[alsa-devel] Questions about alsa driver for i.Mx27 + wm8974: playback time shorter than the original record time

Jie Jiang jjinfo at nudt.edu.cn
Tue Aug 31 18:21:40 CEST 2010

Hi Mark,

Thanks for your advice!

On Thu, 2010-08-26 at 13:41 +0100, Mark Brown wrote:
> On Thu, Aug 26, 2010 at 08:05:38PM +0800, Jie Jiang wrote:
> > The configuration of mx27 ssi1 transmission channel is as follows(using
> > ssi api from kernel
> This is an extremely old kernel version, the current kernel version is
> 2.6.35 with 2.6.36 in development.  Current mainline kernels have a
> different API for configuring the IOMUX.  I'd strongly recommend working
> with a more current kernel if you're looking for community support.
> > Here I'm not very sure about the setting of frame rate and frame sync
> > length.  Is the above setting right?  But even I set frame rate to 1, it
> > does not make any difference. 
> > What's the possible reason causing the incorrect faster playback speed?
> > Any suggestion is appreciated.
> Normally this will be the result of either an incorrect frame rate or
> the hardware trying to play back mono data as stereo (which will cause
> data to be consumed as twice the expected rate).

Yes, it seems to be this reason that causes problem.
When I playback a stereo wav file(8kHz,16bit, stereo), everything goes
well.But when trying to playback a mono wav (8kHz,16bit, mono)file,
problem stills exist.

What's the possible reason for incorrect handling of mono file?
How to solve it so I can playback mono file correctly?


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