Module-3 embedded system firmware code.ppt
- 2. • responsible for controlling the various peripherals of the embedded hardware • stored in a permanent memory (ROM)
- 3. Designing Embedded firmware • requires understanding of the particular embedded product hardware, • like various component interfacing, • memory map details, • I/O port details, • configuration and register details of various hardware chips used and • some programming language (either low level Assembly Language or High level language like C/C++ or a combination of the two)
- 4. There exist two basic approaches for the design and implementation of embedded firmware, namely; The Super loop based approach The Embedded Operating System based approach The decision on which approach needs to be adopted for firmware development is purely dependent on the complexity and system requirements
- 5. Embedded firmware Design Approaches – The Super loop Suitable for applications that are not time critical Very similar to a conventional procedural programming where the code is executed task by task The tasks are executed in a never ending loop. A typical super loop implementation will look like: 1. Configure the common parameters and perform initialization for various hardware components memory, registers etc. 2. Start the first task and execute it 3. Execute the second task 4. Execute the next task 5. : 6. : 7. Execute the last defined task 8. Jump back to the first task and follow the same flow
- 6. void main () { Configurations (); Initializations (); While (1) { Task 1 (); Task 2 (); //: //: Task n (); } } The only way to come out of this loop is either hardware reset or an interrupt assertion
- 7. Embedded firmware Design Approaches – Embedded OS based Approach The embedded device contains an Embedded Operating System which can be one of: • A Real Time Operating System (RTOS) • A Customized General Purpose Operating System (GPOS) • The Embedded OS is responsible for scheduling the execution of user tasks and the allocation of system resources among multiple tasks • Involves lot of OS related overheads apart from managing and executing user defined tasks
- 8. Microsoft® Windows XP Embedded is an example of GPOS for embedded devices Point of Sale (PoS) terminals, Gaming Stations, Tablet PCs etc are examples of embedded devices running on embedded GPOSs ‘Windows CE’, ‘Windows Mobile’,‘QNX’, ‘VxWorks’, ‘ThreadX’, ‘MicroC/OS-II’, ‘Embedded Linux’, ‘Symbian’ etc are examples of RTOSs employed in Embedded Product development Mobile Phones, PDAs, Flight Control Systems etc are examples of embedded devices that runs on RTOSs
- 9. Embedded firmware Development Languages/Options Assembly Language High Level Language Subset of C (Embedded C) Subset of C++ (Embedded C++) Any other high level language with supported Cross- compiler Mix of Assembly & High level Language Mixing High Level Language (Like C) with Assembly Code Mixing Assembly code with High Level Language (Like C) Inline Assembly
- 10. Embedded firmware Development Languages/Options – Assembly Language Assembly Language’ is the human readable notation of ‘machine language’ ‘machine language’ is a processor understandable language Machine language is a binary representation and it consists of 1s and 0s • Assembly language programming is the process of writing processor specific machine code in mnemonic form, converting the mnemonics into actual processor instructions (machine language) and associated data using an assembler
- 11. The general format of an assembly language instruction is an Opcode followed by Operands The Opcode tells the processor/controller what to do and the Operands provide the data and information required to perform the action specified by the opcode Each line of an assembly language program is split into four fields as: LABEL OPCODE OPERAND COMMENTS
- 12. ;#################################################################### ; SUBROUTINE FOR GENERATING DELAY ; DELAY PARAMETR PASSED THROUGH REGISTER R1 ; RETURN VALUE NONE ; REGISTERS USED: R0, R1 ;#################################################################### DELAY: MOV R0, #255 ; Load Register R0 with 255 DJNZ R1, DELAY ; Decrement R1 and loop till R1= 0 RET ; Return to calling program
- 13. • The Assembly language program written in assembly code is saved as .asm (Assembly file) file or a .src (source) file or a format supported by the assembler • The software utility called ‘Assembler’ performs the translation of assembly code to machine code • Assembling of each source file generates a corresponding object file. The object file does not contain the absolute address of where the generated code needs to be placed (a re-locatable code) on the program memory • The software program called linker/locater is responsible for assigning absolute address to object files during the linking process • A software utility called ‘Object to Hex file converter’ translates the absolute object file to corresponding hex file (binary file)
- 14. Embedded firmware Development Languages/Options – Assembly Language – Source File to Hex File Translation Assembly language to machine language Conversion process
- 15. Embedded firmware Development Languages/Options – High Level Language • The embedded firmware is written in any high level language like C, C++ • A software utility called ‘cross-compiler’ converts the high level language to target processor specific machine code • The cross-compilation of each module generates a corresponding object file. The object file does not contain the absolute address of where the generated code needs to be placed (a re-locatable code) on the program memory • The software program called linker/locater is responsible for assigning absolute address to object files during the linking process • A software utility called ‘Object to Hex file converter’ translates the absolute object file to corresponding hex file (binary file)
- 16. Embedded firmware Development Languages/Options – High Level Language – Source File to Hex File Translation Source File 1 (.c /.c++ etc) (Module-1) Module Cross-compiler Source File 2 (.c /.c++ etc) (Module-2) Module Cross-compiler Object File 1 Object File 2 Library Files Linker/ Locator Absolute Object File Object to Hex File Converter Machine Code (Hex File) High level language to machine language conversion process
- 17. Embedded firmware Development Languages/Options – Mixing of Assembly Language with High Level Language Certain situations in Embedded firmware development may require the mixing of Assembly Language with high level language or vice versa. Interrupt handling, Source code is already available in high level language Assembly Language etc are examples High Level language and low level language can be mixed in three different ways Mixing Assembly Language with High level language like ‘C’ Mixing High level language like ‘C’ with Assembly Language In line Assembly The passing of parameters and return values between the high level and low level language is cross-compiler specific
- 18. High Level Language – ‘C’ V/s Embedded C Embedded C can be considered as a subset of conventional ‘C’ language Embedded C supports all ‘C’ instructions and incorporates a few target processor specific functions/instructions The standard ANSI ‘C’ library implementation is always tailored to the target processor/controller library files in Embedded C The implementation of target processor/controller specific functions/instructions depends upon the processor/controller as well as the supported cross-compiler for the particular Embedded C language A software program called ‘Cross-compiler’ is used for the conversion of programs written in Embedded C to target processor/controller specific instructions
- 19. High Level Language Based Development – ‘Compiler’ V/s ‘Cross-Compiler’ Compiler is a software tool that converts a source code written in a high level language on top of a particular operating system running on a specific target processor architecture (E.g. Intel x86/Pentium). The operating system, the compiler program and the application making use of the source code run on the same target processor. The source code is converted to the target processor specific machine instructions A native compiler generates machine code for the same machine (processor) on which it is running. Cross compiler is the software tools used in cross-platform development applications In cross-platform development, the compiler running on a particular target processor/OS converts the source code to machine code for a target processor whose architecture and instruction set is different from the processor on which the compiler is running or for an operating system which is different from the current development environment OS Embedded system development is a typical example for cross-platform development where embedded firmware is developed on a machine with Intel/AMD or any other target processors and the same is converted into machine code for any other target processor architecture (E.g. 8051, PIC, ARM9 etc). Keil C51compiler from Keil software is an example for cross-compiler for 8051 family architecture
- 20. Programming in Embedded C
- 26. THANK YOU