Basics of Embedded Software, Lecture notes of Microprocessors

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>>> Basics of Embedded Softwares

Name: Neil Robert Membreve, M.Eng. Date:

Department of Electrical Engineering

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>>> Motivation

■ How does code get converted into

ones and zeroes?

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>>> Embedded Software Modules

■ The software is organized in layers ■ Each layer assumes specific functionality ■ Modules are described in C-files (.c) ■ Definitions are described in header files (.h) ■ Functions interact with other modules ■ Eventually interact with Hardware Figure: Layers of an embedded system software

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>>> Embedded System Software Layers

■ Device Drivers ■ Interface to hardware layers ■ Hardware Abstraction Layer (HAL) ■ Code Booting ■ Real-time operation system (RTOS) ■ Abstracts High from Low levels ■ Scheduling ■ Resource management ■ Libraries for shared code

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>>> Embedded Programming Languages

Figure: Top embedded programming languages

ASPENCORE. (2017). 2017 Embedded Markets Study Integrating IoT and Advanced Technology Designs, Application Development & Processing Environments. April, 1-

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>>> Why C?

■ Availability of compilers for almost any MCU ■ Small executable ■ Deterministic resource use (e.g., no dynamic memory allocation) ■ Efficient Memory Management ■ Timing-centric operations ■ Direction Hardware/IO Control ■ Optimized execution

Figure: C can be used even on very small micro-controllers

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>>> Embedded Software Development Processs

Figure: Computer and target processor

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>>> Embedded Software Development Processs

Figure: Software tools

The software tools include compiler toolchain (e.g., AVR GCC, gdb make files), linker, emulators, simulators, SDK, text editors/IDE, version control, etc

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>>> Embedded Software Development Processs

Figure: The role of a preprocessor

The C preprocessor is the macro preprocessor for the C compiler. The preprocessor provides the ability for the inclusion of header files, macro expansions, conditional compilation, and line control.

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>>> Embedded Software Development Processs

Figure: The role of a linker

The linker combines all of the object files into a single executable object code, which uses symbols to reference other functions/variables

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>>> Code Compilation using GNU Toolsets

■ A computer only understand a set of instructions in a numeric format, typically called machine code

1 # include < stdio .h > 2 3 int main () { 4 printf ( " Hello , World! " ) ; 5 return 0; 6 } Listing 1: Source code

Figure: Machine code

■ The GCC compiler - The GNU Compiler Collection^1 - is often used for compilating embedded system. (^1) https://www3.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html

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>>> Code Compilation using GNU Toolsets

■ First stage of the compilation process ■ Removes all the comments ■ Include any #include files (typical the .h header file) ■ Expands all the macros

1 gcc -E hello. c > hello. i

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>>> Translation of C code into machine code

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>>> Translation of C code into machine code

1 Pre-processing - via the AVR GNU C Preprocessor (avr-cpp), which includes the headers (#include) and expands the macros (#define). avr-cpp -mmcu=attiny13 blink.c > blink.i The resultant intermediate file blink.i contains the expanded source code. 2 Compilation - the compiler compiles the pre-processed source code into assembly code for a specific processor. avr-gcc -S blink.i >blink.s The -S option specifies to produce assembly code, instead of object code. The resultant assembly file is "blink.s". 3 Assembly - the assembler (avr-as) converts the assembly code into machine code in the object file "hello.o" avr-as -o blink.o blink.s

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