[alsa-devel] [PATCH 1/3 v1] ALSA: usb-audio: more tolerant packetsize

[Jiada Wang]

Hello Clemens

On 12/01/2016 04:15 AM, Clemens Ladisch wrote:
> Jiada Wang wrote:
>> On 11/30/2016 11:41 PM, Clemens Ladisch wrote:
>>> Jiada Wang wrote:
>>>> since commit 57e6dae1087bbaa6b33d3dd8a8e90b63888939a3 the expected packetsize is always limited to
>>>> nominal + 25%. It was discovered, that some devices
>>> Which devices?
>> It was a LG nexus
> So it was the Android audio accessory mode.
>
>>>> have a much higher jitter in used packetsizes than 25%
>>> How high?
>> the nominal packet size was somewhere around 176bytes
>> +25% would result in max expected packets to be ~220bytes
>> We observed some packets exceeding this size (256byte)
> 256 bytes per USB frame would correspond to 64 kHz, instead of the
> nominal 44.1 kHz.
>
> The audio accessory sample format is fixed, and that mode is no longer
> developed, so increasing the limit to +50% would be sufficient to work
> around this problem.
>
> I don't know if this is a bug in Google's generic AOA code, or if LG did
> some changes; I have not heard any other report so far ...
>
We also reproduced the same issue with following android devices,
* Samsung S4, Android 4.2.2, model GT-I9505
* Sony Xperia Z, Android 4.2.2, model number CC6603
* LGE Nexus 4, Android 4.2.2
so it most likely not a LG specific issue.

I agree to increase to +50% would be sufficient to avoid this issue.

Thanks,
Jiada


> Regards,
> Clemens