself (a .so.version), a few symbolic links, and the libtool description

962. le (a .la

963. le) I The pkgcon

964. g description

965. le in prefix/lib/pkgconfig I Include

966. les in prefix/include/ I Sometimes a libname-config program in prefix/bin I Documentation in prefix/share/man or prefix/share/doc/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 364/526

967. Installation (2) Contents of usr/lib after installation of libpng and zlib I libpng libtool description

968. les ./lib/libpng12.la ./lib/libpng.la - libpng12.la I libpng static version ./lib/libpng12.a ./lib/libpng.a - libpng12.a I libpng dynamic version ./lib/libpng.so.3.32.0 ./lib/libpng12.so.0.32.0 ./lib/libpng12.so.0 - libpng12.so.0.32.0 ./lib/libpng12.so - libpng12.so.0.32.0 ./lib/libpng.so - libpng12.so ./lib/libpng.so.3 - libpng.so.3.32.0 I libpng pkg-con

969. g description

970. les ./lib/pkgconfig/libpng12.pc ./lib/pkgconfig/libpng.pc - libpng12.pc I zlib dynamic version ./lib/libz.so.1.2.3 ./lib/libz.so - libz.so.1.2.3 ./lib/libz.so.1 - libz.so.1.2.3 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 365/526

971. Installation in the build and target spaces I From all these

972. les, everything except documentation is necessary to build an application that relies on libpng. I These

973. les will go into the build space I However, only the library .so binaries in prefix/lib and some symbolic links are needed to execute the application on the target. I Only these

974. les will go in the target space I The build space must be kept in order to build other applications or recompile existing applications. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 366/526

975. pkg-con

976. g I pkg-config is a tool that allows to query a small database to get information on how to compile programs that depend on libraries I The database is made of .pc

977. les, installed by default in prefix/lib/pkgconfig/. I pkg-config is used by the configure script to get the library con

978. gurations I It can also be used manually to compile an application: arm-linux-gcc -o test test.c $(pkg-config -- libs --cflags thelib) I By default, pkg-config looks in /usr/lib/pkgconfig for the *.pc

979. les, and assumes that the paths in these

980. les are correct. I PKG_CONFIG_PATH allows to set another location for the *.pc

981. les and PKG_CONFIG_SYSROOT_DIR to prepend a pre

982. x to the paths mentioned in the .pc

984. Let's

985. nd the libraries I When compiling an application or a library that relies on other libraries, the build process by default looks in /usr/lib for libraries and /usr/include for headers. I The

986. rst thing to do is to set the CFLAGS and LDFLAGS environment variables: export CFLAGS=-I/my/build/space/usr/include/ export LDFLAGS=-L/my/build/space/usr/lib I The libtool

987. les (.la

988. les) must be modi

989. ed because they include the absolute paths of the libraries: - libdir='/usr/lib' + libdir='/my/build/space/usr/lib' I The PKG_CONFIG_PATH environment variable must be set to the location of the .pc

990. les and the PKG_CONFIG_SYSROOT_DIR variable must be set to the build space directory. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 368/526

991. Practical lab - Manual cross-compiling I Manually cross-compiling applications and libraries I Learning about common techniques and issues. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 369/526

992. System building tools: principle I Dierent tools are available to automate the process of building a target system, including the kernel, and sometimes the toolchain. I They automatically download, con

993. gure, compile and install all the components in the right order, sometimes after applying patches to

994. x cross-compiling issues. I They already contain a large number of packages, that should

995. t your main requirements, and are easily extensible. I The build becomes reproducible, which allows to easily change the con

996. guration of some components, upgrade them,

997. x bugs, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 370/526

998. Available system building tools Large choice of tools I Buildroot, developed by the community http://www.buildroot.net I PTXdist, developed by Pengutronix http://pengutronix.de/software/ptxdist/ I OpenWRT, originally a fork of Buildroot for wireless routers, now a more generic project http://www.openwrt.org I LTIB. Good support for Freescale boards, but small community http://ltib.org/ I OpenEmbedded, more exible but also far more complicated http://www.openembedded.org, its industrialized version Yocto and vendor-speci

999. c derivatives such as Arago I Vendor speci

1000. c tools (silicon vendor or embedded Linux vendor) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 371/526

1001. Buildroot (1) I Allows to build a toolchain, a root

1002. lesystem image with many applications and libraries, a bootloader and a kernel image I Or any combination of the previous items I Supports building uClibc, glibc, eglibc and musl toolchains, either built by Buildroot, or external I Over 1200+ applications or libraries integrated, from basic utilities to more elaborate software stacks: X.org, GStreamer, Qt, Gtk, WebKit, Python, PHP, etc. I Good for small to medium embedded systems, with a

1003. xed set of features I No support for generating packages (.deb or .ipk) I Needs complete rebuild for most con

1004. guration changes. I Active community, releases published every 3 months. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 372/526

1005. Buildroot (2) I Con

1006. guration takes place through a *config interface similar to the kernel make menuconfig I Allows to de

1007. ne I Architecture and speci

1008. c CPU I Toolchain con

1009. guration I Set of applications and libraries to integrate I Filesystem images to generate I Kernel and bootloader con

1010. guration I Build by just running make Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 373/526

1011. Buildroot: adding a new package (1) I A package allows to integrate a user application or library to Buildroot I Each package has its own directory (such as package/gqview). This directory contains: I A Config.in

1012. le (mandatory), describing the con

1013. guration options for the package. At least one is needed to enable the package. This

1014. le must be sourced from package/Config.in I A gqview.mk

1015. le (mandatory), describing how the package is built. I Patches (optional). Each

1016. le of the form gqview-*.patch will be applied as a patch. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 374/526

1017. Buildroot: adding a new package (2) I For a simple package with a single con

1018. guration option to enable/disable it, the Config.in

1019. le looks like: config BR2_PACKAGE_GQVIEW bool gqview depends on BR2_PACKAGE_LIBGTK2 help GQview is an image viewer for Unix operating systems http://prdownloads.sourceforge.net/gqview I It must be sourced from package/Config.in: source package/gqview/Config.in Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 375/526

1020. Buildroot: adding new package (3) I Create the gqview.mk

1021. le to describe the build steps GQVIEW_VERSION = 2.1.5 GQVIEW_SOURCE = gqview-$(GQVIEW_VERSION).tar.gz GQVIEW_SITE = http://prdownloads.sourceforge.net/gqview GQVIEW_DEPENDENCIES = host-pkgconf libgtk2 GQVIEW_CONF_ENV = LIBS=-lm $(eval $(autotools-package)) I The package directory and the pre

1022. x of all variables must be identical to the sux of the main con

1023. guration option BR2_PACKAGE_GQVIEW I The autotools-package infrastructure knows how to build autotools packages. A more generic generic-package infrastructure is available for packages not using the autotools as their build system. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 376/526

1024. OpenEmbedded / Yocto I The most versatile and powerful embedded Linux build system I A collection of recipes (.bb

1025. les) I A tool that processes the recipes: bitbake I Integrates 2000+ application and libraries, is highly con

1026. gurable, can generate binary packages to make the system customizable, supports multiple versions/variants of the same package, no need for full rebuild when the con

1027. guration is changed. I Con

1028. guration takes place by editing various con

1029. guration

1030. les I Good for larger embedded Linux systems, or people looking for more con

1031. gurability and extensibility I Drawbacks: very steep learning curve, very long

1032. rst build. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 377/526

1033. Distributions - Debian Debian GNU/Linux, http://www.debian.org I Provides the easiest environment for quickly building prototypes and developing applications. Countless runtime and development packages available. I But brobably too costly to maintain and unnecessarily big for production systems. I Available on ARM, MIPS and PowerPC architectures I Software is compiled natively by default. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 378/526

1034. Distributions - Others Fedora I http://fedoraproject.org/wiki/ Architectures/ARM I Supported on various recent ARM boards (such as Beaglebone Black). Pidora supports Raspberry Pi too. I Supports QEMU emulated ARM boards too (Versatile Express board) I Shipping the same version as for desktops! Ubuntu I Had some releases for ARM mobile multimedia devices, but stopped at version 12.04. Now focusing on ARM servers only. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 379/526

1035. Embedded distributions Distributions designed for speci

1036. c types of devices I Android: http://www.android.com/ Google's distribution for phones and tablet PCs. Except the Linux kernel, very dierent user space than other Linux distributions. Very successful, lots of applications available (many proprietary). I Angstrom: http://www.angstrom-distribution.org/ Targets PDAs and webpads (Siemens Simpad...) Binaries available for arm little endian. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 380/526

1037. Application frameworks Not real distributions you can download. Instead, they implement middleware running on top of the Linux kernel and allowing to develop applications. I Mer: http://merproject.org/ Fork from the Meego project. Targeting mobile devices. Supports x86, ARM and MIPS. See http://en.wikipedia.org/wiki/Mer_ (software_distribution) I Tizen: https://www.tizen.org/ Targeting smartphones, tablets, netbooks, smart TVs and In Vehicle Infotainment devices. Supported by big phone manufacturers and operators HTML5 base application framework. Likely to compete against Android! See http://en.wikipedia.org/wiki/Tizen Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 381/526

1038. System emulator: QEMU http://qemu.org Fast processor emulator I Useful to develop root

1039. lesystems and applications when the hardware is not available yet (binary compatible development boards are also possible). I Emulates the processor and various peripherals (System emulation): x86, ppc, arm, sparc, mips, m68k... I Many dierent ARM boards supported: qemu-system-arm -M ? I QEMU also allows to just run binaries for other architectures (User emulation). Used inside some building tools. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 382/526

1040. Practical lab - Buildroot I Rebuild the same system, this time with Buildroot. I See how easier it gets! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 383/526

1041. Embedded Linux system development Commercial embedded Linux solutions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 384/526

1042. Commercial embedded Linux solutions Caution: commercial doesn't mean proprietary! I Vendors play fair with the GPL and do make their source code available to their users, and most of the time, eventually to the community. I As long as they distribute the sources to their users, the GPL doesn't require vendors to share their sources with any third party. I Graphical toolkits developed by the vendors are usually proprietary, trying to make it easier to create and embedded Linux systems. I Major players: Wind River, Montavista, TimeSys Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 385/526

1043. Commercial solution strengths I Technical advantages I Well tested and supported kernel and tool versions I Often supporting patches not supported by the mainline kernel yet (example: real-time patches) I Complete development tool sets: kernels, toolchains, utilities, binaries for impressive lists of target platforms I Integrated utilities for automatic kernel image, initramfs and

1044. lesystem generation. I Graphical developments tools I Development tools available on multiple platforms: GNU / Linux, Solaris, Windows... I Support services I Useful if you don't have your own support resources I Long term support commitment, even for versions considered as obsolete by the community, but not by your users! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 386/526

1045. Commercial or community solutions? Commercial distributions and tool sets I Best if you don't have your own support resources and have a sucient budget I Help focusing on your primary job: making an embedded device. I You can even subcontract driver development to the vendor Community distributions and tools I Best if you are on a tight budget I Best if you are willing to build your own embedded Linux expertise, investigate issues by yourselves, and train your own support resources. In any case, your products are based on Free Software! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 387/526

1046. Embedded Linux application development Embedded Linux application development Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 388/526

1047. Contents I Application development I Developing applications on embedded Linux I Building your applications I Source management I Integrated development environments (IDEs) I Version control systems I Debugging and analysis tools I Debuggers I Memory checkers I System analysis I Development environments I Developing on Windows Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 389/526

1048. Embedded Linux application development Developing applications on embedded Linux Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 390/526

1049. Application development I An embedded Linux system is just a normal Linux system, with usually a smaller selection of components I In terms of application development, developing on embedded Linux is exactly the same as developing on a desktop Linux system I All existing skills can be re-used, without any particular adaptation I All existing libraries, either third-party or in-house, can be integrated into the embedded Linux system I Taking into account, of course, the limitation of the embedded systems in terms of performance, storage and memory Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 391/526

1050. Programming language I The default programming language for system-level application in Linux is usually C I The C library is already present on your system, nothing to add I C++ can be used for larger applications I The C++ library must be added to the system I Some libraries, including Qt, are developed in C++ so they need the C++ library on the system anyway I Scripting languages can also be useful for quick application development, web applications or scripts I But they require an interpreter on the embedded system and have usually higher memory consumption and slightly lower performance I Languages: Python, Perl, Lua, Ada, Fortran, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 392/526

1051. C library or higher-level libraries? I For many applications, the C library already provides a relatively large set of features I

1052. le and device I/O, networking, threads and synchronization, inter-process communication I Thoroughly described in the glibc manual, or in any Linux system programming book I However, the API carries a lot of history and is not necessarily easy to grasp for new comers I Therefore, using a higher level framework, such as Qt or the Gtk stack, might be a good idea I These frameworks are not only graphical libraries, their core is separate from the graphical part I But of course, these libraries have some memory and storage footprint, in the order of a few megabytes Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 393/526

1053. Building your applications I For simple applications that do not need to be really portable or provide compile-time con

1054. guration options, a simple Make

1055. le will be sucient I For more complicated applications, or if you want to be able to run your application on a desktop Linux PC and on the target device, using a build system is recommended I autotools is ancient, complicated but very widely used. I We recommend to invest in CMake instead: modern, simpler, smaller but growing user base. I The QT library is a special case, since it comes with its own build system for applications, called qmake. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 394/526

1056. Simple Make

1057. le (1) I Case of an application that only uses the C library, contains two source

1058. les and generates a single binary CROSS_COMPILE?=arm-linux- CC=$(CROSS_COMPILE)gcc OBJS=foo.o bar.o all: foobar foobar: $(OBJS) $(CC) -o $@ $^ clean: $(RM) -f foobar $(OBJS) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 395/526

1059. Simple Make

1060. le (2) I Case of an application that uses the Glib and the GPS libraries CROSS_COMPILE?=arm-linux- LIBS=libgps glib-2.0 OBJS=foo.o bar.o CC=$(CROSS_COMPILE)gcc CFLAGS=$(shell pkg-config --cflags $(LIBS)) LDFLAGS=$(shell pkg-config --libs $(LIBS)) all: foobar foobar: $(OBJS) $(CC) -o $@ $^ $(LDFLAGS) clean: $(RM) -f foobar $(OBJS) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 396/526

1061. Embedded Linux application development Integrated Development Environments (IDE) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 397/526

1062. KDevelop http://kdevelop.org I A full featured IDE! I License: GPL I Supports many languages: Ada, C, C++, Database, Java, Perl, PHP, Python, Ruby, Shell I Supports many kinds of projects: KDE, but also GTK, Gnome, kernel drivers, embedded (Opie)... I Many features: editor, syntax highlighting, code completion, compiler interface, debugger interface,

1063. le manager, class browser... Nice overview: http://en.wikipedia.org/wiki/Kdevelop Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 398/526

1064. KDevelop screenshot Ruby debugger Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 399/526

1065. Eclipse (1) http://www.eclipse.org/ I An extensible, plug-in based software development kit, typically used for creating IDEs. I Supported by the Eclipse foundation, a non-pro

1066. t consortium of major software industry vendors (IBM, Intel, Borland, Nokia, Wind River, Zend, Computer Associates...). I Free Software license (Eclipse Public License). Incompatible with the GPL. I Supported platforms: GNU/Linux, Unix, Windows Extremely popular: created a lot of attraction. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 400/526

1067. Eclipse (2) I Eclipse is actually a platform composed of many projects: http://www.eclipse.org/projects/ I Some projects are dedicated to integrating into Eclipse features useful for embedded developers (cross-compilation, remote development, remote debugging, etc.) I The platform is used by major embedded Linux software vendors for their (proprietary) system development kits: MontaVista DevRocket, TimeSys TimeStorm, Wind River Workbench, Sysgo ELinOS. I Used by free software build systems and development environments too, such as Yocto and Buildroot. Eclipse is a huge project. It would require an entire training session! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 401/526

1068. Other popular solutions I Many embedded Linux developers simply use Vim or Emacs. They can integrate with debuggers, source code browsers such as cscope, oer syntax highlighting and more. I Geany is an easy-to-use graphical code editor. I CodeBlocks is also quite popular, since it's also available on the Windows platform. All these editors are available in most Linux distributions, simply install them and try them out! Vim Emacs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 402/526

1069. Embedded Linux application development Version control systems Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 403/526

1070. Version control systems Real projects can't do without them I Allow multiple developers to contribute on the same project. Each developer can see the latest changes from the others, or choose to stick with older versions of some components. I Allow to keep track of changes, and revert them if needed. I Allow developers to have their own development branch (branching) I Supposed to help developers resolving con icts with dierent branches (merging) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 404/526

1071. Traditional version control systems Rely on a central repository. The most popular open-source ones: I CVS - Concurrent Versions System I Still quite popular in enterprise contexts. Almost no longer exists in the open-source community. I Should no longer be used for new projects I http: //en.wikipedia.org/wiki/Concurrent_Versions_System I Subversion I Created as a replacement of CVS, removing many of its limitations. I Commits on several

1072. les, proper renaming support, better performance, etc. I The user interface is very similar to CVS I http://en.wikipedia.org/wiki/Subversion_(software) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 405/526

1073. Distributed source control systems (1) No longer have a central repository I More adapted to the way the Free Software community develops software and organizes I Allows each developer to have a full local history of the project, to create local branches. Makes each developer's work easier. I People get working copies from other people's working copies, and exchange changes between themselves. Branching and merging is made easier. I Make it easier for new developers to join, making their own experiments without having to apply for repository access. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 406/526

1074. Distributed source control systems (2) I Git I Initially designed and developed by Linus Torvalds for Linux kernel development I Extremely popular in the community, and used by more and more projects (kernel, U-Boot, Barebox, uClibc, GNOME, X.org, etc.) I Outstanding performance, in particular in big projects I http://en.wikipedia.org/wiki/Git_(software) I Mercurial I Another system, created with the same goals as Git. I Used by some big projects too I http://en.wikipedia.org/wiki/Mercurial http://en.wikipedia.org/wiki/Version_control_systems# Distributed_revision_control Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 407/526

1075. Embedded Linux application development Debuggers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 408/526

1076. GDB The GNU Project Debugger http://www.gnu.org/software/gdb/ I The debugger on GNU/Linux, available for most embedded architectures. I Supported languages: C, C++, Pascal, Objective-C, Fortran, Ada... I Console interface (useful for remote debugging). I Graphical front-ends available. I Can be used to control the execution of a program, set breakpoints or change internal variables. You can also use it to see what a program was doing when it crashed (by loading its memory image, dumped into a core

1077. le). See also http://en.wikipedia.org/wiki/Gdb Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 409/526

1078. GDB crash course I A few useful GDB commands I break foobar puts a breakpoint at the entry of function foobar() I break foobar.c:42 puts a breakpoint in foobar.c, line 42 I print var or print task-files[0].fd prints the variable var, or a more complicated reference. GDB can also nicely display structures with all their members I continue continue the execution I next continue to the next line, stepping over function calls I step continue to the next line, entering into subfunctions Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 410/526

1079. GDB graphical front-ends I DDD - Data Display Debugger http://www.gnu.org/software/ddd/ A popular graphical front-end, with advanced data plotting capabilities. I GDB/Insight http://sourceware.org/insight/ From the GDB maintainers. I KDbg http://www.kdbg.org/ Another front-end, for the K Display Environment. I Integration with other IDEs: Eclipse, Emacs, KDevelop, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 411/526

1080. Embedded Linux application development Remote debugging Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 412/526

1081. Remote debugging I In a non-embedded environment, debugging takes place using gdb or one of its front-ends. I gdb has direct access to the binary and libraries compiled with debugging symbols. I However, in an embedded context, the target platform environment is often too limited to allow direct debugging with gdb (2.4 MB on x86). I Remote debugging is preferred I gdb is used on the development workstation, oering all its features. I gdbserver is used on the target system (only 100 KB on arm). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 413/526

1082. Remote debugging: architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 414/526

1083. Remote debugging: usage I On the target, run a program through gdbserver. Program execution will not start immediately. gdbserver localhost:port executable args gdbserver /dev/ttyS0 executable args I Otherwise, attach gdbserver to an already running program: gdbserver --attach localhost:port pid I Then, on the host, run the ARCH-linux-gdb program, and use the following gdb commands: I To connect to the target: gdb target remote ip-addr:port (networking) gdb target remote /dev/ttyS0 (serial link) I To tell gdb where shared libraries are: gdb set sysroot library-path (without lib/) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 415/526

1084. Post mortem analysis I When an application crashes due to a segmentation fault and the application was not under control of a debugger, we get no information about the crash I Fortunately, Linux can generate a core

1085. le that contains the image of the application memory at the moment of the crash, and gdb can use this core

1086. le to let us analyze the state of the crashed application I On the target I Use ulimit -c unlimited to enable the generation of a core

1087. le when a crash occurs I On the host I After the crash, transfer the core

1088. le from the target to the host, and run ARCH-linux-gdb -c core-file application-binary Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 416/526

1089. Embedded Linux application development Memory checkers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 417/526

1090. DUMA Detect Unintended Memory Access http://duma.sourceforge.net/ I Fork and replacement for Electric Fence I Stops your program on the exact instruction that overruns or underruns a malloc() memory buer. I GDB will then display the source-code line that causes the bug. I Works by using the virtual-memory hardware to create a red-zone at the border of each buer - touch that, and your program stops. I Works on any platform supported by Linux, whatever the CPU (provided virtual memory support is available). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 418/526

1091. Valgrind (1) http://valgrind.org/ I GNU GPL Software suite for debugging and pro

1092. ling programs. I Supported platforms: Linux on x86, x86 64, ppc32, ppc64 and arm (armv7 only: Cortex A8, A9 and A5) I Can detect many memory management and threading bugs. I Pro

1093. ler: provides information helpful to speed up your program and reduce its memory usage. I The most popular tool for this usage. Even used by projects with hundreds of programmers. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 419/526

1094. Valgrind (2) I Can be used to run any program, without the need to recompile it. I Example usage Valgrind --leak-check=yes ls -la I Works by adding its own instrumentation to your code and then running in on its own virtual cpu core. Signi

1095. cantly slows down execution, but still

1096. ne for testing! I More details on http://valgrind.org/info/ and http://valgrind.org/docs/manual/ coregrind_core.html#howworks Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 420/526

1097. Embedded Linux application development System analysis Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 421/526

1098. strace System call tracer http://sourceforge.net/projects/strace/ I Available on all GNU/Linux systems Can be built by your cross-compiling toolchain generator. I Even easier: drop a ready-made static binary for your architecture, just when you need it. See http://git.free-electrons.com/users/michael-opdenacker/ static-binaries/tree/strace I Allows to see what any of your processes is doing: accessing

1099. les, allocating memory... Often sucient to

1100. nd simple bugs. I Usage: strace command (starting a new process) strace -p pid (tracing an existing process) See man strace for details. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 422/526

1101. strace example output strace cat Makefile execve(/bin/cat, [cat, Makefile], [/* 38 vars */]) = 0 brk(0) = 0x98b4000 access(/etc/ld.so.nohwcap, F_OK) = -1 ENOENT (No such file or directory) mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f85000 access(/etc/ld.so.preload, R_OK) = -1 ENOENT (No such file or directory) open(/etc/ld.so.cache, O_RDONLY) = 3 fstat64(3, {st_mode=S_IFREG|0644, st_size=111585, ...}) = 0 mmap2(NULL, 111585, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f69000 close(3) = 0 access(/etc/ld.so.nohwcap, F_OK) = -1 ENOENT (No such file or directory) open(/lib/tls/i686/cmov/libc.so.6, O_RDONLY) = 3 read(3, 177ELF11100000000030301000320h10004000344..., 512) = 512 fstat64(3, {st_mode=S_IFREG|0755, st_size=1442180, ...}) = 0 mmap2(NULL, 1451632, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7e06000 mprotect(0xb7f62000, 4096, PROT_NONE) = 0 mmap2(0xb7f63000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x15c) = 0xb7f63000 mmap2(0xb7f66000, 9840, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7f66000 close(3) = 0 Hint: follow the open

1102. le descriptors returned by open(). This tells you what

1103. les system calls are run on. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 423/526

1104. ltrace A tool to trace library calls used by a program and all the signals it receives I Very useful complement to strace, which shows only system calls. I Of course, works even if you don't have the sources I Allows to

1105. lter library calls with regular expressions, or just by a list of function names. I Manual page: http://linux.die.net/man/1/ltrace See http://en.wikipedia.org/wiki/Ltrace for details Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 424/526

1106. ltrace example output ltrace nedit index.html sscanf(0x8274af1, 0x8132618, 0x8248640, 0xbfaadfe8, 0) = 1 sprintf(const 0, const %d, 0) = 7 strcmp(startScan, const 0) = 1 strcmp(ScanDistance, const 0) = -1 strcmp(const 200, const 0) = 1 strcmp($list_dialog_button, const 0) = -1 strcmp($shell_cmd_status, const 0) = -1 strcmp($read_status, const 0) = -1 strcmp($search_end, const 0) = -1 strcmp($string_dialog_button, const 0) = -1 strcmp($rangeset_list, const 0) = -1 strcmp($calltip_ID, const 0) = -1 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 425/526

1107. ltrace summary Example summary at the end of the ltrace output (-c option) Process 17019 detached % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000050 50 1 set_thread_area 0.00 0.000000 0 48 read 0.00 0.000000 0 44 write 0.00 0.000000 0 80 63 open 0.00 0.000000 0 19 close 0.00 0.000000 0 1 execve 0.00 0.000000 0 2 2 access 0.00 0.000000 0 3 brk 0.00 0.000000 0 1 munmap 0.00 0.000000 0 1 uname 0.00 0.000000 0 1 mprotect 0.00 0.000000 0 19 mmap2 0.00 0.000000 0 50 46 stat64 0.00 0.000000 0 18 fstat64 ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000050 288 111 total Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 426/526

1108. OPro

1109. le http://oprofile.sourceforge.net I A system-wide pro

1110. ling tool I Can collect statistics like the top users of the CPU. I Works without having the sources. I Requires a kernel patch to access all features, but is already available in a standard kernel. I Requires more investigation to see how it works. I Ubuntu/Debian packages: oprofile, oprofile-gui Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 427/526

1111. Callgrind / KCachegrind I Cachegrind / Callgrind: part of the Valgrind tool suite Collects function call statistics and call graphs. Useful to know in which functions most time is spent. I KCachegrind: http://kcachegrind.sourceforge.net/ An amazing visualizer for Cachegrind / Callgrind data. I KCachegrind can also import data from other pro

1112. lers (such as OPro

1113. le), and from pro

1114. ling output from Python, Perl and PHP. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 428/526

1115. KCachegrind screenshot Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 429/526

1116. Practical lab - App. development and debugging Application development I Compile your own application with the ncurses library Remote debugging I Set up remote debugging tools on the target: strace, ltrace and gdbserver. I Debug a simple application running on the target using remote debugging Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 430/526

1117. Embedded Linux application development Developing on Windows Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 431/526

1118. Developing on Windows!? Using a GNU/Linux workstation is the easiest way to create software for GNU/Linux or embedded Linux I You use the same tools and environment as all community developers do. Much fewer issues you are the only one to face. I You get familiar with the system. Essential for understanding issues. However, some developers have no choice: Windows is the only desktop OS allowed in their company. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 432/526

1119. Cygwin http://cygwin.com/ Linux (POSIX)-like environment for Windows I 2 components: Linux API emulation layer: cygwin1.dll A collection of tools originally found in GNU/Linux I Allows to compile and run many GNU/Linux programs on Windows: shells, compiler, http servers, X Window, GTK... I Very easy to install. Can choose which tools to download and install. I For embedded Linux system developers: makes it possible to use GNU toolchains (compiled for Windows) required to build Linux binaries (kernel, libraries or applications). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 433/526

1120. Cygwin limitations Cygwin is not a complete substitute for a real GNU/Linux system. I Almost all developers work on GNU/Linux or on another Unix platform (typically BSD). Don't expect them to test that their tools build on Windows with Cygwin. I The number of Cygwin users is quite small. You may be the

1121. rst to face or report building issues on this platform for a given compiler or tool version. I Cygwin is very slow. So, the best solution is to run Linux inside Windows! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 434/526

1122. VMware http://en.wikipedia.org/wiki/VMware I License: proprietary I Can run a GNU/Linux PC from Windows, almost at the host speed. I VMware Player is now available free of charge. Many Free Software system images available for download. The most popular solution in the corporate world. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 435/526

1123. VirtualBox http://virtualbox.org from Oracle I PC emulation solution available on both Windows and GNU/Linux I 2 licenses: I Proprietary: free of cost for personal use and evaluation. Binaries available for Windows. Full features. I Open Source Edition (OSE): GPL license. Most features (except in particular USB support). No binaries released for Windows so far (but possible). I Based on QEMU's core engine. Performance similar to that of VMware. See http://en.wikipedia.org/wiki/VirtualBox Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 436/526

1124. Real-time in embedded Linux systems Real-time in embedded Linux systems Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 437/526

1125. Real-time in embedded Linux systems Introduction Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 438/526

1126. Embedded Linux and real time I Due to its advantages, Linux and open-source software are more and more commonly used in embedded applications I However, some applications also have real-time constraints I They, at the same time, want to I Get all the nice advantages of Linux: hardware support, components re-use, low cost, etc. I Get their real-time constraints met Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 439/526

1127. Embedded Linux and real time I Linux is an operating system part of the large Unix family I It was originally designed as a time-sharing system I The main goal was to get the best throughput from the available hardware, by making the best possible usage of resources (CPU, memory, I/O) I Time determinism was not taken into account I On the opposite, real-time constraints imply time determinism, even at the expense of lower global throughput I Best throughput and time determinism are contradictory requirements Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 440/526

1128. Linux and real-time approaches (1) I Over time, two major approaches have been taken to bring real-time requirements into Linux I Approach 1 I Improve the Linux kernel itself so that it matches real-time requirements, by providing bounded latencies, real-time APIs, etc. I Approach taken by the mainline Linux kernel and the PREEMPT RT project. I Approach 2 I Add a layer below the Linux kernel that will handle all the real-time requirements, so that the behaviour of Linux doesn't aect real-time tasks. I Approach taken by RTLinux, RTAI and Xenomai Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 441/526

1129. Linux and real-time approaches (2) An alternative approach is to use speci

1130. c hardware to run real-time work on: I Dedicating a CPU core to a real-time OS or to a real-time application, using some kind of hypervizor. I Running real-time work on an FPGA I Running real-time work on a dedicated microcontroller. For example, the TI AM335x CPU (used in the Beaglebone Black) has a Programmable Real-Time Unit and Industrial Communication Subsystem (PRU-ICSS), which can be used for real-time processing. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 442/526

1131. Real-time in embedded Linux systems Improving the main Linux kernel with PREEMPT RT Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 443/526

1132. Understanding latency I When developing real-time applications with a system such as Linux, the typical scenario is the following I An event from the physical world happens and gets noti

1133. ed to the CPU by means of an interrupt I The interrupt handler recognizes and handles the event, and then wake-up the user space task that will react to this event I Some time later, the user space task will run and be able to react to the physical world event I Real-time is about providing guaranteed worst case latencies for this reaction time, called latency Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 444/526

1134. Linux kernel latency components kernel latency = interrupt latency + handler duration + scheduler latency + scheduler duration Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 445/526

1135. Interrupt latency Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 446/526

1136. Sources of interrupt latency I One of the concurrency prevention mechanism used in the kernel is the spinlock I It has several variants, but one of the variant commonly used to prevent concurrent accesses between a process context and an interrupt context works by disabling interrupts I Critical sections protected by spinlocks, or other section in which interrupts are explicitly disabled will delay the beginning of the execution of the interrupt handler I The duration of these critical sections is unbounded I Other possible source: shared interrupts Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 447/526

1137. Interrupt handler duration Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 448/526

1138. Interrupt handler implementation I In Linux, many interrupt handlers are split in two parts I A top-half, started by the CPU as soon as interrupts are enabled. It runs with the interrupt line disabled and is supposed to complete as quickly as possible. I A bottom-half, scheduled by the top-half, which starts after all pending top-halves have completed their execution. I Therefore, for real-time critical interrupts, bottom-halves shouldn't be used: their execution is delayed by all other interrupts in the system. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 449/526

1139. Scheduler latency Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 450/526

1140. Understanding preemption (1) I The Linux kernel is a preemptive operating system I When a task runs in user space mode and gets interrupted by an interruption, if the interrupt handler wakes up another task, this task can be scheduled as soon as we return from the interrupt handler. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 451/526

1141. Understanding preemption (2) I However, when the interrupt comes while the task is executing a system call, this system call has to

1142. nish before another task can be scheduled. I By default, the Linux kernel does not do kernel preemption. I This means that the time before which the scheduler will be called to schedule another task is unbounded. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 452/526

1143. Scheduler duration Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 453/526

1144. Other non-deterministic mechanisms I Outside of the critical path detailed previously, other non-deterministic mechanisms of Linux can aect the execution time of real-time tasks I Linux is highly based on virtual memory, as provided by an MMU, so that memory is allocated on demand. Whenever an application accesses code or data for the

1145. rst time, it is loaded on demand, which can creates huge delays. I Many C library services or kernel services are not designed with real-time constraints in mind. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 454/526

1146. Priority inversion A process with a low priority might hold a lock needed by a higher priority process, eectively reducing the priority of this process. Things can be even worse if a middle priority process uses the CPU. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 455/526

1147. Interrupt handler priority In Linux, interrupt handlers are executed directly by the CPU interrupt mechanisms, and not under control of the Linux scheduler. Therefore, all interrupt handlers have a higher priority than all tasks running on the system. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 456/526

1148. The PREEMPT RT project I Long-term project lead by Linux kernel developers Ingo Molnar, Thomas Gleixner and Steven Rostedt I https://rt.wiki.kernel.org I The goal is to gradually improve the Linux kernel regarding real-time requirements and to get these improvements merged into the mainline kernel I PREEMPT RT development works very closely with the mainline development I Many of the improvements designed, developed and debugged inside PREEMPT RT over the years are now part of the mainline Linux kernel I The project is a long-term branch of the Linux kernel that ultimately should disappear as everything will have been merged Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 457/526

1149. Improvements in the mainline kernel I Coming from the PREEMPT RT project I Since the beginning of 2.6 I O(1) scheduler I Kernel preemption I Better POSIX real-time API support I Since 2.6.18 I Priority inheritance support for mutexes I Since 2.6.21 I High-resolution timers I Since 2.6.30 I Threaded interrupts I Since 2.6.33 I Spinlock annotations Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 458/526

1150. New preemption options in Linux 2.6 2 new preemption models oered by standard Linux 2.6: Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 459/526

1151. 1st option: no forced preemption CONFIG_PREEMPT_NONE Kernel code (interrupts, exceptions, system calls) never preempted. Default behavior in standard kernels. I Best for systems making intense computations, on which overall throughput is key. I Best to reduce task switching to maximize CPU and cache usage (by reducing context switching). I Still bene

1152. ts from some Linux 2.6 improvements: O(1) scheduler, increased multiprocessor safety (work on RT preemption was useful to identify hard to

1153. nd SMP bugs). I Can also bene

1154. t from a lower timer frequency (100 Hz instead of 250 or 1000). Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 460/526

1155. 2nd option: voluntary kernel preemption CONFIG_PREEMPT_VOLUNTARY Kernel code can preempt itself I Typically for desktop systems, for quicker application reaction to user input. I Adds explicit rescheduling points throughout kernel code. I Minor impact on throughput. I Used in: Ubuntu Desktop 13.04, Ubuntu Server 12.04 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 461/526

1156. 3rd option: preemptible kernel CONFIG_PREEMPT Most kernel code can be involuntarily preempted at any time. When a process becomes runnable, no more need to wait for kernel code (typically a system call) to return before running the scheduler. I Exception: kernel critical sections (holding spinlocks). In a case you hold a spinlock on a uni-processor system, kernel preemption could run another process, which would loop forever if it tried to acquire the same spinlock. I Typically for desktop or embedded systems with latency requirements in the milliseconds range. I Still a relatively minor impact on throughput. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 462/526

1157. Priority inheritance I One classical solution to the priority inversion problem is called priority inheritance I The idea is that when a task of a low priority holds a lock requested by a higher priority task, the priority of the

1158. rst task gets temporarily raised to the priority of the second task: it has inherited its priority. I In Linux, since 2.6.18, mutexes support priority inheritance I In user space, priority inheritance must be explicitly enabled on a per-mutex basis. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 463/526

1159. High resolution timers I The resolution of the timers used to be bound to the resolution of the regular system tick I Usually 100 Hz or 250 Hz, depending on the architecture and the con

1160. guration I A resolution of only 10 ms or 4 ms. I Increasing the regular system tick frequency is not an option as it would consume too many resources I The high-resolution timers infrastructure, merged in 2.6.21, allows to use the available hardware timers to program interrupts at the right moment. I Hardware timers are multiplexed, so that a single hardware timer is sucient to handle a large number of software-programmed timers. I Usable directly from user space using the usual timer APIs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 464/526

1161. Threaded interrupts I To solve the interrupt inversion problem, PREEMPT RT has introduced the concept of threaded interrupts I The interrupt handlers run in normal kernel threads, so that the priorities of the dierent interrupt handlers can be con

1162. gured I The real interrupt handler, as executed by the CPU, is only in charge of masking the interrupt and waking-up the corresponding thread I The idea of threaded interrupts also allows to use sleeping spinlocks (see later) I Merged since 2.6.30, the conversion of interrupt handlers to threaded interrupts is not automatic: drivers must be modi

1163. ed I In PREEMPT RT, all interrupt handlers are switched to threaded interrupts Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 465/526

1164. The future of the PREEMPT RT patchset Conclusion of the Realtime Linux minisummit (Nov. 2013): I The PREEMPT RT project will be done in 2014, one way or another. The

1165. rst way would be to get most of the rest of the code upstream, but that will require more of an eort, from a wider group than is currently involved. The alternative is to decide that the 95% of the realtime work already upstream is good enough and to drop further eorts. I Main issue: lack of companies devoting enough engineering resources to complete the job. I See http://lwn.net/Articles/572740/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 466/526

1166. Real-time in embedded Linux systems PREEMPT RT speci

1167. cs Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 467/526

1168. CONFIG PREEMPT RT (1) I The PREEMPT RT patch adds a new level of preemption, called CONFIG_PREEMPT_RT I This level of preemption replaces all kernel spinlocks by mutexes (or so-called sleeping spinlocks) I Instead of providing mutual exclusion by disabling interrupts and preemption, they are just normal locks: when contention happens, the process is blocked and another one is selected by the scheduler. I Works well with threaded interrupts, since threads can block, while usual interrupt handlers could not. I Some core, carefully controlled, kernel spinlocks remain as normal spinlocks. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 468/526

1169. CONFIG PREEMPT RT (2) I With CONFIG_PREEMPT_RT, virtually all kernel code becomes preemptible I An interrupt can occur at any time, when returning from the interrupt handler, the woken up process can start immediately. I This is the last big part of PREEMPT RT that isn't fully in the mainline kernel yet I Part of it has been merged in 2.6.33: the spinlock annotations. The spinlocks that must remain as spinning spinlocks are now dierentiated from spinlocks that can be converted to sleeping spinlocks. This has reduced a lot the PREEMPT RT patch size! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 469/526

1170. Threaded interrupts I The mechanism of threaded interrupts in PREEMPT RT is still dierent from the one merged in mainline I In PREEMPT RT, all interrupt handlers are unconditionally converted to threaded interrupts. I This is a temporary solution, until interesting drivers in mainline get gradually converted to the new threaded interrupt API that has been merged in 2.6.30. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 470/526

1171. Real-time in embedded Linux systems Setting up PREEMPT RT Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 471/526

1172. PREEMPT RT setup (1) I PREEMPT RT is delivered as a patch against the mainline kernel I Best to have a board supported by the mainline kernel, otherwise the PREEMPT RT patch may not apply and may require some adaptations I At the moment, only even releases of the Linux kernel are supported: 3.0, 3.2, 3.4, 3.6, 3.8, 3.10, 3.12, 3.14. I Quick set up I Download the latest PREEMPT RT patch from http://www.kernel.org/pub/linux/kernel/projects/rt/ I Download and extract the corresponding mainline kernel version I Apply the patch to the mainline kernel tree Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 472/526

1173. PREEMPT RT setup (2) I In the kernel con

1174. guration, be sure to enable I CONFIG_PREEMPT_RT I High-resolution timers I Compile your kernel, and boot I You are now running the real-time Linux kernel I Of course, some system con

1175. guration remains to be done, in particular setting appropriate priorities to the interrupt threads, which depend on your application. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 473/526

1176. Real-time in embedded Linux systems Real-time application development with PREEMPT RT Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 474/526

1177. Development and compilation I No special library is needed, the POSIX real-time API is part of the standard C library I The glibc or eglibc C libraries are recommended, as support for some real-time features is not available in uClibc yet I Priority inheritance mutexes or NPTL on some architectures, for example I Compile a program I ARCH-linux-gcc -o myprog myprog.c -lrt I To get the documentation of the POSIX API I Install the manpages-posix-dev package I Run man function-name Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 475/526

1178. Process, thread? I Confusion about the terms process, thread and task I In Unix, a process is created using fork() and is composed of I An address space, which contains the program code, data, stack, shared libraries, etc. I One thread, that starts executing the main() function. I Upon creation, a process contains one thread I Additional threads can be created inside an existing process, using pthread_create() I They run in the same address space as the initial thread of the process I They start executing a function passed as argument to pthread_create() Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 476/526

1179. Process, thread: kernel point of view I The kernel represents each thread running in the system by a structure of type task_struct I From a scheduling point of view, it makes no dierence between the initial thread of a process and all additional threads created dynamically using pthread_create() Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 477/526

1180. Creating threads I Linux support the POSIX thread API I To create a new thread pthread_create(pthread_t *thread, pthread_attr_t *attr, void *(*routine)(void*), void *arg); I The new thread will run in the same address space, but will be scheduled independently I Exiting from a thread pthread_exit(void *value_ptr); I Waiting for the termination of a thread pthread_join(pthread_t *thread, void **value_ptr); Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 478/526

1181. Scheduling classes (1) I The Linux kernel scheduler support dierent scheduling classes I The default class, in which processes are started by default is a time-sharing class I All processes, regardless of their priority, get some CPU time I The proportion of CPU time they get is dynamic and aected by the nice value, which ranges from -20 (highest) to 19 (lowest). Can be set using the nice or renice commands I The real-time classes SCHED_FIFO and SCHED_RR I The highest priority process gets all the CPU time, until it blocks. I In SCHED_RR, round-robin scheduling between the processes of the same priority. All must block before lower priority processes get CPU time. I Priorities ranging from 0 (lowest) to 99 (highest) Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 479/526

1182. Scheduling classes (2) I An existing program can be started in a speci

1183. c scheduling class with a speci

1184. c priority using the chrt command line tool I Example: chrt -f 99 ./myprog I The sched_setscheduler() API can be used to change the scheduling class and priority of a process int sched_setscheduler(pid_t pid, int policy, const struct sched_param *param); I policy can be SCHED_OTHER, SCHED_FIFO, SCHED_RR, etc. I param is a structure containing the priority Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 480/526

1185. Scheduling classes (3) I The priority can be set on a per-thread basis when a thread is created struct sched_param parm; pthread_attr_t attr; pthread_attr_init(attr); pthread_attr_setinheritsched(attr, PTHREAD_EXPLICIT_SCHED); pthread_attr_setschedpolicy(attr, SCHED_FIFO); parm.sched_priority = 42; pthread_attr_setschedparam(attr, parm); I Then the thread can be created using pthread_create(), passing the attr structure. I Several other attributes can be de

1186. ned this way: stack size, etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 481/526

1187. Memory locking I In order to solve the non-determinism introduced by virtual memory, memory can be locked I Guarantee that the system will keep it allocated I Guarantee that the system has pre-loaded everything into memory I mlockall(MCL_CURRENT | MCL_FUTURE); I Locks all the memory of the current address space, for currently mapped pages and pages mapped in the future I Other, less useful parts of the API: munlockall, mlock, munlock. I Watch out for non-currently mapped pages I Stack pages I Dynamically-allocated memory Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 482/526

1188. Mutexes I Allows mutual exclusion between two threads in the same address space I Initialization/destruction pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr); pthread_mutex_destroy(pthread_mutex_t *mutex); I Lock/unlock pthread_mutex_lock(pthread_mutex_t *mutex); pthread_mutex_unlock(pthread_mutex_t *mutex); I Priority inheritance must be activated explicitly pthread_mutexattr_t attr; pthread_mutexattr_init (attr); pthread_mutexattr_setprotocol(attr, PTHREAD_PRIO_INHERIT); Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 483/526

1189. Timers I Timer creation timer_create(clockid_t clockid, struct sigevent *evp, timer_t *timerid); I clockid is usually CLOCK_MONOTONIC. sigevent de

1190. nes what happens upon timer expiration: send a signal or start a function in a new thread. timerid is the returned timer identi

1191. er. I Con

1192. gure the timer for expiration at a given time timer_settime(timer_t timerid, int flags, struct itimerspec *newvalue, struct itimerspec *oldvalue); Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 484/526

1193. Timers (2) I Delete a timer timer_delete(timer_t timerid) I Get the resolution of a clock, clock_getres I Other functions: timer_getoverrun(), timer_gettime() Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 485/526

1194. Signals I Signals are asynchronous noti

1195. cation mechanisms I Noti

1196. cation occurs either I By the call of a signal handler. Be careful with the limitations of signal handlers! I By being unblocked from the sigwait(), sigtimedwait() or sigwaitinfo() functions. Usually better. I Signal behaviour can be con

1197. gured using sigaction() I The mask of blocked signals can be changed with pthread_sigmask() I Delivery of a signal using pthread_kill() or tgkill() I All signals between SIGRTMIN and SIGRTMAX, 32 signals under Linux. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 486/526

1198. Inter-process communication I Semaphores I Usable between dierent processes using named semaphores I sem_open(), sem_close(), sem_unlink(), sem_init(), sem_destroy(), sem_wait(), sem_post(), etc. I Message queues I Allows processes to exchange data in the form of messages. I mq_open(), mq_close(), mq_unlink(), mq_send(), mq_receive(), etc. I Shared memory I Allows processes to communicate by sharing a segment of memory I shm_open(), ftruncate(), mmap(), munmap(), close(), shm_unlink() Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 487/526

1199. Real-time in embedded Linux systems Debugging latencies in PREEMPT RT Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 488/526

1200. ftrace - Kernel function tracer Infrastructure that can be used for debugging or analyzing latencies and performance issues in the kernel. I Very well documented in Documentation/trace/ftrace.txt I Negligible overhead when tracing is not enabled at run-time. I Can be used to trace any kernel function! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 489/526

1201. Using ftrace I Tracing information available through the debugfs virtual fs (CONFIG_DEBUG_FS in the Kernel Hacking section) I Mount this

1202. lesystem as follows: mount -t debugfs nodev /sys/kernel/debug I When tracing is enabled (see the next slides), tracing information is available in /sys/kernel/debug/tracing. I Check available tracers in /sys/kernel/debug/tracing/available_tracers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 490/526

1203. Scheduling latency tracer CONFIG_SCHED_TRACER (Kernel Hacking section) I Maximum recorded time between waking up a top priority task and its scheduling on a CPU, expressed in us. I Check that wakeup is listed in /sys/kernel/debug/tracing/available_tracers I To select, reset and enable this tracer: echo wakeup /sys/kernel/debug/tracing/current_tracer echo 0 /sys/kernel/debug/tracing/tracing_max_latency echo 1 /sys/kernel/debug/tracing/tracing_enabled I Let your system run, in particular real-time tasks. Dummy example: chrt -f 5 sleep 1 I Disable tracing: echo 0 /sys/kernel/debug/tracing/tracing_enabled I Read the maximum recorded latency and the corresponding trace: cat /sys/kernel/debug/tracing/tracing_max_latency Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 491/526

1204. Exemple of worst-case latencies Tests done with cyclictest I x86 Geode 500 Mhz: 96 us I x86 Pentium Dual-core T4500 2.3 Ghz: 36 us I ARM Freescale i.MX35 533 Mhz: 120 us I ARM Marvell 88FR131 1200 Mhz: 54 us See more results at https://www.osadl.org/QA-Farm- Realtime.qa-farm-about.0.html Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 492/526

1205. Useful reading About real-time support in the standard Linux kernel I Inside the RT patch, Steven Rostedt, Red Hat, ELC 2013 http://elinux.org/images/b/ba/Elc2013_Rostedt.pdf Video: http://j.mp/1apUtu6 I The Real-Time Linux Wiki: http://rt.wiki.kernel.org The Wiki Web for the CONFIG PREEMPT RT community, and real-time Linux in general. Contains nice and useful documents! I See also our books page. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 493/526

1206. Real-time in embedded Linux systems Real-time extensions to the Linux kernel Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 494/526

1207. Linux real-time extensions Three generations I RTLinux I RTAI I Xenomai A common principle I Add an extra layer between the hardware and the Linux kernel, to manage real-time tasks separately. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 495/526

1208. RTLinux First real-time extension for Linux, created by Victor Yodaiken. I Nice, but the author

1209. led a software patent covering the addition of real-time support to general operating systems as implemented in RTLinux! I Its Open Patent License drew many developers away and frightened users. Community projects like RTAI and Xenomai now attract most developers and users. I February, 2007: RTLinux rights sold to Wind River. Today, no longer advertised by Wind River. I Project completely dead. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 496/526

1210. RTAI http://www.rtai.org/ - Real-Time Application Interface for Linux I Created in 1999, by Prof. Paolo Mantegazza (long time contributor to RTLinux), Dipartimento di Ingegneria Aerospaziale Politecnico di Milano (DIAPM). I Community project. Signi

1211. cant user base. Attracted contributors frustrated by the RTLinux legal issues. I Only really actively maintained on x86 I May oer slightly better latencies than Xenomai, at the expense of a less maintainable and less portable code base I Since RTAI is not really maintained on ARM and other embedded architectures, our presentation is focused on Xenomai. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 497/526

1212. Xenomai project http://www.xenomai.org/ I Started in 2001 as a project aiming at emulating traditional RTOS. I Initial goals: facilitate the porting of programs to GNU / Linux. I Initially related to the RTAI project (as the RTAI / fusion branch), now independent. I Skins mimicking the APIs of traditional RTOS such as VxWorks, pSOS+, and VRTXsa as well as the POSIX API, and a native API. I Aims at working both as a co-kernel and on top of PREEMPT RT in future upstream Linux versions. I Will never be merged in the mainline kernel. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 498/526

1213. Xenomai architecture Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 499/526

1214. The Adeos interrupt pipeline abstraction I From the Adeos point of view, guest OSes are prioritized domains. I For each event (interrupts, exceptions, syscalls, etc...), the various domains may handle the event or pass it down the pipeline. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 500/526

1215. Xenomai features I Factored real-time core with skins implementing various real-time APIs I Seamless support for hard real-time in user space I No second-class citizen, all ports are equivalent feature-wise I Xenomai support is as much as possible independent from the Linux kernel version (backward and forward compatible when reasonable) I Each Xenomai branch has a stable user/kernel ABI I Timer system based on hardware high-resolution timers I Per-skin time base which may be periodic I RTDM skin allowing to write real-time drivers Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 501/526

1216. Xenomai user space real-time support I Xenomai supports real-time in user space on 5 architectures, including 32 and 64 bits variants. I Two modes are de

1217. ned for a thread I the primary mode, where the thread is handled by the Xenomai scheduler I the secondary mode, when it is handled by the Linux scheduler. I Thanks to the services of the Adeos I-pipe service, Xenomai system calls are de

1218. ned. I A thread migrates from secondary mode to primary mode when such a system call is issued I It migrates from primary mode to secondary mode when a Linux system call is issued, or to handle gracefully exceptional events such as exceptions or Linux signals. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 502/526

1219. Life of a Xenomai application I Xenomai applications are started like normal Linux processes, they are initially handled by the Linux scheduler and have access to all Linux services I After their initialization, they declare themselves as real-time applications, which migrates them to primary mode. In this mode: I They are scheduled directly by the Xenomai scheduler, so they have the real-time properties oered by Xenomai I They don't have access to any Linux service, otherwise they get migrated back to secondary mode and loose all real-time properties I They can only use device drivers that are implemented in Xenomai, not the ones of the Linux kernel I Need to implement device drivers in Xenomai, and to split real-time and non real-time parts of your applications. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 503/526

1220. Real Time Driver Model (RTDM) I An approach to unify the interfaces for developing device drivers and associated applications under real-time Linux I An API very similar to the native Linux kernel driver API I Allows to develop in kernel space: I Character-style device drivers I Network-style device drivers I See the whitepaper on http://www.xenomai.org/documentation/xenomai- 2.6/pdf/RTDM-and-Applications.pdf I Current notable RTDM based drivers: I Serial port controllers; I RTnet UDP/IP stack; I RT socket CAN, drivers for CAN controllers; I Analogy, fork of the Comedi project, drivers for acquisition cards. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 504/526

1221. Real-time in embedded Linux systems Setting up Xenomai Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 505/526

1222. How to build Xenomai I Download Xenomai sources at http://download.gna.org/xenomai/stable/ I Download one of the Linux versions supported by this release (see ksrc/arch/arch/patches/) I Since version 2.0, split kernel/user building model. I Kernel uses a script called script/prepare-kernel.sh which integrates Xenomai kernel-space support in the Linux sources. I Run the kernel con

1223. guration menu. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 506/526

1224. Linux options for Xenomai con

1226. Xenomai user space support I User space libraries are compiled using the traditional autotools I ./configure --host=arm-linux make make DESTDIR=/your/rootfs/ install I Xenomai installs pkg-con

1227. g

1228. les which helps you to compile your own programs against the Xenomai libraries. I See Xenomai's examples directory. I Installation details may be found in the README.INSTALL guide. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 508/526

1229. Real-time in embedded Linux systems Developing applications on Xenomai Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 509/526

1230. The POSIX skin I The POSIX skin allows to recompile without changes a traditional POSIX application so that instead of using Linux real-time services, it uses Xenomai services I http://www.xenomai.org/index.php/Porting_POSIX_ applications_to_Xenomai I Clocks and timers, condition variables, message queues, mutexes, semaphores, shared memory, signals, thread management I Good for existing code or programmers familiar with the POSIX API I Of course, if the application uses any Linux service that isn't available in Xenomai, it will switch back to secondary mode I To link an application against the POSIX skin CFL=pkg-config --cflags libxenomai_posix LDF=pkg-config --libs libxenomai_posix ARCH-gcc $CFL -o rttest rttest.c $LDF Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 510/526

1231. Communication with a normal task I If a Xenomai real-time application using the POSIX skin wishes to communicate with a separate non-real-time application, it must use the rtipc mechanism I In the Xenomai application, create an IPCPROTO_XDDP socket socket(AF_RTIPC, SOCK_DGRAM, IPCPROTO_XDDP); setsockopt(s, SOL_RTIPC, XDDP_SETLOCALPOOL, poolsz, sizeof(poolsz)); memset(saddr, 0, sizeof(saddr)); saddr.sipc_family = AF_RTIPC; saddr.sipc_port = PORTX; ret = bind(s, (struct sockaddr *)saddr, sizeof(saddr)); I And then the normal socket API sendto() / recvfrom() I In the Linux application I Open /dev/rtpPORTX, where PORTX is the XDDP port I Use read() and write() Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 511/526

1232. The native API (1) I A Xenomai speci

1233. c API for developing real-time tasks I http://xenomai.org/documentation/branches/v2.4.x/ pdf/Native-API-Tour-rev-C.pdf I Usable both in user space and kernel space. Development of tasks in user space is the preferred way. I More coherent and more exible API than the POSIX API. Easier to learn and understand. Certainly the way to go for new applications. I Applications should include native/service.h, where service can be alarm, buffer, cond, event, heap, intr, misc, mutex, pipe, queue, sem, task, timer I To compile applications: CFL=pkg-config --cflags libxenomai_native LDF=pkg-config --libs libxenomai_native ARCH-gcc $CFL -o rttest rttest.c $LDF Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 512/526

1234. The native API (2) I Task management services I rt_task_create(), rt_task_start(), rt_task_suspend(), rt_task_resume(), rt_task_delete(), rt_task_join(), etc. I Counting semaphore services I rt_sem_create(), rt_sem_delete(), rt_sem_p(), rt_sem_v(), etc. I Message queue services I rt_queue_create(), rt_queue_delete(), rt_queue_alloc(), rt_queue_free(), rt_queue_send(), rt_queue_receive(), etc. I Mutex services I rt_mutex_create(), rt_mutex_delete(), rt_mutex_acquire(), rt_mutex_release(), etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 513/526

1235. The native API (3) I Alarm services I rt_alarm_create(), rt_alarm_delete(), rt_alarm_start(), rt_alarm_stop(), rt_alarm_wait(), etc. I Memory heap services I Allows to share memory between processes and/or to pre-allocate a pool of memory I rt_heap_create(), rt_heap_delete(), rt_heap_alloc(), rt_heap_bind() I Condition variable services I rt_cond_create(), rt_cond_delete(), rt_cond_signal(), rt_cond_broadcast(), rt_cond_wait(), etc. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 514/526

1236. Xenomai and normal task communication I Using rt pipes I In the native Xenomai application, use the Pipe API I rt_pipe_create(), rt_pipe_delete(), rt_pipe_receive(), rt_pipe_send(), rt_pipe_alloc(), rt_pipe_free() I In the normal Linux application I Open the corresponding /dev/rtpX

1237. le, the minor is speci

1238. ed at rt_pipe_create() time I Then, just read() and write() to the opened

1240. Xenomai worst-case latencies results I ARM OMAP5432 1.1 GHz: 24 us I ARM OMAP4430 1 GHz: 29 us I ARM OMAP3530 720 MHz: 41 us I ARM AT91SAM9263 180 MHz: 108 us I ARM AT91RM9200 180 MHz: 181 us I x86 Atom 1.6 GHz: 31 us I Geode LX800 processor at 500 MHz: 49 us See results at http://xenomai.org/~gch/core-3.10-latencies/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 516/526

1241. Books Building Embedded Linux Systems, O'Reilly By Karim Yaghmour, Jon Masters, Gilad Ben-Yossef, Philippe Gerum and others (including Michael Opdenacker), August 2008 A nice coverage of Xenomai (Philippe Gerum) and the RT patch (Steven Rostedt) http://oreilly.com/catalog/9780596529680/ Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 517/526

1242. Organizations I http://www.realtimelinuxfoundation.org/ Community portal for real-time Linux. Organizes a yearly workshop. I http://www.osadl.org Open Source Automation Development Lab (OSADL) Targets machine and plant control systems. Most member companies are German (Thomas Gleixner is on board). Supports the use of PREEMPT RT and Xenomai and contributes to these projects. Shares useful documentation and resources. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 518/526

1243. Practical lab - Real-time - Scheduling latency I Check clock accuracy. I Start processes with real-time priority. I Build a real-time application against the standard POSIX real-time API, and against Xenomai's POSIX skin I Compare scheduling latency on your system, between a standard kernel and a kernel with Xenomai. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 519/526

1244. References References Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 520/526

1245. Books I Embedded Linux Primer, Second Edition, Prentice Hall By Christopher Hallinan, October 2010 Covers a very wide range of interesting topics. http://j.mp/17NYxBP I Building Embedded Linux Systems, O'Reilly By Karim Yaghmour, Jon Masters, Gilad Ben-Yossef, Philippe Gerum and others (including Michael Opdenacker), August 2008 http://oreilly.com/catalog/9780596529680/ I Embedded Linux System Design and Development P. Raghavan, A. Lad, S. Neelakandan, Auerbach, Dec. 2005. Very good coverage of the POSIX programming API (still up to date). http://j.mp/19X8iu2 Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 521/526

1246. Web sites I ELinux.org, http://elinux.org, a Wiki entirely dedicated to embedded Linux. Lots of topics covered: real-time,

1247. lesystem, multimedia, tools, hardware platforms, etc. Interesting to explore to discover new things. I LWN, http://lwn.net, very interesting news site about Linux in general, and speci

1248. cally about the kernel. Weekly newsletter, available for free after one week for non-paying visitors. I Linux Gizmos, http://linuxgizmos.com, a news site about embedded Linux, mainly oriented on hardware platforms related news. Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 522/526

1249. International conferences Useful conferences featuring embedded Linux and kernel topics I Embedded Linux Conference: http://embeddedlinuxconference.com/ Organized by the Linux Foundation: California (San Francisco, Spring), in Europe (Fall). Very interesting kernel and user space topics for embedded systems developers. Presentation slides freely available I Linux Plumbers, http://linuxplumbersconf.org Conference on the low-level plumbing of Linux: kernel, audio, power management, device management, multimedia, etc. I FOSDEM: http://fosdem.org (Brussels, February) For developers. Presentations about system development. I Don't miss our free conference videos on http://free-electrons. com/community/videos/conferences/! Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 523/526

1250. Last slides Last slides Free Electrons ©Copyright 2004-2014, Free Electrons. Creative Commons BY-SA 3.0 license. Corrections, suggestions, contributions and translations are welcome! Embedded Linux Developers Free Electrons Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 524/526

1251. Evaluation form Please take a few minutes to rate this training session, by answering our on-line survey: http://free-electrons.com/doc/training/embedded-linux/survey.html Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 525/526

1252. Last slide Thank you! And may the Source be with you Free Electrons - Embedded Linux, kernel, drivers and Android - Development, consulting, training and support. http://free-electrons.com 526/526

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