Mailbox checking

[anfroholic]

Edge_Boards/poc/ocan.py

Line 74 in 1ecdb35

while r is None:

Having played with this there's a lot of time waiting for the timeout and handling the exception. And while I don't think we want code like this in general it seems like checking the mailbox first and then attempting to receive is better.

Something more like:

while True:
    if(can.any(0)):
        break
can.receive(0)

again, I don't believe we want blocking code like this and moreover we want to use the can.rxcallback() function so we can see if we've missed any messages. At which point we would throw a fault or something, I've got an idea on how this could be handled but it's for a future discussion