cshark_test

About

CSHARK Recruitment task - Reading sensor data using freeRTOS

The project is intended to be build on Linux machine ( preferably Ubuntu 24.04 LTS )

I use the NUCLEO-G431RB board from ST as a host MCU platform. The sensor I'm about to read ain't real (Couldn't find anything interesting at home). I simply emulate it on the serial port on PC with basic python script. The sensor gets single byte data request from MCU 0xAA, and responds with host PC CPU temperature ( float ) followed by the 8-bit CRC. Underlying uart interface is configured in simples blocking mode.

Firmware functionality as described in requirements: Two FreeRTOS tasks. One for reading and one for processing the data. Data exchanged between tasks through the rtos queue. Data post processing is a simple "moving average" mechanism.

More info

• Custom CMake-based build system that handles cross-compilation and native unit test build as well
• Negligible usage of CubeMX generated code
• Using original freeRTOS repository ( not the one provided with Cube package or generated by MX )
• RTOS, MCU package and unit test frameworks are a submodules in this repository
• Cpputest framework for unit testing
• Development under MS Visual Studio Code with extensive usage of CMake tools extensions for the IDE configuration

Must have

I'm not going to list all prerequisites here... Assuming that arm-none-eabi-gcc, CMake, Make, Binutils etc. are installed...

( only once ) Fetch Submodules ( CppuTest, Cube G4, freeRTOS-kernel ) git submodule update --init --recursive --depth=1

Build firmware

1. Configure Cmake

cmake -B ./build_firmware -DCMAKE_BUILD_TYPE:STRING=Debug -DTARGET_PLATFORM:STRING=EMBEDDED -DCMAKE_TOOLCHAIN_FILE:FILEPATH=cmake/gcc-arm-none-eabi.cmake .

2. Build

cmake --build ./build_firmware

3. Flash target

STM32_Programmer_CLI -c port=swd -D ./build/Debug-EMBEDDED/cshark_test.elf -rst

Build unit tests ( Sensor unit tests example provided )

1. Configure Cmake

cmake -B ./build_unit_tests -DCMAKE_BUILD_TYPE:STRING=Debug -DTARGET_PLATFORM:STRING=UNIT_TESTS .

2. Build

cmake --build ./build_unit_tests

3. Run unit test executables

./build/Debug-UNIT_TESTS/test_runners/test_sensor_test_suite -v -b

Testing strategy ( conceptual )

• All data processing methods should be covered by unit tests to ensure their proper operation.
• All interfaces ( or other dependencies ) should use a dependency injection pattern and should be mocked when used in unit tests ( example provided )
• Integration tests for processes cooperation should be provided
• Manual testing of device functionality
• Regression prevention should be covered by the automatic tests building and running in CI pipeline

Improvements ideas

• Separate module for CRC calculation and use of G4 CRC peripheral for faster calculation
• Improved uart class to make use of interrupts and/or DMA and a better error handling and race condition prevention.
• (as above) make use of RTOS mutexes to prevent collisions when accessing physical interfaces from multiple threads
• Create bootloader and implement runtime firmware upgrade ability ( preferably secureBoot concept )
• Analyze the risc of error occurrence in the business logic code and provide a robust handling

Theoretical CI/CD stages

1. Checking the code against standards / formatting (clang-format, cppcheck, etc...)
2. Building the production code (cross compilation before tests as there is no sense to run unit tests if the target code does not build well)
3. Building the testing code
4. Running tests
5. Post processing ( binary files encryption, generating crypto keys, etc...)
6. Storing artifacts and build log files
7. Deployment binary artifacts to production server / device where multiple devices could be flashed