From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Keith A. Milner" Subject: Re: Attempting to understand odd snd-usb-audio code and behavior Date: Wed, 23 Aug 2017 23:49:51 +0100 Message-ID: <4630623.QtToMlzcyD@kamdesktop> References: <2006820.TBXnYHJvYE@kamdesktop> <1954362.aJMGcWAYHc@kamdesktop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wm0-f44.google.com (mail-wm0-f44.google.com [74.125.82.44]) by alsa0.perex.cz (Postfix) with ESMTP id 2189826780D for ; Thu, 24 Aug 2017 00:49:54 +0200 (CEST) Received: by mail-wm0-f44.google.com with SMTP id l19so8687485wmi.1 for ; Wed, 23 Aug 2017 15:49:54 -0700 (PDT) Received: from kamdesktop.localnet (e.5.5.f.4.0.b.1.0.d.6.9.3.d.9.8.d.a.9.2.a.0.e.b.0.b.8.0.1.0.0.2.ip6.arpa. [2001:8b0:be0a:29ad:89d3:96d0:1b04:f55e]) by smtp.gmail.com with ESMTPSA id x4sm1862641wrd.66.2017.08.23.15.49.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Aug 2017 15:49:52 -0700 (PDT) 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: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org On Wednesday 23 Aug 2017 14:52:43 Clemens Ladisch wrote: > Keith A. Milner wrote: > >>> kernel: [ 1987.452947] usb 1-1: Unable to change format on ep #8e: > >>> already in use> > > So the error messages are due to a userspace app trying to open playback > > and capture at the same time? > > For this device, playback requires a running capture stream to determine > the rate of packets. Interestingly, the device works for playback (using aplay) until I try to capture, when it stops working until I reset it. > This error happens when the application tries to > open the capture stream after the playback stream. (If the format does > not actually need to change, the error message is misleading.) > > Your actual problem is that the device does not send any capture packets. > Presumably this should (in principle) be taken care of by the driver. The application should not care. So the driver should detect the dependency and open the corresponding capture stream if a playback stream is opened? There's definitely something hooky with this device and the capture stream though, which I need to explore further. So far I cannot get capture working at all. Cheers, Keith