[OLPC-devel] Re: ALSA interface for the analog input

[Jim Gettys]

On Thu, 2006-07-06 at 12:39 -0400, Jaya Kumar wrote:
> On 7/6/06, Jim Gettys <jg at laptop.org> wrote:
> > Jaya,
> >
> > I know it will be a little bit until we have the embedded controller
> > code for the analog input on the codec done.
> >
> > I was wondering what sort of ALSA interface should exist (if any) for
> > such a feature, or whether the interface for the analog input control
> > should be elsewhere.
> 
> I would recommend using mixer controls. This surfaces the capability
> of switching into DC sensor mode (turning off Vrefout and disabling
> the high pass filter Miller found) to user level applications via the
> standard alsa mixer api. That's how other AC97 codecs and other AC97
> codec specific features are handled. Scripted applications can call
> amixer directly to switch into that mode if they wanted to avoid
> directly pulling in alsa libs.
> 
> By the way, as I had promised before, the patch that does the above is
> already in ALSA. :-)

> http://git.kernel.org/git/?p=linux/kernel/git/perex/alsa-current.git;a=commit;h=02856b5684677b74095069c3be4774c2992e4fdc
> 
> Thanks,
> jaya

Ah, wonderful.  So all we have to do is plug in a routine to do the deed
on our hardware...

That begs an interesting question: we have to poke a register on the ADI
1888, and also tell the embedded controller to do something, to enable
the analog input.

Is this going to pose any difficulties?  One piece of it is potentially
generic, and the other is clearly very OLPC hardware specific....
                                     Regards,
                                        - Jim

-- 
Jim Gettys
One Laptop Per Child