[alsa-devel] Delay calculations for USB audio?

David Henningsson david.henningsson at canonical.com
Fri Sep 28 19:29:09 CEST 2012

On 09/28/2012 02:30 PM, Clemens Ladisch wrote:
> 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.

In this case, actually the bluetooth controller is on the same USB bus, 
so that's why they're sharing the interrupt. And when I click the rfkill 
button, it disappears from the bus, just as if it were an external 
bluetooth adapter that I unplugged.

>> is it actually fixable if we wrote better drivers?
> Apparently, yes.

Okay, so if I get some time to dig deeper into this, where should I 
start looking? Maybe in the bluetooth controller driver, if that's 
what's interfering?

David Henningsson, Canonical Ltd.

More information about the Alsa-devel mailing list