Fwd: [OLPC-devel] Geode GIT Tree

[Simon Schampijer]

Mark,

What we did so far:
 - We toggled a pin on the embedded controller chip. (at least we hope 
it worked)
- and made the software changes, means:
    - used the snd debug enabled kernel
    - set the  AC97 to the following:
       cd /proc/asound/card0/codec97#0
       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,
Simon



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.
>
> Sorry!
> MarkF
>
>
> 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
>> Simon
>>
>>
>>
>>
>>
>> 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 
>>> microphone.
>>>
>>> Cheers!
>>> MarkF 
>>
>>
>>
>