[LAU] Sound from/to custom ADC/DAC

[pepijn de vos]

Hey all,

Meanwhile the Beagle Bone arrived so I'm finally testing with that.
I'm still struggling to write a correct overlay for it.

On the Pi I used an overlay based on the generic simple-audio-card,
spdif-receiver and spdif-transmitter.
https://github.com/pepijndevos/ouisician/blob/master/soc/fpgai2s.dts

On the Beagle I found this one I linked to earlier:
https://github.com/ctag-fh-kiel/ctag-face-2-4/blob/master/device-tree-overlays/BB-CTAG-FACE-4CH-00A0.dts

This one seems at least useful for setting up the pinmux and mcasp.
However, it uses the specific ctag,face-2-4 card with the analog,ad1938
codec.
Instead I would like to use the generic cards I also used on the Pi (or
similar).

Is there a way to connect simple-audio-card with mcasp?
Or do I really have to write a custom card in C?

Regards,
Pepijn

On Wed, Mar 14, 2018 at 10:33 PM, Chris Obbard <chris at 64studio.com> wrote:

> Hi Pepijn,
>
> > Thanks for the advice so far.
> > Based on this post, I managed to make my own I2S overlay.
> > https://www.raspberrypi.org/forums/viewtopic.php?t=189152
> >
> > However, still only two channels.
> > I found that the Pi can in fact understand TDM, but the SoC can only get
> 2
> > of the channels for some reason.
> > https://github.com/raspberrypi/linux/pull/1982
>
> Yep, two channels only for Pi. It's after all a consumer SoC designed
> for mobile phones.
> I am not sure how the Audioinjector Octo works but this has eight channels.
> It uses a gate array with some kind of strange multiplexing. I have
> added Matt, he will be able to explain more on the design ;-).
>
> > For the Beagle Bone, I also found someone who makes a cape with a lot of
> > inputs and outputs.
> > There are some forum post scattered here and there with references to
> McASP,
> > as you mentioned.
> > This overlay seems a good starting point, potentially:
> > https://github.com/ctag-fh-kiel/ctag-face-2-4/blob/
> master/device-tree-overlays/BB-CTAG-SW-8CH-00A0.dts
> >
> > So to sum it up, I2S works on the Pi for 2 channels, Beagle Bone is
> > something to look at more closely.
>
> We are working with a university who have designed a Beaglebone cape
> and I have written kernel driver for soundcard with up to 6
> input/output channels designed for hearing aid research.
> Please wait kindly and I will post a link to the Github page in coming
> days with full hardware layout and kernel patch.
>
> BR,
> Chris
>
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