[9fans] PWM and audio drivers for Raspberry Pi

[9fans] PWM and audio drivers for Raspberry Pi

[Pedro Coutin]

Hello everyone,

I made a working audio driver for the Raspberry Pi by using the chipset's
PWM device directly.

The sound quality seems pretty acceptable to me.  I managed to play music
and the Doom port from 9front with it.

Since it uses the PWM device, it only works for the TRS stereo jack.  I
believe that the most sensible way to make HDMI audio work is to
make a VCHI(Q) driver, and then an audio driver that interfaces with
that. There's very little, if any, documentation available on this and
the Linux kernel code for it is pretty huge.

Tarball with changed files:
http://acsweb.ucsd.edu/~pcoutin/bcm-audio.tgz

Repository:
https://bitbucket.com/pcoutin/9pi-audio

Man page for PWM device:
http://acsweb.ucsd.edu/~pcoutin/bcmpwm.html

I guess I could extend the PWM driver so that the two channels can be
enabled/disabled separately.

Re: [9fans] PWM and audio drivers for Raspberry Pi

[dante]

Hi Pedro,

That's super-cool, thanks!

Please consider submitting the patch through the right channels.
Since I'm new here, I am not sure if this is correct, but here is what
I found out:

1. as a patch(1) to the contributors. No idea if geoff or jmk are still
working there:
     http://plan9.bell-labs.com/wiki/plan9/How_to_contribute/

2. ask David du Colombier to accept and publish your patch:
     http://www.9legacy.org

Cheers,
Dante

On 23.08.2014 11:32, Pedro Coutin wrote:
> Hello everyone,
>
> I made a working audio driver for the Raspberry Pi by using the
> chipset's
> PWM device directly.
>
> The sound quality seems pretty acceptable to me.  I managed to play
> music
> and the Doom port from 9front with it.
>
> Since it uses the PWM device, it only works for the TRS stereo jack.
> I
> believe that the most sensible way to make HDMI audio work is to
> make a VCHI(Q) driver, and then an audio driver that interfaces with
> that. There's very little, if any, documentation available on this and
> the Linux kernel code for it is pretty huge.
>
> Tarball with changed files:
> http://acsweb.ucsd.edu/~pcoutin/bcm-audio.tgz
>
> Repository:
> https://bitbucket.com/pcoutin/9pi-audio
>
> Man page for PWM device:
> http://acsweb.ucsd.edu/~pcoutin/bcmpwm.html
>
> I guess I could extend the PWM driver so that the two channels can be
> enabled/disabled separately.