[alsa-devel] Sample rates above 192000

[Mike Looijmans]

Found the cause: snd_pcm_limit_hw_rates()

soc-code.c:soc_pcm_open() calculates the min/max rates for the given 
link, then passes the result to snd_pcm_limit_hw_rates which discards 
this and replaces it with incorrect data derived from the PCM flags.

The 3.8 kernel soc-core looks totally different, so I have no clue if 
this still applies.

If a codec defines rate_min=16000, rate_max=96000 and the DAI specifies 
flags for 8000..192000 Hz, then the resulting limits that it will apply 
are rate_min=8000 rate_max=192000. One would expect the more restrictive 
values to prevail. Similar, if both codec and dai specify 
rate_max=216000 then the resulting rate_max will surprisingly be set to 
192000.

I worked around the issue by simply adding a 204800 rate to the table of 
known rates.

Mike.


On 04/17/2013 10:21 AM, Mike Looijmans wrote:
> I'm trying to use "my" hardware at a 204800 sample rate. I've changed
> the DAI and codec limits to match. If I limit them to anything below
> 192kHz, everything behaves as expected and I can record at up to that
> rate, also if that rate is not a multiple of 48k or 44k1 (using
> "SNDRV_PCM_RATE_KNOT" constant).
>
> When I specifiy anything over 192000, I bump onto some ceiling, and I
> cannot figure out what's causing it. I patched alsa-utils to allow
>  >192000 already (there is a silly check on that in aplay.c which bails
> out early without asking the driver).
>
> # arecord -D hw:ADC8 --duration=5 -f S32_LE -c 2 -r 204800
> /tmp/recording.wav
> Recording WAVE '/tmp/recording.wav' : Signed 32 bit Little Endian, Rate
> 204800 Hz, Stereo
> Warning: rate is not accurate (requested = 204800Hz, got = 192000Hz)
>           please, try the plug plugin
> #
> # arecord -D hw:ADC8 --duration=5 -f S32_LE -c 2 -r 192000
> /tmp/recording.wav
> Recording WAVE '/tmp/recording.wav' : Signed 32 bit Little Endian, Rate
> 192000 Hz, Stereo
> #
>
>
> I also tried a "grep" on the kernel (i'm still on 2.3.7 though) source
> files on "192000" but found nothing that would limit the sample rate to
> that. I'm running out of ideas. How can I break this limit? Or where in
> the kernel can I find the part that calculates the max rate?
>
> Mike.