[alsa-devel] Delay calculations for USB audio?

Clemens Ladisch clemens at ladisch.de
Fri Sep 28 14:30:50 CEST 2012

David Henningsson wrote:
> On 09/28/2012 01:23 PM, Gabriel M. Beddingfield wrote:
>> On 09/28/2012 06:00 AM, David Henningsson wrote:
>>>   * Selecting the outer USB port instead of the inner one. Yes, there
>>> are two USB ports next to each other, and this only happens on one of
>>> them. (!))
>> The last statement sounds like you're sharing a hub with another device
>> that has reserved bandwidth.  For example, a USB webcam will often do
>> this.  Audio will work for a while and then get pre-empted.

For A/V devices, USB bandwidth is reserved in advance; it is not possible
to have other device interfere (as long as the controller driver is
written correctly ...).

> Thanks! Indeed, when deactivating bluetooth (in both kernel 3.2 and 3.5)
> the sound is back to normal

I'd guess that that particular USB port and the bluetooth controller
share an interrupt.

> is it actually fixable if we wrote better drivers?

Apparently, yes.


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