[alsa-devel] soc-dsp questions

[Liam Girdwood]

On 11/06/11 12:48, Mark Brown wrote:
> On Fri, Jun 10, 2011 at 06:19:57PM -0700, Patrick Lai wrote:

> 
>> Another query I have is how to handle back-end error. The audio bus
>> which is running on my machine requires close coordination between CPU
>> and CODEC. Essentially, if one side is unable to respond to incoming
>> data in time, data exchange halts. I am looking for way to reset both
>> CPU and CODEC back to fresh state. One approach I am thinking is to
>> generate XRUN error(snd_pcm_stop(SNDRV_PCM_STATE_XRUN) and have
>> application call prepare() to reset CPU and CODEC back to good state.
>> I see each back-end is registered as PCM device so it's possible that
>> application can read /dev/snd/timer to get notified. However, do I call
>> prepare() on one of FE PCM devices that are routed to the back end in
>> question? Would this approach work? Any suggestion?
> 
> I'd expect that from an application point of view this will just work
> already?  The application will just operate on the PCM it's operating on
> and will notice a stall in the same way it does for any other device
> then the front/back end machinery will connect everything up in the same
> way it does for every operation when (if!) the application tries to
> recover.

This is how it works on OMAP4. 

The ABE handles and recovers most BE errors internally and can also interrupt the CPU for serious errors (to signal XRUNs etc).

Liam