Alsa & sound states

Al Johnson openmoko at
Fri Dec 12 11:42:20 CET 2008

On Friday 12 December 2008, Sargun Dhillon wrote:
> This is a multipart question about the Openmoko Freerunner. I
> basically want to know about the sound states the device can support,
> and currently supports.
> The ones which I'm wondering if it can support:
> 1) GSM out  -- > CPU in
> 2) GSM in   < -- CPU out
> 3) GSM out ---> CPU  ---> handset speaker
> 4) Handset Speaker ---> CPU --> GSM in
> 5) GSM --> CPU + handset speaker
> 6) Handset speaker + CPU ---> GSM
> How exactly do the audio states in alsa mixer map to the device? How
> many different inputs does the CPU have?
> Is call recording possible?
> Could these states be created?

See the block diagram in the wiki, and the wolfson datasheet linked from that 

From a quick look all your scenarios seem possible. I assume you mean to use 
the handset mic as a source in 4 and 6, not the handset speaker.

The CPU has a stereo input and a stereo output so, while you can treat the 
left and right as separate audio streams, the sampling will be linked. 
Depending on exactly what you want to do with the CPU this may or may not be 
a problem.

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