[alsa-devel] ASoC: Sharing Codec on SSC TDM

Fox, Jason P. JFox at gai-tronics.com
Wed Jun 22 22:36:38 CEST 2011

I have an application where I need an AD193X codec to be shared between
8 audio streams using one SSC channel on an AT91SAM9263. The AD1938
codec as configured in my driver has 8 channels. I need to be able to
send audio to the codec from 8 different tasks simultaneously. Each task
is to use only one channel.


We have the 8 TDM channels working in the driver. The first task can
access the codec and play audio just fine.  The second task cannot open
the device and gets an EBUSY return from snd_pcm_hw_open() because the
card is now owned by the first task.


However, the first task is only using one of the 8 channels.  I want the
second task to use the second channel, and so on.  


I can create an asound.conf that gives access to any one of the 8
channels, but only to one task at a time.  I've tried using dshare and
dmix, but that swamps the AT91 and there are lots of audio dropouts.
There is no need to mix audio between any of the streams, i.e. they are
all to be discrete audio outputs. 


What I am looking for is a way to structure the ASOC interface to allow
use of all 8 channels simultaneously.  If anyone can point me in a
direction, recommend a solution, or tell me where else to look it would
be VERY much appreciated.


Thank you for any help,

Jason Fox



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