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USB latency strangeness
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USB latency strangeness

Hi all,

I've run into problems with latency when sending and receiving messages to and from my USB device. The device is controlled via firmware commands which are sent over the bulk out pipe and whose responses are read in through the bulk in pipe.

Each firmware command takes 0.5 seconds with my driver, which is 3 orders of magnitude too slow. The corresponding Windows driver for the same device reports firmware command turnaround times of between 500 and 1200 _micro_seconds.

I've also noticed data transfer is too slow by a factor of 20 or so. My guess is that maybe something's working in low speed or full speed mode, instead of high speed. However, that wouldn't explain the terrible latency I'm experiencing. The amounts of data that I'm transmitting are so low (~20 bytes, on average), that data transfer time can't be the reason.

Any ideas?

Cheers,
Gerald
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