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

Daniel Mack zonque at gmail.com
Tue Aug 13 23:34:15 CEST 2013

Hi Alan,

On 13.08.2013 23:06, Alan Stern wrote:
> On Mon, 12 Aug 2013, Alan Stern wrote:
>> On Mon, 12 Aug 2013, Takashi Iwai wrote:
>>> So... Clemens, Daniel, Eldad, could you guys review the latest version
>>> of Alan's patch?  I'd love to sort this out for 3.12.
>> Here's a revised version of the patch (still untested).  The difference
>> is that this version tries always to keep a period's worth of bytes in
>> the USB hardware queue.  This will provide better protection against
>> underruns when the period is larger than the queue's minimum
>> requirement.
> After more thought, I decided that patch does too much.  It's not 
> necessary to keep track of the number of packets.  Instead, the driver 
> should always try to keep as much data in the USB hardware queue as it 
> is allowed to.
> In other words, there should be enough URBs so that an entire ALSA 
> buffer can be queued at any time, subject only to the limit on the 
> maximum number of URBs and packets.  It doesn't make sense to allocate 
> just enough URBs to cover a single period.
> Does this seem reasonable?

I think so, yes. But I'd like to comment on the actual patch, and also
give it a try first of course. It took me some days to gather my setup
again, but if you send a revised version, I hope to be able to test it
in the next days.


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