[alsa-devel] Asynchronous audio USB chips: choppy playback since 3.8-rc7
michael at amarulasolutions.com
Wed Apr 3 15:55:49 CEST 2013
On 03/04/13 12:23, Daniel Mack wrote:
> Hi David,
> On 03.04.2013 12:15, David Henningsson wrote:
>> Just to get your attention here on what seems to be an USB audio
>> The bug is described in detail here:
>> Quoting the bug:
>> This bug seems to affect only a certain kind of hardware, which is
>> called "Asynchronous USB Digital Audio Codec (DAC)". It's said that such
>> a DAC hosts the clock itself (USB Device Host). An ordinary DAC, so
>> called "Synchronous USB DAC", uses the clock hosted by the mother board,
>> which is not affected by this bug.
>> When this bug affects an asynchronous USB DAC, the audio played by the
>> DAC is constantly interrupted. The playback itself does not stop, but
>> the output becomes discontinous, filling with constant crackling noises,
>> destroying everything the DAC plays.
>> According to the bug reporter, which seems to have done quite a bit of
>> research, this started between 3.8-rc6 and 3.8-rc7 as well as stable
>> kernels and the bug also lists a few commits which could be the cause,
>> none under sound/usb though.
> There were no relevant changes for snd-usb between the two versions
> mentioned. The only patches that come in mind in this time window are:
> 3e619d041 "USB: EHCI: fix bug in scheduling periodic split transfers"
> b09a61cc0 "USB: EHCI: fix for leaking isochronous data"
This last one, doesn't give me any problem, just a memory leak and not a choppy
playback (tested on 48Khz, 96Khz, 192Khz 32bit on OMAP3 device) and I don't
think that it can be the reason of the problem.
> And they have both been back-ported to stable. Copied Alan for reference.
> Any chance some of the bug reporters could try and revert exactly those
> for testing?
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