[alsa-devel] USB Audio questions

David Henningsson david.henningsson at canonical.com
Tue Aug 16 07:30:53 CEST 2011

On 08/15/2011 10:31 PM, Pierre-Louis Bossart wrote:
> - Increasing the number of packets/urbs solves my power issue but not the
> synchronization issue. If I reduce the number of urbs to reduce the
> interrupt rate, then the accuracy of the hw_pointer is decreased big time
> and it becomes difficult to synchronize with video.

I think the same thing is a problem for quite a few other devices as 
well - I wonder if we need some kind of "pointer granularity" variable 
to be exported through the ALSA API? PulseAudio could use that to 
determine whether or not to enable timer-based scheduling. And in these 
cases, maybe a call to hw_pointer could return hw_pointer and time, and 
then PulseAudio etc could use that for extrapolation (or the 
extrapolation could be done in alsa-lib).

David Henningsson, Canonical Ltd.

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