From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Mack Subject: Re: USB hardware that supports implicit feedback? Date: Sun, 18 Nov 2012 18:10:29 +0800 Message-ID: <50A8B415.5010008@gmail.com> References: <50A57933.9070607@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pa0-f51.google.com (mail-pa0-f51.google.com [209.85.220.51]) by alsa0.perex.cz (Postfix) with ESMTP id 5FC602615AA for ; Sun, 18 Nov 2012 11:11:41 +0100 (CET) Received: by mail-pa0-f51.google.com with SMTP id fb11so519424pad.38 for ; Sun, 18 Nov 2012 02:11:40 -0800 (PST) In-Reply-To: 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: Daniel Griscom Cc: Eldad Zack , Alsa Developer List-Id: alsa-devel@alsa-project.org On 16.11.2012 10:39, Daniel Griscom wrote: > At 7:22 AM +0800 11/16/12, Daniel Mack wrote: >> Hi Daniel, >> Hi Elad, >> >> On 16.11.2012 05:32, Daniel Griscom wrote: >>> At 10:02 PM +0100 11/15/12, Eldad Zack wrote: >>>> Hi Daniel, >>>> >>>> On Thu, 15 Nov 2012, Daniel Griscom wrote: >>>>> I'm having trouble getting implicit feedback working with my custom >>>>> capture/playback USB audio class device, even with the latest kernel. I >>>>> presume it's a problem with my device's configuration, but >>>>> can't figure out >>>>> exactly what the problem is (after a whole lotta investigation). >>>> >>>> What exactly doesn't work? >>> >>> The audio output stream (from the computer to my device) runs at a >>> few frames per second higher or lower rate than that of the input >>> stream (from my device to the computer). The actual difference seems >>> to be stable on a specific machine, but varies greatly between >>> machines (I've seen differences from +7fps to -2fps; I presume this >>> is due to differences in CPU clock frequencies). >> >> So you're saying that this is what you experience after you added code >> to make the driver use the implicit feedback mechanism? Over which time >> did you measure this and how exactly? Because frankly, I doubt that - >> the data rate is purely derived from the number of incoming samples. > > This has been the case for a while; we started work with ALSA 1.0.23, > but upgrading to kernel 3.6.6 (with included ALSA code) didn't change > anything. We have yet to do any patching of ALSA for this matter. Well, afaik, ALSA 1.0.23 is what ships with a kernel <= 3.4, and the code for implicit feedback went in for 3.5. >> Does your device demand the same number of *bytes* or samples/channel to >> be sent? > > I'll have to check that. Let me rephrase the question: does the number of input and output channels match? Eldad had a patch in his series that should make it work for both scenarios. >> The code I wrote for implicit feedback is used by the M-Audio FTU >> devices, > > So, with an FTU the implicit feedback code works? Yes, it does for many others. > What version of > kernel/ALSA should I use - the latest? Yes, always use the latests from git, especially for such relatively new features. Daniel