Fwd: [OLPC-devel] Geode GIT Tree
simon at schampijer.de
Fri Jun 16 21:37:40 EDT 2006
What we did so far:
- We toggled a pin on the embedded controller chip. (at least we hope
- and made the software changes, means:
- used the snd debug enabled kernel
- set the AC97 to the following:
echo "76 6424" > ac97#0-0-+regs
So you mean we should be able to use the analog input by now?
Thanks very much for your description,
Mark J. Foster wrote:
> Hi, Simon,
> The stereo output is completely independent from anything else. The
> internal or external microphones are switched by using a switched mic
> jack - it automatically disconnects the internal microphone when a
> jack is inserted into the mic in socket.
> The VREF output should normally be on (controlled by the AD1888's
> registers, as mentioned in the data sheet) - this provides DC power to
> the microphone. To enter sensor mode, two things must happen.
> First, the VREF_OUT voltage must be turned off via software. This
> leaves a plain AC-coupled input into the sound chip. The second step
> is to toggle a pin on the embedded controller chip - this pin connects
> an analog switch across the input capacitor, which changes the
> microphone input from AC-coupled into DC-coupled. Unfortunately,
> until we have EC code, this second step cannot be performed without
> hardware mods. As a result, the best we can do right now, until we
> get EC code, is an AC-coupled input.
> Simon Schampijer wrote:
>> Hi Marc,
>> in an earlier email you described the changes needed to be made to
>> have the DC-coupled, normal A/D input.
>> You said: "... The other step is software - you'll need to turn off
>> the AD1888's external VREF_OUT function ..."
>> To have the microphone we have to enable "the AD1888's external VRef
>> output, which supplies power to the microphone."
>> I am a bit confused - how do you switch than the two functionalities?
>> Can you explain those bits for a non hardware guy? Am I right that we
>> are able to access the following devices on the board:
>> - stereo out
>> - mono in (line level) / analog in
>> - built in mic (where would the connection for that be on the board)
>> Or am I confusing some bits?
>> Thanks very much
>> Mark J. Foster wrote:
>>> Hi, Chris!
>>> If the mic in jack does not work with a mic, but it does work with a
>>> line input, then the audio driver has probably not properly enabled
>>> the AD1888's external VRef output, which supplies power to the
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