#9514 NORM Not Tri: XO-1.5 - Audio driver needs to bias DC Mic port at midpoint

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#9514: XO-1.5 - Audio driver needs to bias DC Mic port at midpoint
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 Reporter:  wmb at firmworks.com  |                 Owner:  dsaxena      
     Type:  defect             |                Status:  new          
 Priority:  normal             |             Milestone:  Not Triaged  
Component:  kernel             |               Version:  not specified
 Keywords:                     |           Next_action:  never set    
 Verified:  0                  |   Deployment_affected:               
Blockedby:                     |              Blocking:               
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 The following is from Gero Leonardo at Conexant:

 Because Port-F is DC coupled (for possible DC coupled input), the input
 signal must be centered with the DC input range of the CODEC, therefore
 the MIC_BIAS must be set to 50% of AVDD (1,65V), the codec currently sets
 it to 80% (+2.67V), therefore I provided external bias source set at
 +1.65V. I also had to AC couple the Audio Precision into the MIC jack to
 prevent the low output impedance from the tester from pulling down the
 input signal towards ground. Normally with don't have to worry about these
 items if all codec inputs are AC coupled. In any case, if you are using a
 floating microphone into the jack, you won't have any problem. Voice
 recordings and playbacks sound nice and clean from the external jack and
 the internal MIC as well.

 Regarding software driver, do you still plan to do some Linux driver
 development to optimize power consumption ?
 If so, need to change setting for MIC_BIAS_B to 50% as I mentioned above
 (needs to be done in any case).
 Also, on capture I suggest turning on the MIC_BIAS_B and delay the stream
 capture until MIC input settles out, this is to avoid some pop at the
 beginning due to MIC_BIAS_B turning on.

 (assigning to kernel although it's probably really an ALSA driver issue,
 for which there is no obvious component in trac)

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Ticket URL: <http://dev.laptop.org/ticket/9514>
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