BoSs

Bare operating System solution

Project of OS core for ARM Cortex-M3 microcontrollers with emulation on Qemu.

Implements preemptive multitasking scheduller. Also provides lightweight object oriented hardware abstraction framework.

Aimed for quick and easy development of efficient applications on resource restricted MCUs.

Currently supported:

• STM32F103 series

Project structure

• bin - binary output files
• build - cmake build directory; contains compile_commands.json used for IntelliSense support
• docs - usefull documentation and books
• libs - 3rd party libraries
• scripts - workflow automation scripts
• sources - source code

Project variants

Standart Cpp libraries support

There are two variants to copmile the project possible and handled with Cmake CACHE variable use_libg.

1. Maximal lightweight project - Set use_libg OFF. Doesn't use any libc or libg. So size of application scratch is about 2kB only. Link with -nostdlib flag. Compile with -fno-exceptions -fno-non-call-exceptions -fno-rtti -fno-use-cxa-atexit flags. .ARM.extab & .ARM.exidx sections have to be discarded, so special linker script linkerSectionsNoExc.ld is used.
2. C++ 17 and STL full support - Set use_libg ON. Use libg_nano with semihosting turned OFF. Add modern C++ features like exceptions, RTTI, std::function and so on. Minimal size will grow to about 10kB. Compile with no additional flags. .ARM.extab & .ARM.exidx sections have to be included to binary, so linkerSections.ld script is used.

Destination target

There are two targets to copmile the project possible and handled with Cmake CMAKE_BUILD_TYPE and use_qemu_dummies variables.

1. QEMU - Set CMAKE_BUILD_TYPE Debug. Option use_qemu_dummies handles usage of special code for QEMU and turns ON for Debug target automaticaly. Otherwise has to be turned ON in Cmake cache manually.
2. STM32 real hardware - Set CMAKE_BUILD_TYPE to any other type except Debug. Option use_qemu_dummies has to be turned OFF.

Used tools

• arm-none-eabi - GCC based toolchain for project compilation and linkage.
• GCC - Compilers collection used for UnitTests building.
• make - Buid utility.
• cmake/ctest - Build generation system. Building and testing automation.
• googleTest - Unit testing framework.
• OpenOCD - Real hardware debug and uploading/downloading firmaware onto developement board.
• stm32flash - Uploading/downloading firmaware onto developement board. Communication with default stm32 bootloader.
• GDB - Debug.

Last builds size

• STM32 bare metal without std libs: Flash - 2024 bytes, RAM - 8+20 bytes
• STM32 bare metal with std libg_nano: Flash - 14280 bytes, RAM - 124+88 bytes

To Do

• Clean project from garbage
• Create Linker script and normal startup with Vectors table to run on Qemu
• Simple Threads primitive to Run
• Write context switch procedure
• Check if threads run
• Create PendingSV handler on ASM - problem that C++ handler procedure saves some registers on stack each run
• Unit tests
• two configs for QEMU and for REAL HW
• reafact added files. create few target configurations for qemuDebug and realHW
• target for CMSIS, and chose correct startup procedures
• real hardware start
• qemu DWT not implemented?
• Context switch procedures profiling. Use DWT
• lambda use
• Scheduler must also set nextThread pointer
• target for libC or not? use standart libC and exceptions? write manual
• #pragma once use and delete uint32_t where is not needed
• look like wrong thread SP in PendSV- problem was in std::function
• Refactoring of PendSV - integrate pause and ctxt save to switchThread()
• write unit tests of scheduler
• update time on delete from TimersQueue
• try to simplify sleepSysCall
• rename svCallMock and proxy classes
• SLEEPING threads queue
• create vscode cmake build configuration
• update doks
• embed 3rd party libs using cmake
• Context switch optimisation for 1 thread case
• Thread SLEEP()
• Divide to namespaces
• Mutex and semafore
• cppCheck static analisis
• Self test with semafore and poling systimer
• Make user treads to run in Unprivileged mode and one thread for kernel tasks. Run user main() from _init. before this go to PSP unprivileged mode.
• Stack Overflow detection by "endmarks"
• try to delete dependencies to LL lib .cpp and other trash
• delete from Framework headers #includes of STM LL and CMSIS. Make them pure interface headers. This will require some atribute types redefinition.