[alsa-devel] Buffer size for ALSA USB PCM audio

Alan Stern stern at rowland.harvard.edu
Thu Aug 29 17:00:57 CEST 2013

On Thu, 29 Aug 2013, James Stone wrote:

> On Wed, Aug 28, 2013 at 7:46 PM, Alan Stern <stern at rowland.harvard.edu> wrote:
> > On Wed, 28 Aug 2013, Clemens Ladisch wrote:
> >
> >> Sorry, what I said applies more to explicit sync endpoints.  When using
> >> implicit sync, a playback URB is submitted for each completed capture
> >> URB, with the number of samples per packet identical to the
> >> corresponding capture packet, so the parameters must be identical.
> >
> > Got it.  Below is an updated patch.
> >
> > James, the problem you encountered was most likely a result of the
> > faulty treatment of capture endpoints that Clemens pointed out.  It was
> > quite obvious in the usbmon traces that the unpatched driver used 8
> > packets per URB whereas the patched driver used 22.  This updated patch
> > should fix that problem.
> >
> Works fine. With this, it is possible to get clear playback at 64
> frames/period too. With vanilla 3.10.9, there was some glitchy
> distortion to the sound at that latency, so this seems to be an
> improvement.

That's good.  What happens if you push frames/period even lower?

Daniel and Eldad, more testing of the most recent proposed patch would
be welcome.

Alan Stern

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