#9655 NORM 1.5-sof: soft chirp when using USB devices

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#9655: soft chirp when using USB devices
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           Reporter:  pgf       |       Owner:  wad          
               Type:  defect    |      Status:  assigned     
           Priority:  normal    |   Milestone:  1.5-software 
          Component:  hardware  |     Version:  not specified
         Resolution:            |    Keywords:               
        Next_action:  diagnose  |    Verified:  0            
Deployment_affected:            |   Blockedby:               
           Blocking:            |  
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Changes (by wad):

  * status:  new => assigned


Comment:

 This is processor power supply noise as the processor goes in and out of
 C2/C3/C4 states.  This may be verified by doing the following:

 Edit the /bootpart/boot/olpc.fth file to modify the following line (adding
 the processor.max_cstate=1 option):

  " console=ttyS0,115200 console=tty0 processor.max_cstate=1
 fbcon=font:SUN12x22 video=viafb:viafb_mode=1
 200x900,viafb_bpp=24,viafb_active_dev=LCD,viafb_lcd_panel_id=23
 no_console_suspend reboot=acpi selinux=0" to boot-file

 Now reboot to make this take effect.  You can verify that this is working
 by installing the powertop utility (yum install powertop) and checking to
 see what C-states the processor is entering.

 I find that the noise due to Scratch doesn't go away (isn't due to
 C-states), but the USB noise goes away if the processor isn't allowed to
 enter C3/4 states.

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Ticket URL: <http://dev.laptop.org/ticket/9655#comment:3>
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