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

Pavel Hofman pavel.hofman at insite.cz
Thu Mar 13 20:18:34 CET 2008

Takashi Iwai wrote:
> At Thu, 13 Mar 2008 13:49:20 +0100,
> Pavel Hofman wrote:
>> 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.
> Yes, but the check there is simply useless at open.  It's only for
> running states.  snd_ak4114_external_rate() would be simler, then.
>> 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.
> Suppose that the slave <-> master mode change doesn't happen during
> the stream is opened, it's relatively easy.  So far, ice1724.c doesn't
> call spdif.ops.open/close callbacks.  Call them in *_spdif_open/close
> functions with NULL check. Then add open hook in juli.c so that you
> can change rates_min and rates_max to the currently detected rate at
> open...
> Well, it's faster to write a patch than texts.


Takashi, thanks for the patch, it works flawlessly.

Another issue - when the external clock changes rate and the stream is 
running (typically when starting the source playback which switches the 
source card (and its SPDIF-OUT) to a different frequency), the target 
card detects the change and the capture stream is stopped in 
snd_ak4114_check_rate_and_errors() by

snd_pcm_stop(ak4114->capture_substream, SNDRV_PCM_STATE_DRAINING);

How should recording applications behave with stream in this mode? I 
would expect arecord to close, but it does nothing. Is this correct 



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