XO-1.5 microphone testing
wmb at laptop.org
Fri Jul 3 23:46:01 EDT 2009
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
> 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
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