[LAU] Sound from/to custom ADC/DAC

[Chris Obbard]

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