d2c05e201f
one specific problem: the driver didn't check for ACK/NAK after writing a slave address byte to the bus, and some slaves signal that they are busy (such as when completing an internal write to flash memory) by sending a NAK in response to being addressed. While working on that problem I discovered that the driver's handling of error conditions in general didn't match the state transition diagram in the reference manual, and making that right resulted in a lot of code reorganization. Along the way various other changes also happened... - Remove a mutex that wasn't protecting anything. - Remove some mystery DELAY()s, document the few that remain. - Use pause_sbt(9) to yield the processor for the bulk of the time it takes to transfer each byte rather than busy-polling the whole time. - Disable the controller when no transfers are in progress; since we don't operate in slave mode, there's no reason to run the hardware. - Remove a bunch of unecessary code from probe().
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