[Trac #1388] setting dcon to "dcon sleep" mode does not shut off panel in pre-b3

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#1388: setting dcon to "dcon sleep" mode does not shut off panel in pre-b3
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 Reporter:  dilinger  |        Owner:  wad    
     Type:  defect    |       Status:  new    
 Priority:  blocker   |    Milestone:  BTest-3
Component:  hardware  |   Resolution:         
 Keywords:            |  
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Comment (by wmb at firmworks.com):

 By George, I think I've found something.

 If I execute the "2 mode!" from the serial console, the panel turns off.
 If I execute it from the XO keyboard, the screen flashes off but then goes
 black again.

 Furthermore, if I turn off the panel from serial (2 mode!), then type a
 key on the XO keyboard, the screen goes black.  It doesn't matter which
 key; I've tried several - space, 'h', arrows, ...

 I have scope probes on VGH (18V to the panel) and VDDEN (logic signal from
 the DCON that turns on the LCD power converters).  When the panel is on or
 black, both those signals are high; when the panel is off, both of them
 are at 0.  A corollary of this is that they go from 0 to high when
 keyboard activity results in panel turn-on.

 Okay, I just had another brainstorm.  I added a delay on the command line
 before turning off the panel, to let the keyboard "quiet down" between the
 time you hit enter to execute the line and when the panel actually goes
 off.  It works; you can turn off the panel from the XO keyboard with this
 technique.

 ok  d# 100 ms  2 mode!  d# 3000 ms  h# 69 mode!

 On the preB2 that I'm using, 100 mS seems to be the magic number.  It
 always works with that amount of delay, and is hit-or-miss with 80 mS.

 I need to probe some more signals to discover the exact wakeup mechanism.

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Ticket URL: <http://dev.laptop.org/ticket/1388#comment:1>
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