Alan Stern wrote: > The audio-out stream uses a pipeline of only 2 URBs. The URBs start > out alternating between 8 and 7 packets apiece. This yields a total > latency around 1.9 ms (equivalent to 2 periods of about 41 frames at > 44.1 KHz), which is smaller than I would expect (2 periods of 64 frames > works out to 2.9 ms). > > Anyway, this sort of works. Every so often (roughly at intervals of 15 > ms) there is an underrun. Evidently the computer's EHCI hardware > sometimes requires URBs to be submitted more than 7 microframes in > advance. It would be trivial to make the driver respect these constraints, if only there were some mechanism to know about them. > After a second of this, the URBs suddenly changed. They began to > alternate between 7 and 5 packets; one of them had only 4. I have no > idea why this happened. On this device, the host's playback rate is controlled by the device's frequency feedback. It's possible that all those underruns have confused the device's sample counter. Regards, Clemens -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
