#10953 BLOC 1.75-fi: XO-1.75 External Mic sense does not work

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#10953: XO-1.75 External Mic sense does not work
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           Reporter:  wmb at firmworks.com    |       Owner:  wmb at firmworks.com
               Type:  defect               |      Status:  new              
           Priority:  blocker              |   Milestone:  1.75-firmware    
          Component:  ofw - open firmware  |     Version:  1.75-A3          
         Resolution:                       |    Keywords:  XO-1.75          
        Next_action:  test in build        |    Verified:  0                
Deployment_affected:                       |   Blockedby:                   
           Blocking:                       |  
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Comment(by wad):

 In an N-channel MOSFET, the voltage at the source must be lower than the
 voltage at the gate for conduction, otherwise there isn't any bias to open
 the channel.

 There are two circuits there, one (LED on when Bias AND int mic) is in
 series with the other (int mic).

 In this case, the default pulldown on GPIO96 at boot was preventing proper
 operation of the "int mic" circuit (but not enough that the LED didn't
 work).  Turning off the pulldown when OFW sets up the pin config allows
 the existing 100K pullup (R363) to operate properly.

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Ticket URL: <http://dev.laptop.org/ticket/10953#comment:6>
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