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

Pavel Hofman pavel.hofman at insite.cz
Thu Mar 13 13:49:20 CET 2008

Takashi Iwai napsal(a):
> 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.

Well, I would not want to skip the check for cards with functioning rate 
detection. Plus snd_ak4114_check_rate_and_errors gets called 
periodically afterwards.

It would be great if the driver in slaved-clock mode cut its list of 
native sample rates to the only one currently fed to SPDIF input and 
detected by AK4114. A routine doing this would be called when switching 
clock to the slaved-clock mode and called again in 
snd_ak4114_check_rate_and_errors() when any change in input rate is 
detected (and the stream is not running). Going back to master-clock 
mode would restore the existing list of all the rates.

In case of input sample rate change when the PCM stream is running, the 
stream would be stopped. This is already implemented in the current 
version of snd_ak4114_check_rate_and_errors()

Unfortunately, I do not know how to change the rates list properly not 
to break something. If it is only about changing the HW params struct, 
that would be trivial.

Thanks for suggestions,


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