#9604 NORM 1.5-sof: build DC sensor mode on audio driver

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#9604: build DC sensor mode on audio driver
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           Reporter:  Quozl     |       Owner:  dsd              
               Type:  defect    |      Status:  new              
           Priority:  normal    |   Milestone:  1.5-software-beta
          Component:  kernel    |     Version:  not specified    
         Resolution:            |    Keywords:                   
        Next_action:  diagnose  |    Verified:  0                
Deployment_affected:            |   Blockedby:                   
           Blocking:            |  
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Comment(by Quozl):

 Reviewed schematics, pg 20, AUDIO_CODEC.

  * the resistance value I deduced matches the series resistance of R9 (470
 ohms) and R7 (3k4).

  * the emitted voltage values match what should be seen when signal B_BIAS
 raised during ''arecord'', and returned low when ''arecord'' stops.

  * B_BIAS is also being raised for a short time when the master volume
 control is muted or unmuted.

 Reviewed Measure source code changes made for XO-1.5 support, using
 repository
 git://git.sugarlabs.org/measure/XO_1_5_support.git

  * there was no change to the method by which samples are read from the
 sound device,

  * there were some minor changes around setting mixer values.

 Reviewed Measure interface to audio hardware;

  * it uses gstreamer to read audio samples,

  * apart from manipulating mixer settings Measure does not change how it
 captures samples when in DC mode.

 Therefore my use of ''arecord'' for analysis of the system at kernel and
 hardware level is reasonable, and I can continue to use that method.

 Summary: on os51, in DC mode, DC samples are unchanging despite input
 voltage being changed.  It is as if the analog voltage is not reaching the
 kernel.  I can't see any way they wouldn't be reaching the codec, given
 that AC samples certainly do.

-- 
Ticket URL: <http://dev.laptop.org/ticket/9604#comment:14>
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