Embedded Software Fundamentals - How does code get ...

Embedded SoftwareFundamentals

How does code get converted into ones and zeroes?

Kizito NKURIKIYEYEZU,Ph.D.

Reading materialRead the following resources available on the course platforms

1 Chapter 1 of White, E. (2011). Making Embedded Systems:Design Patterns for Great Software. " O’Reilly Media, Inc.".

2 Chapter 3 of Bertolotti, I. C., & Hu, T. (2017). Embedded SoftwareDevelopment. Amsterdam University Press.

Kizito NKURIKIYEYEZU, Ph.D. Embedded Software Fundamentals September 26, 2021 1 / 22


Components of embeddedsoftware development

Host MachineDevelopmentEnvironmentsCompiler ToolchainDebuggersDevelopment KitsVersion Control

FIG 1. Components of an embeddeddevelopment


Modules of a typical embeddedsoftware

The software is organized inlayersEach layer assumes specificfunctionalityModules are described inC-files (.c)Definitions are described inheader files (.h)Functions interact with othermodulesEventually interact withHardware

FIG 2. Layers of an embedded systemsoftware


Embedded system software inlayers

Device DriversInterface to hardwarelayersHardware AbstractionLayer (HAL)

Code BootingReal-time operation system(RTOS)

Abstracts High from LowlevelsSchedulingResource management

Libraries for shared codeKizito NKURIKIYEYEZU, Ph.D. Embedded Software Fundamentals September 26, 2021 5 / 22

Hardware Abstraction

Low level and bare-MetalFirmwareHardware Abstraction LayerPlatform IndependenceHigh quality and portablesoftware

MaintainableTestablePortableRobustEfficientConsistent


Embedded programminglanguages

FIG 3. Top embedded programming languagesASPENCORE. (2017). 2017 Embedded Markets Study Integrating IoT andAdvanced Technology Designs, Application Development & ProcessingEnvironments. April, 1–102.


Why C?

Availability of compilers for almostany MCUSmall executableDeterministic resource use (e.g.,no dynamic memory allocation)Efficient Memory ManagementTiming-centric operationsDirection Hardware/IO ControlOptimized executionNote: Modern C++ is as efficientas C and I believe it will slowlyreplace C in the future. For detailssee Kormanyos, C. (2018).Real-time C++: efficientobject-oriented and templatemicrocontroller programming

FIG 4. C can be used even onvery small micro-controllersThe ATtiny20-UUR is an AVRmicro-controller that is smallerthan a grain of rice. It is an8-Bit IC that runs at 12MHz2KB (1K x 16) FLASH and12-WLCSP (1.56x1.4)


Embedded softwaredevelopment process

FIG 5. Embedded System Development PlatformThe host machine contains the build environment for an embedded system. Itcontains a cross compiler and a cross debugger. The debug allowscommunication between the target processor through a special processorinterface, the JTAG


FIG 6. Computer and target processor


FIG 7. Software toolsThe software tools include compiler toolchain (e.g., AVR GCC, gdb make files),linker, emulators, simulators, SDK, text editors/IDE, version control, etc


FIG 8. Detailed embedded C compilation processThe C preprocessor transform the program before actual compilation. Thecompiler translate the source code into opcode (object files) for the targetprocessor. The linker combine these object files and resolve all of theunresolved symbols. The locator assign physical memory addresses to each ofthe code and data and produce an output file containing a binary memoryimage that can be loaded into the target ROM.


FIG 9. The role of a preprocessorThe C preprocessor is the macro preprocessor for the C compiler. Thepreprocessor provides the ability for the inclusion of header files, macroexpansions, conditional compilation, and line control.


FIG 10. The role of a linkerThe linker combines all of objects files into a single executable object codeuses symbols to reference other functions/variables


FIG 11. Linear detailed embedded C compilation processThe compiler translate the source code into opcode (object files) for the targetprocessor. The linker combine these object files and resolve all of theunresolved symbols. The locator assign physical memory addresses to each ofthe code and data and produce an output file containing a binary memoryimage that can be loaded into the target ROM.

Kizito NKURIKIYEYEZU, Ph.D. Embedded Software Fundamentals September 26, 2021 15 / 22 Kizito NKURIKIYEYEZU, Ph.D. Embedded Software Fundamentals September 26, 2021 16 / 22

Introduction to BuildSystems using AVR GNU

Toolsets

Translation of C code into machinecode

:0C000000B89A91E088B3892788BBFCCF38:00000001FF


Translation of C code into machinecodeGCC compiles a C/C++ program into executable in 4 steps:

1 Pre-processing—via the AVR GNU C Preprocessor(avr-cpp), which includes the headers (#include) andexpands the macros (#define).

avr-cpp -mmcu=attiny13 blink.c > blink.iThe resultant intermediate file blink.i contains the expandedsource code.

2 Compilation—the compiler compiles the pre-processedsource code into assembly code for a specific processor.

avr-gcc -S blink.i >blink.sThe -S option specifies to produce assembly code, instead ofobject code. The resultant assembly file is "blink.s".

3 Assembly —the assembler (avr-as) converts the assemblycode into machine code in the object file "hello.o".

avr-as -o blink.o blink.sKizito NKURIKIYEYEZU, Ph.D. Embedded Software Fundamentals September 26, 2021 18 / 22

Translation of C code into machinecode

4 Linker: Finally, the linker links the object code with the librarycode to produce an executable and linkable format (.elf) file"blink.elf".

avr-gcc blink.o -o blink.elfThis generates an .elf file isn’t directly executable by theMCU. Thus, one needs to extract the machine code from it inthe Intel Hex format

avr-objcopy -O ihex -R .eeprom blink.elf blink.ihexNotes:

You can see the detailed compilation process by enabling -v(verbose) option. For example,

avr-gcc -v -mmcu=attiny13 -o blink.bin blink.cYou can Generate all intermidiate files

avr-gcc -mmcu=attiny13 -save-temps blink.cYou should always enable optimization with the -Osparameter

avr-gcc -v -Os -mmcu=attiny13 -save-temps blink.c


Building automation

The need for building automation

Building can be tediousMany GCC flagsMany independentcommandsMany build targetsMany supportedarchitecturesMany source files

Building manually cancause consistency issueswaste development time

Real world software iscomplex. For example, theLinux kernel contains:

More than 23,000 .c filesMore than 18,000 headerfileMore than 1,400assembly filesHow would you compilerthis manually?

In most cases, one can usean Integrated developmentenvironment (IDE) toautomate this process.

Why use an automatic build system?Build Management Software (or Build Automation) provides asimple and consistent method for producing a target executable


Build Management Software

Automated the process ofPreprocessingAssemblingCompilingLinkingRelocatingUpload the machine codeto the microcontroller

GNU Toolset performs alloperations using makeReal world make files arecomplex1, but are oftenpreferred to using IDE2

1https://www.gnu.org/software/make/manual/html_node/Complex-Makefile.html2https://www.embeddedrelated.com/showthread/comp.arch.embedded/252000-1.php


Example make file


https://www.gnu.org/software/make/manual/html_node/Complex-Makefile.html

https://www.embeddedrelated.com/showthread/comp.arch.embedded/252000-1.php

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