[alsa-devel] [PATCH] ALSA: USB: adjust for changed 3.8 USB API

Eldad Zack eldad at fogrefinery.com
Sat Apr 27 15:08:51 CEST 2013

On Sat, 27 Apr 2013, Clemens Ladisch wrote:

> The recent changes in the USB API ("implement new semantics for
> URB_ISO_ASAP") made the former meaning of the URB_ISO_ASAP flag the
> default, and changed this flag to mean that URBs can be delayed.
> This is not the behaviour wanted by any of the audio drivers because
> it leads to discontinuous playback with very small period sizes.
> Therefore, our URBs need to be submitted without this flag.
> Reported-by: Joe Rayhawk <jrayhawk at fairlystable.org>
> Cc: <stable at vger.kernel.org> # 3.8 only
> Signed-off-by: Clemens Ladisch <clemens at ladisch.de>

This is slightly offtopic but related:

I figured a change of these semantics might impact consistent latency,
so I went ahead and tested this. It turns out that with my device
(uses implicit feedback) on current mainline I get up to +/- 10 frames 
change across stream restarts, while with 3.7.0 I get +/- 1 frame 
I restarted the stream about 20 times with each kernel.

So I tested this patch to see if it helps, but there's no change for my 
setup with 3.9.


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