When UART timeout of zero is given, make read() return data already a…

[PaulKierstead]

…vailable

Currently if you give a timeout of zero to UART, typically you'll get nothing as the comparison is < timeout and no time has passed. This makes that <= and makes sure only one pass of the read loop is performed. Now, when a timeout of 0 is given, it will return the data already available without waiting for any additional data.

[ladyada]

@PaulKierstead thanks for the PR! one thing to check if you can - we want to make circuitpython a subset of CPython so code from circuitpython works on any os - for UART we want to mimic pyserial so can you see if this behavior is also specified there?

[PaulKierstead]

For read timeouts, pyserial behaviour for timeout == 0:
timeout = 0: non-blocking mode, return immediately in any case, returning zero or more, up to the requested number of bytes

So this would get us closer to pyserial (though of course many differences remain, but the others generally require CP to change its API in backwards compatibility broken ways).

[ladyada]

cool - thank you! that's good to hear, i'll wait for @tannewt or @dhalbert to review for possible mergin' - its a long weekend so may be a few days :)

[dhalbert]

Great! Thank you!

[PaulKierstead]

My pleasure, @ladyada and @dhalbert, I'm glad to contribute even this tiny change to a project that has provided many hours of fun and fulfillment.

[ladyada]

yay! nice work :)