[alsa-devel] Asynchronous audio USB chips: choppy playback since 3.8-rc7

[Michael Trimarchi]

Hi Daniel

On 03/04/13 15:55, Michael Trimarchi wrote:
> Hi Daniel
> 
> 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 
>>> regression.
>>>
>>> The bug is described in detail here:
>>>
>>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1136110?comments=all
>>>
>>> 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.

Sorry the comment was for a bug that is not included in this list and recently fixed.
USB: EHCI: fix bug in iTD/siTD DMA pool allocation

Michael

> 
> http://www.m2tech.biz/hiface_dac.html
> 
> Michael
> 
> 
>>
>> 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?
>>
>>
>> Thanks,
>> Daniel
>>
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>