[alsa-devel] Reg: Implementation of GSM digital audio path

Peter Ujfalusi peter.ujfalusi at nokia.com
Thu Jun 25 13:32:48 CEST 2009

On Thursday 25 June 2009 14:11:04 ext shariff wrote:
> Hi Peter,
>       Thanks for quick response. I understood some what from your mail.
>       I will explain, how my hardware is connected.
>                         USB GSM chip -> McBSP3
>                                                     McBSP2 -> TWL4030
>       Here, playback functionality will not be there in the GSM path. I
> need to take audio data from GSM. and redirect this to TWL4030 codec.

I see. Sorry I have confused things a bit,
In this case you need to do what Mark has suggested:
dummy dai for the codec, connect it to McBSP3 as it were a normal codec.
Than you will have two PCM on the sound card:
0.0: TWL digital audio
0.1: Your codec

arecord -Dplughw:0.1 | aplay -Dplughw:0.0
arecord -Dhw:0.1 | aplay -Dhw:0.0

>       The thing is, How and where to implement this GSM path without
> playback? as I am new to this ASoC framework.
>       What I understood from ur mail is.  Audio is being redirected from
> the application space i.e arecord will record and store in buffer and this
> buffer is
>       being played using aplay to other hardware (twl4030).
>       Can we handle the same thing in kernel space ( i.e in driver itself).

You anyway have to copy from one buffer to another to be in the safe side (in 
theory you could use the same buffer for recording and playback, but it should 
be avoided).
So you have to copy the samples from the capture buffer to the playback 
buffer. It really does not matter if it is done inside of the kernel or in 
user space.
This kind of 'routing' clearly belongs to the user space.

> Regards,
> Shariff


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