From: Takashi Iwai <tiwai@suse.de>
To: Jassi Brar <jassisinghbrar@gmail.com>
Cc: alsa-devel@alsa-project.org, Clemens Ladisch <clemens@ladisch.de>,
Daniel Mack <daniel@caiaq.de>
Subject: Re: Fixed sampling freq UAC2 doubt
Date: Mon, 24 Jan 2011 14:21:59 +0100 [thread overview]
Message-ID: <s5h62te8miw.wl%tiwai@suse.de> (raw)
In-Reply-To: <AANLkTinCZyrS6GDKfs3WerNrQ7DaF6_nMHLCaWqERmxC@mail.gmail.com>
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.
>
next prev parent reply other threads:[~2011-01-24 13:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-21 8:35 Fixed sampling freq UAC2 doubt Jassi Brar
2011-01-24 13:21 ` Takashi Iwai [this message]
2011-01-27 8:14 ` Clemens Ladisch
2011-01-29 11:29 ` Jassi Brar
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