From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jassi Brar Subject: Fixed sampling freq UAC2 doubt Date: Fri, 21 Jan 2011 17:35:52 +0900 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-bw0-f51.google.com (mail-bw0-f51.google.com [209.85.214.51]) by alsa0.perex.cz (Postfix) with ESMTP id 4A3392458E for ; Fri, 21 Jan 2011 09:35:53 +0100 (CET) Received: by bwz10 with SMTP id 10so1324863bwz.38 for ; Fri, 21 Jan 2011 00:35:52 -0800 (PST) List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: alsa-devel@alsa-project.org Cc: Takashi Iwai List-Id: alsa-devel@alsa-project.org Hi, While testing my under-development generic USB Audio Class 2.0 _gadget_ driver with ALSA's USB Audio Class driver, I came across an apparent discrepency. Or so do I think. Page-98 Section 5.2.5.1.1 of 'Audio 20 final.pdf' specifies :- [In many cases, the Clock Source Entity represents a crystal oscillator based generator with a single fixed frequency. In that case, the Set request is not supported.] Here 'not supported' means setup requests for CUR/RANGE CS_SAM_FREQ_CONTROL should stall. Right ? The snd_usb_hw_params in sound/usb/pcm.c apparently attempts to do that with disregard to Clock-Frequency-Control bitmask in bmControls field of the Clock Source Descriptor. The confusion is, subs->cur_rate is initialized only if snd_usb_init_sample_rate succeeds. Which does SET control tranfer, albeit with the supported frequency. Couldn't a fixed sampling freq UAC2 compliant device refuse to work in that case, thereby failing any attempt to use the USB card? Could someone please point where I got it wrong and/or if such a card works with ALSA USB? Thanks.