On Tue, 2 Jul 2013, Clemens Ladisch wrote: > Alan Stern wrote: > > 256 samples/period / (44100 samples/second) * 8000 microframes/second > > = 46.44 microframes/period. > > > > Therefore I would expect to see snd-usb-audio submitting isochronous > > URBs with 46 or 47 packets, with a pipeline depth of 2 URBs. > > > > However, that's not what actually happens. The audio-out stream uses 8 > > URBs each containing about 7 packets on average, for a latency of 7 ms. > > The audio-in stream uses 8 URBs each containing 1 packet, for a latency > > of 0.125 ms and a pipeline duration of 1 ms -- which is too small for > > the current version of ehci-hcd to accept. > > IIRC 8 x 1 frames worked once upon a time. And it will once again, after the conversion to tasklets. :-) > Anyway, the driver attempts to keep a minimum size of 1 ms for each URB, > but also uses wMaxPacketSize to compute this and assumes that this is > not too far off from the actual packet size. This appears to be the > first device to use a ridiculously large value of 1024 bytes. I thought this might be related to the problem. It was quite noticeable in the usbmon trace that the input data occupied only 40 or 48 bytes of a 1024-byte buffer. > I'll fix this in the driver. Thank you. Alan Stern -- 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
