#12348 LOW 13.2.0: [CL4]Power on system and press volume hot key, there will be noise from loudspeaker.

Zarro Boogs per Child bugtracker at laptop.org
Fri Jul 5 21:58:29 EDT 2013

#12348: [CL4]Power on system and press volume hot key, there will be noise from
           Reporter:  tomyin               |       Owner:  Quozl               
               Type:  defect               |      Status:  assigned            
           Priority:  low                  |   Milestone:  13.2.0              
          Component:  ofw - open firmware  |     Version:  Development firmware
         Resolution:                       |    Keywords:                      
        Next_action:  package              |    Verified:  0                   
Deployment_affected:                       |   Blockedby:                      
           Blocking:                       |  
Changes (by Quozl):

  * next_action:  diagnose => package
  * milestone:  4-firmware => 13.2.0


 Reproduced Q7B35 and Q4D32.

 The noise sounds like buffer underrun.

 Same noise sound also occurs if startup sound is used after boot:
 ok sound sound-end many

 Before the noise, ''sound'' has begun playback, and an interrupt service
 routine is doing audio buffer reload at 333 Hz.

 At about the time of the noise, ''sound-end'' is waiting for the playback
 to finish, with interrupts disabled, and using a preset audio buffer
 reload rate of 100 Hz.

 Patching ''wait-sound'' to sleep shorter intervals fixes the artificial
 ok dev /audio
 ok 9 a npatch wait-sound
 ok dend
 ok sound sound-end many

 Solution A: leave the interrupt rate at 333 Hz, and increase the ''sound-
 end'' non-interrupt rate to 333 Hz.  Reduced frequency to 1 in 6 key

 Solution B: increase the interrupt rate to 500 Hz, and increase the
 ''sound-end'' non-interrupt rate to 500 Hz.  Reduced frequency to 1 in 50
 key presses.

 Theory: it is a kind of race.  The key press to change the sound volume
 changes the duration or position of the keyboard interrupt relative to the
 audio buffer reload interrupt.

 Fixed in [http://tracker.coreboot.org/trac/openfirmware/changeset/3685 svn

Ticket URL: <http://dev.laptop.org/ticket/12348#comment:5>
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