[PD] I2S audio possibilities

[Simon Wise]

On 04/02/15 05:30, Miller Puckette wrote:

> In an ideal world someone would build us an I2S expansion board for Pi
> with 8CH audio in and out, memory mapped straight to user space.  Maybe
> someday someone will build that :)

the wolfson cards have some of that, and quite a bit of control internally, with 
lots of sync possibilities and so forth, even programmable dsp routines if you 
really want! The drivers supplied are for alsa and work fine with pd, and expose 
their internal mixing options etc in the alsa interface ... but the Pis don't 
expose the 8ch I2S on their pins, only 2ch ones, so though the wolfson card can 
take 8ch in the pi can't deliver it ... I guess the 8ch I2S interface is going 
to the hdmi circuitry.

The B version uses almost every available pin, including the extras in p5, but 
the B+ version doesn't need all the new ones.

I can put an image up on dropbox of a system for the B version with the modules, 
scripts etc working nicely, and an RT kernel, if that is useful, that has been 
well tested. The images on the wolfson site were not working for me, but I found 
a version that worked. I haven't got a B+ wolfson card so can't verify them.

One issue for me is that I'd like to play the audio from AV files through them, 
but the players I am using send audio directly out, and I am not able to send it 
to userspace, alsa and pd ... so can't use the wolfson audio in those cases.

It should be possible, for example, to daisy-chain several pis with wolfson 
cards via the wolfson SPDIF I/O ... then the clock source can be all from the 
first wolfson, and the SPDIF chain ending up with a digital stereo mix output 
from the last wolfson, all the mixing and clocking options are available via 
alsa. Testing that is next on my list.


Simon