[alsa-devel] [ASoc] TDM over one SSC channel on AT91 possible?

Caleb Crome caleb at crome.org
Fri Jun 24 08:07:16 CEST 2011

Heh, this is kind of the opposite problem I had to manage -- I had 8 codecs
that needed to appear as a single card, over a single TDM bus.

I could not find a good way to do it, so i did it in a bad way, by modifying
the codec driver to appear to the kernel as a single codec, but drive all 8
codecs directly from a single instantiated codec.

The sticky point that I couldn't find a good resolution to, is that the
dai_link specifies a physical connection from CPU to codec.  However, it's a
point to point link, which does not allow for multiple codecs on the same
active dai link at the same time.  the sound/soc/soc-core.c does does not
currently start multiple codecs when starting a card (as far as I can tell).

i think you can create 8 dai_links, but I don't suspect you'll be able to
open all 8, at the same time.

What's the point of doing this anyway?  Why do you want it to appear as 8
sound cards?   It seems that you can manage the 8 channels from user space
easily enough.


On Tue, Jun 21, 2011 at 10:15 AM, Jason Fox <jfox at gai-tronics.com> wrote:

> Hello everyone,
> I am looking for some help where I need an AD193X codec to be shared
> between 8 audio streams using one SSC channel on an AT91SAM9263, in
> other words, I need it to look like 8 different soundcards.  We have the
> 8 TDM channels working in the driver but I can't figure out how to
> create the proper interface of 8 soundcards for ALSA.  In an earlier
> email in this topic was posted:
> > I would instantiate one driver with 3 pcms. This would allow:-
> >
> > pcm0: 2 channel, slot 0,1
> > pcm1: 2 channel, slot 2,3
> > pcm2: 4 channel, slot 0,1,2,3
> >
> > Giving full flexibility for many use cases. The pcms would be mutually
> > exclusive (enforced by machine driver).
> >
> > HTH
> >
> > Liam
> I think that maybe that I want to instantiate one driver with 8 pcms.
>  Where/how do I
> instantiate the PCMs?  I guess it in in the machine driver?
> This is our first attempt at developing a Linux based system so please
> forgive my
> newbie question.  I am sure this is really simple but I'm not following
> somewhere.
> Thanks for your help,
> Jason Fox
> GAI-Tronics
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