[alsa-devel] Channel swapping issue on TI OMAP3/TWL4030

Peter Ujfalusi peter.ujfalusi at nokia.com
Tue Feb 15 07:59:50 CET 2011

On 02/14/11 19:58, ext ylin at mail.com wrote:
>> I have not experienced with channel swapping during capture..
>> It would help, if I know:
>> what is your kernel version
>> Source of the recording (digimic, HS, main mic, etc)
> We are using 2.6.32.  The source of the recording is using Analog Mic.  
> The Left Main mic is always on, and Right Sub mic can be either on or 
> off when this occurs.  We are not using AUX or digimic.
>> To clarify:
>> you experience sudden channel switch during active recording, when
>> the recording was running for few hours?
>> Or is it that you start/stop the recording, and sometimes the channels
>> are swapped?
> It is sudden channel switch during active recording.  There is no XRUN 
> or any noticeable error when this happens.
> This is a VoIP app, we have duplex audio when this happens.  Both 
> capture and playback are setup to run at 48kHz, 2 channel, S16_LE, with 
> period size 10 mSec.

I forgot to ask:
what mode you are using the McBSP?
Is it in element, or threshold mode?
You can check/change the McBSP mode in:

> For playing, the left and right are the same data, we could not tell if 
> the channel switch happens to playback as well.

I see. Is there a way for you to run your application to capture only,
and from a separate app (aplay?) play a sample, which has audio only on
one channel?


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