#12588 BLOC 13.2.0: XO-4 max volume produces distortion

[Zarro Boogs per Child]

#12588: XO-4 max volume produces distortion
------------------------------------+---------------------------------------
           Reporter:  dsd           |       Owner:  dsd                              
               Type:  defect        |      Status:  new                              
           Priority:  blocker       |   Milestone:  13.2.0                           
          Component:  kernel        |     Version:  Development build as of this date
         Resolution:                |    Keywords:  XO-4 Speaker Audio               
        Next_action:  add to build  |    Verified:  0                                
Deployment_affected:                |   Blockedby:                                   
           Blocking:                |  
------------------------------------+---------------------------------------
Changes (by dsd):

  * next_action:  code => add to build


Comment:

 XO-1.75 and XO-4 use different volume control techniques.

 The XO-1.75 driver effectively hardcodes the speaker volume (reg 2,
 actually it can be changed in alsamixer but not in regular UI) and drives
 the DAC volume register (reg 10) to change volume levels.

 The XO-4 driver hardcodes the DAC volume register and the volume control
 slider exposed in the UI controls the speaker/headphone volumes (reg 2 and
 reg 4).

 So matching the registers as I had tried to do before is not a valid way
 to approach this bug.

 I don't have an XO-4 C2 unit to test, but I have pushed a kernel change
 (4016fa1d6) which should help, it disables the speaker gain and drops the
 hardcoded DAC volume a bit, it sounds better on my B1.

-- 
Ticket URL: <http://dev.laptop.org/ticket/12588#comment:8>
One Laptop Per Child <http://laptop.org/>
OLPC bug tracking system