Mic input

[Jaya Kumar]

On 10/11/06, Bert Freudenberg <bert at freudenbergs.de> wrote:
> The only documentation I could find is in a mailing list thread
> (http://mailman.laptop.org/pipermail/devel/2006-July/000672.html):
>
>         *a- tell the EC to turn on MIC_AC (ie: bypass C35 and R25) [ OLPC
> specific ]
>         *b- tell ALSA to disable VREFOUT and the high pass filter [ AD1888
> specific ]
>
> So how do I "tell the EC to turn off MIC_AC"?
>

By default, ALSA AD1888 sets things into the appropriate mode for
standard mics. You won't need to affect those mixer controls for
regular mics. That is, VREFOUT is enabled, and the high pass filter is
enabled. You asked a good question for users who want to use analog
input mode, which is how do you tell the EC to turn off MIC_AC. For
the A-Test board, Ray sent a sequence of IO read/writes that instruct
the EC to turn off MIC_AC. I've pasted them here:

> outp(0x381, 0xFC);
> outp(0x382, 0x10);
> mic_reg = inp(0x383);
> outp(0x381, 0xFC);
> outp(0x382, 0x10);
> outp(0x383, mic_reg | 0x40);       // GPIO06 : bit6. 1: Enable output , 0: Disable Output
> ;
> outp(0x381, 0xFC);
> outp(0x382, 0x20);
> mic_reg1 = inp(0x383);
> outp(0x381, 0xFC);
> outp(0x382, 0x20);
> outp(0x383, mic_reg1 | 0x40);      // GPIO06 : bit6.       1: high , 0: Low

Currently, I haven't figured out a clean way to expose the above EC
functionality. Everyone is welcome to work on it and submit a patch.
:-)

Best regards,
jaya