[alsa-devel] AK4114 - capturing spdif input stops the stream

[Takashi Iwai]

At Wed, 12 Mar 2008 23:50:08 +0100,
Pavel Hofman wrote:
> 
> Hi,
> 
> here is my scenario:
> 
> ICE1724 card, trying to record from SPDIF input via AK4114, ICE1724 
> slaved to SPDIF clock from the receiver.
> 
> The card detects SPDIF input rate correctly (in my case ESI Juli where 
> AK4114 is provided with independent clock signal to enable the rate 
> detection). Let's say it is 192000.
> 
> Now I want to arecord the input stream, let's say in CD quality, using 
> the plug plugin. The command fails, because of the check in ak4114.c:
> 
> res = external_rate(rcs1);
> 	if (!(flags & AK4114_CHECK_NO_RATE) && runtime && runtime->rate != res) {
> 		snd_pcm_stream_lock_irqsave(ak4114->capture_substream, _flags);
> 		if (snd_pcm_running(ak4114->capture_substream)) {
> 			printk(KERN_DEBUG "rate changed (%i <- %i)\n", runtime->rate, res);
> 			snd_pcm_stop(ak4114->capture_substream, SNDRV_PCM_STATE_DRAINING);
> 			res = 1;
> 		}
> 		snd_pcm_stream_unlock_irqrestore(ak4114->capture_substream, _flags);
> 	}
> 
> The stream gets stopped because res = 192000 and runtime->rate = 44100.
> 
> The problem is that the capture device still offers all the available 
> rates, instead of the single SPDIF input one. Thus, the plug plugin is 
> not forced to convert from 192000 to 44100 and runtime->rate is 44100 
> instead of 192000.
> 
> Of course recording at 192000 works fine.
> 
> What would be the best way to force the SPDIF capture device to offer 
> (advertise) only the current rate? This functionality would have to be 
> applicable only to the few cards correctly detecting incoming rate 
> (unlike most ice1724 cards without independent clock in slave mode).

What about to call snd_ak4114_check_rate_and_errors() at PCM open?
You can pass AK4114_CHECK_NO_RATE to flags argument to skip the check
there, at least.


Takashi