XO-1.5 microphone testing

[Mitch Bradley]

John Gilmore wrote:
>> Basically, for each configuration (external microphone plugged in, and
>> external microphone not plugged in), I'd like to know the following:
>>  - which of the 8 microphones is the one to use
>>  - which ports we can turn off
>>     
>
> In reading the generic Intel HDA codec spec, and comparing it to the
> http://dev.laptop.org/~dsd/20090629/codec0.txt, it seems that the
> "Configuration Default" registers aren't being set up properly by OFW.
>   

That is correct.  Patches welcome...

> These registers define the physical location, color, and type of
> device connected by motherboard wiring to each pin on the codec.
> E.g. "Internal Mic Inside Lid" versus "External Green Headphone Output
> 1/8" Jack on Left side".  It's also easy to specify "Not Connected"
> here.  Normally these would be set at power-on by the BIOS, and then
> read by the software in order to properly label the various audio
> controls.  This design avoids needing separate software driver mods
> (kernel "quirks") for every single model of motherboard or laptop.
> (These register contents are not retained over a full codec
> power-down, so the kernel would probably want to save a copy from boot
> time.)
>
> I hope you'll test with both mono and stereo external microphones.
> The new hardware supports analog stereo input (and mic).  It'd be a
> shame to turn that capability off in software because it was only
> tested with an analog mic.
>
> I think it should be possible to turn the mic bias on and off in
> software (allowing the mic port to be used as "Line In").
>
> It should be possible to turn the headphone output into an unamplified
> Line Out.
>
> Testing the OLPC-specific analog "sensor" input mode would be very
> useful.  Given the stereo input jack, this would give experimenters
> TWO analog inputs.  (Somebody should tell XXX who's uploading
> a bunch of instructions for making analog sensors on the wiki;
> e.g. XXX).
>
> It would also be useful to test the higher sample rates and larger
> sample sizes (24-bit samples, at 192 ksamples/sec outbound or 96
> ksamples/sec inbound).  I've had trouble with those settings on an
> Acer netbook, for example.
>
> If the microphone LED is on a GPIO under software control, independent
> of the hardware's actual ability to listen on the internal mic, then
> the LED isn't providing any useful function.  (In which case that LED
> hole might as well be used for sensing the brightness of the light
> falling on the screen; one of the audio ADC's might be useful for
> that.)
>
> 	John
>