27 Mar
2018
27 Mar
'18
12:48 a.m.
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-overl…
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(a)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