From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: Fixed sampling freq UAC2 doubt Date: Mon, 24 Jan 2011 14:21:59 +0100 Message-ID: References: Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.suse.de (cantor.suse.de [195.135.220.2]) by alsa0.perex.cz (Postfix) with ESMTP id EA5B21038B0 for ; Mon, 24 Jan 2011 14:21:59 +0100 (CET) In-Reply-To: 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: Jassi Brar Cc: alsa-devel@alsa-project.org, Clemens Ladisch , Daniel Mack List-Id: alsa-devel@alsa-project.org Added relevant guys to Cc.... At Fri, 21 Jan 2011 17:35:52 +0900, Jassi Brar wrote: > > 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. >