arduino
CAN.write() return-code does not comply to API spec
CAN.write() in this core returns 0 for errors but should return a negative error code.
Details
The docstring for the Arduino CAN API states that HardwareCAN::write() returns:
1 if the message was enqueued, an implementation defined error code < 0 if there was an error
This core implements HardwareCAN::write() by calling mbed::CAN::write() and directly returning the result (code, header).
However mbed::CAN::write() has a different spec for returning errors:
0 if write failed, 1 if write was successful
Discussion
This was brought up by @bthacher-crabi in https://github.com/odriverobotics/ODriveArduino/issues/4 and I'd be interested what the maintainers of this repo think. Technically the meaning of return 0 is unspecified in the API, so it's unclear what client code should do with it. It's conceivable that other cores use 0 to mean "success" (which is a fairly common convention). Should we add a preprocessor special case for the mbed core specifically?
Separately, going forward it would be cool if either the code or the API specs are changed so that they are consistent.
