[alsa-devel] About the buffer_time and period_time

[Liam Girdwood]

On Tue, 2007-10-16 at 16:27 +0800, Fengwei Yin wrote:
> Hi all,
> I met a problem about period_time/buffer_time on PXA with ASOC enabled.
> The kernel version is 2.6.21.
> 
> The Audio stream is 32k which is not supported by PXA ASOC driver. Please
> refer following
> RATES definition for PXA2xx.
> 
> #define PXA2XX_AC97_RATES (SNDRV_PCM_RATE_8000 | SNDRV_PCM_RATE_11025 |\
>                 SNDRV_PCM_RATE_16000 | SNDRV_PCM_RATE_22050 |
> SNDRV_PCM_RATE_44100 | \
>                 SNDRV_PCM_RATE_48000)
> 

This may be a bug in the pxa AC97 driver as most AC97 codecs can run at
32k and hence drive the AC97 link at 32k. I assume your using the WM9713
and this will request from the pxa AC97 controller when it needs PCM
audio data in VRA mode. i.e. it will mark every 2 out of 3 AC97 frames
(slot 3 & 4) as valid.

Can you set SNDRV_PCM_RATE_32000 and give it a try, hopefully it should
work and wont require any sample rate conversion.

Liam