From mboxrd@z Thu Jan 1 00:00:00 1970 From: Damien Zammit Subject: - snd-usb-audio - SPDIF clock source mixer control for Digidesign Mbox Date: Wed, 29 Oct 2014 21:21:29 +1100 Message-ID: <5450BFA9.1090908@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by alsa0.perex.cz (Postfix) with ESMTP id 743A12604C9 for ; Wed, 29 Oct 2014 11:21:34 +0100 (CET) Received: by mail-pd0-f175.google.com with SMTP id y13so2697411pdi.6 for ; Wed, 29 Oct 2014 03:21:33 -0700 (PDT) Received: from [192.168.140.2] (14-201-185-176.static.tpgi.com.au. [14.201.185.176]) by mx.google.com with ESMTPSA id fy4sm3941752pbb.42.2014.10.29.03.21.31 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 29 Oct 2014 03:21:32 -0700 (PDT) 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 Hi all, As some of you may remember, the Digidesign Mbox has a multiple endpoint interface and does not follow the standard USB audio spec. I am pretty sure that the first interface 0 is for firmware upgrades only, and the second interface has 2 endpoints one for playback and one for capture. I have heard that the SPDIF output is always on, but there is a special command to change the clock source to external sync with SPDIF. I think I have found the correct USB command for changing the clock source of the device to SPDIF external sync. I tried to use a pair of the devices in JACK using a pcm_multi configuration and syncing one of them to the other with a RCA cable, but unfortunately I get lots of XRUNs in JACK and I am wondering if there is a reason for this? Can someone who knows about the pcm_multi stuff shed some light on why I might be getting thousands of XRUNs when I use two identical USB soundcards that are (hopefully) synced to each other? I have written a non-standard mixer control for this so alsamixer can select the external clock source. Basically, the command to set SPDIF sync seems to include a sample rate command, but the sample rate is set to zero for SPDIF sync. Could JACK be resetting the sample rate and overriding my command perhaps? How would I override the ALSA driver code so that the sample rate is not reset by JACK to 48000 instead of 0 but only when the mixer control sets the flag? Damien