From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Henningsson Subject: Re: Delay calculations for USB audio? Date: Fri, 28 Sep 2012 19:29:09 +0200 Message-ID: <5065DE65.5090004@canonical.com> References: <5065834E.4010707@canonical.com> <506588A2.4070602@gmail.com> <5065907C.8030904@canonical.com> <5065987A.1080703@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from youngberry.canonical.com (youngberry.canonical.com [91.189.89.112]) by alsa0.perex.cz (Postfix) with ESMTP id 0E12C2615EA for ; Fri, 28 Sep 2012 19:29:10 +0200 (CEST) In-Reply-To: <5065987A.1080703@ladisch.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Clemens Ladisch Cc: alsa-devel@alsa-project.org, "Gabriel M. Beddingfield" List-Id: alsa-devel@alsa-project.org 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. https://launchpad.net/~diwic