Provide very bare-bones minimal success/error codes for CAN API.

[aentinger]

This is related to arduino/ArduinoCore-mbed#956 as well as to arduino/ArduinoCore-mbed#924 .

The underlying problem is that different HALs provide different errors and different error codes when it comes to any peripheral usage (though we concern ourselves with CAN in this PR).

I propose to add at least those two very generic error codes at this very moment with the aim to expand error codes (i.e. CAN_TX_FIFO_FULL) further in the future.

[aentinger]

Thoughts @facchinm ?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.53%. Comparing base (4a02bfc) to head (6c411fe).

Additional details and impacted files

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##           master     #237   +/-   ##
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  Coverage   95.53%   95.53%           
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  Files          16       16           
  Lines        1075     1075           
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  Hits         1027     1027           
  Misses         48       48           

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[facchinm]

Definitely agree on the concept. On the numbering, it really depends on the expected pattern to consume these values. Eg:
while (!can.write()) could mean "keep trying until the error disappears", so CAN_ERROR_GENERIC should be 0 (which is also consistent with the Print.write API (returns the number of bytes actually written, so 0 bytes in case of error).

[facchinm]

See comment in thread

[aentinger]

Ciao @facchinm ☕ 👋

That's allright with me. It is a little bit at odds with the current error definition but I'd say we have a chance right now to create a clean API. What do you think (concerning possible API breakage)?

[facchinm]

What about adopting Print strategy and add setWriteError/getWriteError while returning 0 on failure?