Building your own embedded system with Yocto

Building your own embedded
system with Yocto

13.03.2020Building your own embedded system with Yocto • Marius Meisenzahl
Preface
● if you have any questions, don't hesitate to ask, comment, ...
● ⚠ 10 GB of free disk space ⚠
● ⚠ internet connection ⚠
● please pass the USB ﬂash drives around and copy the contents to your
laptop
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🙋‍♂ About me
● Marius Meisenzahl
● loves to tinker with hardware and software 🤓
● Linux enthusiast 🐧
● co-founder of
○ located in Bochum
○ we build software from embedded to web
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/meisenzahl /msnzhl

🐧 Linux origin story
● ﬁrst steps with Knoppix, Mandriva (formerly Mandrake)
● distro hopped: openSUSE, Debian, Ubuntu, Arch Linux, ...
○ interest in how things work
■ Gentoo
■ Linux From Scratch → Great for a rainy weekend
● Ubuntu Hardy Heron (8.04)
● several years Arch Linux
● for a long time elementary OS (Ubuntu based distribution)
● building own systems
○ Kernel + BusyBox
○ Buildroot
○ Yocto
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Quick Poll
● Who of you has ever built an embedded system before?
● Who of you has ever compiled a Linux kernel?
● Who of you has ever used a cross-compiler?
5

Goals
➔ Building your own embedded system with Yocto
◆ How do embedded Linux systems work?
◆ What is Yocto?
◆ How does Yocto work?
6

Agenda
1. Basic knowledge
○ Embedded systems
○ Yocto Project
2. Inner workings
○ Initial setup
○ Leaving the comfort zone
3. Getting used to it
○ DIY
○ Outlook
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1. Basic knowledge
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Embedded systems
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What is an embedded system?
● An embedded system is a computer system that has a dedicated function
within a larger mechanical or electrical system
● A distribution is an operating system based on a Linux kernel
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Architecture of embedded systems
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Applications
Libraries
System Call Interface
IO
Management
Process
Management
Memory
Management
Device Driver Layer
Bootloader
Firmware
Userland
Kernel
Hardware
ConﬁgurationsApplications

Hardware
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Firmware
● basic initialization of the hardware
● loads the bootloader
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Bootloader
● further initialization of the hardware
● loads kernel and userland into main memory
● additional features
○ read and write memory
○ deﬁne boot parameters
○ choose boot source (internal/external memory, network, …)
○ scripting (A/B booting, …)
○ image veriﬁcation
○ ...
● common bootloader
○ Das U-Boot
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Kernel
15
System Call Interface
IO
Management
Process
Management
Memory
Management
Device Driver Layer
Kernel

Kernel
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Kernel
● current LTS 5.4.25
○ allnoconﬁg 652 KB
○ allyesconﬁg 123 MB
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Kernel
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Userland
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Applications
LibrariesConfigurations
Userland
● logic of the system apart from the kernel
● located on root file system
● contains
○ libraries
○ applications
○ configurations
○ …
Applications

Userland
● kernel starts process with id 1
○ so called init process
● it can be a simple shell script
○ which starts other processes
● or a full blown process manager like systemd
○ starts so called services as background processes
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Userland
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init
pid=1
httpd
pid=1038
login
pid=154
bash
pid=294
httpd
pid=1364
httpd
pid=1284
ls
pid=336
cowsay
pid=300
php
pid=1783
php
pid=1694
htop
pid=385

Filesystem Hierarchy Standard (simplified)
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/bin, /sbin system applications
/boot boot related files like kernels, ...
/dev, /proc, /sys devices, processes, ...
/etc configuration files
/home user related files
/lib libraries
/tmp temporary files
/usr user applications, libraries, ...

Yocto Project
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It’s not an embedded Linux distribution.
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It’s not an embedded Linux distribution.
It creates a custom one for you.
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Yocto
● open source project of the Linux Foundation
● licensed under MIT and GPLv2
● helps developers create custom Linux-based systems regardless of the
hardware architecture
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Poky
● Poky is the reference distribution
● you can use it as a base
● tweak it to your needs
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Cooking
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👨‍🍳
🍛
🍚🥕🧂🍠
📗📘📙
📄

Engineering with Yocto
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👨‍🍳 👨‍💻
🍛 embedded system
🍚🥕🧂🍠 libraries, applications, ...
📗📘📙 📁 layers
📄 📄 recipe

Layers
📁 meta-embo
📁 meta-poky
📁 meta-selftest
📁 meta-skeleton
📁 meta-yocto-bsp
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Layer
meta-embo
├── conf
│ ├── distro
│ │ ├── embo.conf
│ │ └── embo-tiny.conf
│ └── layer.conf
└── recipes-core
├── hello-cmake
│ └── hello-cmake.bb
└── images
└── embo-image.bb
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BBPATH .= ":${LAYERDIR}"
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb
${LAYERDIR}/recipes-*/*/*.bbappend"
BBFILE_COLLECTIONS += "embo"
BBFILE_PATTERN_embo = "^${LAYERDIR}/"
BBFILE_PRIORITY_embo = "6"
LAYERSERIES_COMPAT_embo = "warrior"

Recipe
meta-embo
├── conf
└── images
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DESCRIPTION = "hello cmake"
SECTION = "examples"
LICENSE = "CLOSED"
DEPENDS = ""
SRC_URI = " file:./hello-cmake/"
S = "${WORKDIR}/hello-cmake"
inherit pkgconfig cmake

Image
meta-embo
├── conf
└── images
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require recipes-core/images/core-image-minimal.bb
IMAGE_INSTALL_append = "
hello-cmake
hello-make
hello-meson
"

BitBake
● build tool
● reads .bb and .bbappend ﬁles
● resolves dependencies between recipes
● creates build order
● generates Python code to build packages
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BitBake tasks
● fetch
● unpack
● patch
● configure
● compile
● populate
● install
● package
● package_write
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2. Inner workings
37

Initial setup
38

QEMU
● generic machine emulator and virtualizer
● licensed under GPLv2 and BSD
● we use qemu-system-i386 to test our embedded system
○ due to lack of embedded hardware
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👷 Build Host
● linux distribution
○ Windows Subsystem for Linux (WSL) is not supported
○ but you can use Docker or a virtual machine (VirtualBox)
● Ubuntu 16.04, 18.04, 19.04
● Fedora 28, 29, 30
● CentOS 7.x
● Debian GNU/Linux 8.x, 9.x, 10.x
● OpenSUSE Leap 15.1
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👷 Build Host
● initialize your build environment
○ Docker (recommended)
○ local (Linux only)
○ VirtualBox
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🤞 Test if build environment works
● make embo-image
● make run-embo-image
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Important ﬁles and folders
● Makeﬁle
○ BRANCH
○ DISTRO
○ MACHINE
● poky/build/conf/bblayers.conf
● poky/build/conf/local.conf
○ DL_DIR = downloads
○ SSTATE_DIR = sstate-cache
● poky/build/tmp/deploy/images
● poky/build/tmp/deploy/licenses
● poky/build/tmp/deploy/rpm
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👨‍💻

Playtime
● login as user root
● ps
○ /init pid=1
● /init
○ /sbin/init
■ /bin/busybox.nosuid
● /bin/busybox.nosuid
● /bin/busybox.nosuid init
● hello-make
● hello-cmake
● hello-meson
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👨‍💻

hello-make
● minimal example built with make
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👨‍💻

hello-cmake
● minimal example built with cmake
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👨‍💻

hello-meson
● minimal example built with meson
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👨‍💻

Leaving the comfort zone
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bitbake
● cd poky
● source oe-init-build-env
● export DISTRO=embo-tiny
● export MACHINE=qemux86
● bitbake embo-image
● bitbake hello-make -c build
● bitbake hello-make -c cleanall
● bitbake hello-make -c build
● bitbake -s
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👨‍💻

Dependencies
🔗 https://layers.openembedded.org/layerindex/branch/warrior/recipes/
● git clone -b warrior git:./git.openembedded.org/meta-openembedded
● add to poky/build/conf/bblayers.conf
○ meta-openembedded/meta-oe
● bitbake nlohmann-json
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👨‍💻

hello-json
● create a new example recipe which uses nlohmann-json
DESCRIPTION = "hello json"
LICENSE = "CLOSED"
DEPENDS = "nlohmann-json"
SRC_URI = " file:./hello-json/"
S = "${WORKDIR}/hello-json"
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👨‍💻

hello-json
● create a main.cpp which uses nlohmann-json
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann.:json;
int main() {
json j;
j["hello"] = "json";
std.:cout .< j.dump() .< std.:endl;
return 0;
}
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👨‍💻

hello-json
● create a CMakeLists.txt to build example
cmake_minimum_required(VERSION 3.10)
project(hello-json)
find_package(nlohmann_json REQUIRED)
add_executable(hello-json main.cpp)
target_link_libraries(hello-json nlohmann_json.:nlohmann_json)
install(TARGETS hello-json DESTINATION bin)
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👨‍💻

embo-image
● add your new package to our image
require recipes-core/images/core-image-minimal.bb
IMAGE_INSTALL_append = "
hello-cmake
hello-make
hello-meson
hello-json
"
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👨‍💻

embo-image
● bitbake embo-image
● make run-embo-image
● hello-json
○ {"hello":"json"}
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👨‍💻

Dependency graph
● bitbake -g hello-make
● less recipe-depends.dot
● ⚠ dot -Tpng recipe-depends.dot -o recipe-depends.png ⚠
● less task-depends.dot
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👨‍💻

Dependency graph
● bitbake -g embo-image
● less recipe-depends.dot
● less task-depends.dot
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👨‍💻

3. Getting used to it
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Add ﬁles to rootfs
base-ﬁles_%.bbappend
FILESEXTRAPATHS_prepend .= "${THISDIR}/files:"
SRC_URI += "file:./embo"
do_install_append() {
install -m 0644 ${WORKDIR}/embo ${D}/embo
}
59

Add users
recipe
inherit useradd
USER .= "user"
PASSWORD .= "9PfNy0O1z0O5g"
USERADD_PACKAGES = "${PN}"
USERADD_PARAM_${PN} = ".-system .-create-home
.-groups tty
.-password ${PASSWORD}
.-user-group ${USER}"
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⚠ DISTRO = embo ⚠

hello-boost
DESCRIPTION = "hello boost"
LICENSE = "CLOSED"
DEPENDS = "boost"
RDEPENDS_${PN} = "boost-thread"
SRC_URI = " file:./hello-boost/"
S = "${WORKDIR}/hello-boost"
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hello-boost
#include <boost/thread.hpp>
#include <boost/chrono.hpp>
#include <iostream>
void wait(int seconds) {
boost.:this_thread.:sleep_for(boost.:chrono.:seconds{seconds});
}
void thread() {
for (int i = 0; i < 5; .+i) {
wait(1);
std.:cout .< i .< std.:endl;
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}
}
int main() {
boost.:thread t{thread};
t.join();
return 0;
}

hello-boost
cmake_minimum_required(VERSION 3.10)
project(hello-boost)
find_package(Boost COMPONENTS thread REQUIRED)
add_executable(hello-boost main.cpp)
include_directories(${Boost_INCLUDE_DIRS})
target_link_libraries(hello-cmake ${Boost_LIBRARIES})
install(TARGETS hello-boost DESTINATION bin)
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DIY
● try to build something yourself
● ask for help
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Outlook
● bundle sources of packages used to build image
○ update your systems with a package manager
■ EXTRA_IMAGE_FEATURES += "package-management"
○ sign your packages
■ INHERIT += "sign_rpm"
● create a SDK to simplify development
○ bitbake <image> -c populate_sdk
● bundle list of licenses of packages used to build image
● license management
○ prohibit certain licenses
■ INCOMPATIBLE_LICENSE = "GPL-3.0 LGPL-3.0 AGPL-3.0"
● ...
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What else can you do with Yocto?
● build custom Docker images
IMAGE_FSTYPES += " .tar.gz"
FROM scratch
ADD rootfs.tar.gz /
CMD ["/bin/sh"]
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References
● https://www.yoctoproject.org/docs/current/mega-manual/mega-manual.h
tml
● https://git.yoctoproject.org/
● https://www.yoctoproject.org/docs/what-i-wish-id-known/
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