#12916 NORM Future : alc5631 pops at capture start

[Zarro Boogs per Child]

#12916: alc5631 pops at capture start
-------------------------------------+-------------------------------------
     Reporter:  Quozl                |                 Owner:  Quozl
         Type:  defect               |                Status:  new
     Priority:  normal               |             Milestone:  Future
    Component:  kernel               |  Release
     Keywords:                       |               Version:  Development
     Blocking:                       |  source as of this date
Action Needed:  review               |            Blocked By:
                                     |  Deployments affected:
                                     |              Verified:  0
-------------------------------------+-------------------------------------
 Pops, or unplanned signal swings, are at the start of captures made
 through the microphone or input socket on the XO-1.75 and XO-4.

 See also #9640 for similar problem on XO-1.5.

 See also #12289 for a test method for DMA that relies on the pops.

 Is mostly solved on XO-1.75 by moving the register changes to the
 ''.startup'' operation, followed by a small delay of 340ms.  The register
 changes that cause pops are;
  * turning on Vref,
  * turning off Vref fast,
  * turning on the record mixer block,
  * turning on the microphone bias block,
  * turning on the microphone boost gain block,
  * turning on the ADC block, and;
  * turning on i²s serial data port,

 That pops are also caused by the microphone boost gain block and i²s
 serial data port was not properly handled by the released driver in 13.2.5
 and earlier.

 Test case: present silence or a test tone to the laptop under test, then
 run arecord at all sample rates, both mono or stereo, play back the files,
 and examine the files using audacity.

 {{{
 for rate in 8000 11025 16000 22050 32000 44100 48000 88200 96000; do
   for channels in 1 2; do
     arecord --file-type=wav --channels=$channels --format=S16_LE \
         --rate=$rate --duration=1 /tmp/x.$channels.$rate.wav
     sleep 2
     aplay /tmp/x.$channels.$rate.wav
   done
 done
 }}}

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Ticket URL: <http://dev.laptop.org/ticket/12916>
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