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SubjectRe: Handshaking on USB serial devices
> To make it clear: Even aside from the buffer in 2.6's pl2303.c, there's
> a race: An in-flight write URB can fill all hardware buffers, making
> unsafe what previously appeared to be a safe write. I think it's
> essential to delay submission of the URB on a stop-transmit condition.

Hardware flow control *is* a race, and always will be. The remote end has
a delay in signalling 'stop' there is a propogation delay and a response
delay. This is why most implementations assert stop a bit *before* they
run out.

Given the size of transfers and the internal buffering one would hope the
USB devices do their own flow control if told to properly.

Alan


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