Add STM32 support

[BrechtSerckx]

Hi! Thanks for the project!

I added support for STM32 boards with built-in CAN controller using https://github.com/pazi88/STM32_CAN.
As far as I can see, the example seems to work with my ODrive S1 and Adafruit STM32F405 Feather Express.

Please note that I am not comfortable with C++ programming, please let me know of any improvements I can make.

Thanks!

[CLAassistant]

All committers have signed the CLA.

[samuelsadok]

This looks generally good, see one comment.
I also added a basic CI compile test, so when you push again it will pick up the new test and might require additional changes.

I'm a bit surprised that the STM32 Arduino core doesn't already come with a standard HardwareCAN implementation. Is pazi88/STM32_CAN.git the go-to CAN library that people use on STM32 Arduinos?

[samuelsadok]

The top three bits of id are reserved, with the MSB meaning "extended". Additionally, if data is null, it should send a remote request frame if the CAN lib supports it.

Suggested change

	msg.id = id;
	msg.id = id & 0x1ffffff;
	msg.flags.extended = id & 0x80000000;
	msg.flags.remote = data;

(not tested)

[BrechtSerckx]

I'm a bit surprised that the STM32 Arduino core doesn't already come with a standard HardwareCAN implementation. Is pazi88/STM32_CAN.git the go-to CAN library that people use on STM32 Arduinos?

There is no CAN support in STM32duino, see this issue: stm32duino/Arduino_Core_STM32#259. From the thread it seems like pazi88/STM32_CAN is a decent implementation that works on most STM32 devies.

[samuelsadok]

Ah yes I got the polarity flipped in my suggestion. msg.flags.remote = !data; would also have worked.

[samuelsadok]

Thanks for adding this!