Hi,

we have an initial page for porting in our handbook: https://docs.mbed.com/docs/mbed-os-handbook/en/latest/advanced/porting_guide/

We use targets, publicly they are seen as boards. They are based on MCU targets. A board defines pinout (PinNames, Peripheral pins), default clock setup + board setup, and applications for the board (examples). MCU has own target but that is not exposed, as it is a base target (class that you can build your board). You should be able to quickly create a board based on the targets that are already supported. For instance, https://github.com/ARMmbed/mbed-os/blob/master/targets/targets.json#L949, that defines NUCLEO F303RE. If you need 303, but a different pinout (smaller package, bigger), different clocks, etc. Create a new target and set it up according to this (https://github.com/ARMmbed/mbed-os/tree/master/targets/TARGET_STM/TARGET_STM32F3 - this is F3 targets, each of them contains subfolders with detailed pinout, peripheral, linker file, startup file). This is described in the handbook porting guide. Any feedback appreciated to make this process easier.

You can change in the online compiler or offline (using mbed-cli) a target quickly, and your app should work (if pinnames and peripheral pins match, in this case is good to use for instance arduino pins Ax, D0 that would allow this). Please clone https://github.com/ARMmbed/mbed-os-example-blinky, blinky example, do targets change you need, export or compile locally to test your changes.

Some exporters need additional setup, that needs porting. Therefore not all targets support all exporters. For instance, MDK exporter uses cmsis-pack for device, if it is not there, it wont be supported.

Thank you for the links and steps, i'll have a new try this afternoon

Well, this is what i've already done of course https://github.com/Hoel/mbed/tree/master/mbed-dev/targets/TARGET_STM I based the custom target on the existing DISCO STM32F303VC folder. It took a lot of changes and once compiling after a long strike it has been tried with blinky example, unfortunately the STM32F303CC falls in <UsageFault_Handler> when reaching HAL_TIM_SET_COMPARE(&TimMasterHandle, TIM_CHANNEL_1, (uint32_t)timestamp); function is situated in the file : us_ticker_32b.c

If there was a tool to make this folders and files set automatically when providing a target MCU as argument that would ease things a lot, doing this by hand is error prone and we dont have all the elements to do it properly (startup and linker files), since mbed uses the STM32 HAL it should tailor to any STM32 target.

ST has some specific settings, hal_tick.h in this case plus cmsis_nvic.h (these 2 need to be tailored for your target).

Also look at the startup file, I recall by default they had main jump, not _start as it is required by mbed (true for GCC only) that you are using

Thanks for the hint, indeed i suspected cmsis_nvic.h has specific setting, however i cannot find the appropriate informations for my target. I counted 82 + 15 vectors but i am really unsure of this figure nor if NVIC_RAM_VECTOR_ADDRESS 0x20000000 is actually the right address, same goes for hal_tick.h. For startup file i use the one from AC6 (SW4STM32) and it doesnt seem to have not _start https://github.com/Hoel/mbed/blob/master/STM32F303CC_LED_HAL_MBED/src/targets/TARGET_STM/TARGET_STM32F3/TARGET_STM32F303xC/device/TOOLCHAIN_GCC_ARM/startup_stm32.s