[Trac #845] Sugar needs support for the SW_LID event

[Zarro Boogs per Child]

#845: Sugar needs support for the SW_LID event
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 Reporter:  JordanCrouse  |        Owner:  dcbw     
     Type:  defect        |       Status:  new      
 Priority:  normal        |    Milestone:  Untriaged
Component:  sugar         |   Resolution:           
 Keywords:                |  
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Comment (by JordanCrouse):

 SW_LID is triggered from input events GPIO26.  On B2, GPIO26 is connected
 to the PWR_BUT_in line which is driven by S1, which is a hall effect
 sensor (part # APX9132ATI-TRL).  Put simply, hall effect sensors detect
 the presence of a magnetic field.  S1 is physically located on the "back"
 (side w/o the CPU) of the board, just above the audio input switch.  When
 the lid is lowered, that side of the board comes into proximity to the
 left corner of the base, which is presumably where the magnet is located.
 On the OLPC, the line is high when the LID is open (no magnetic field) and
 low when it is closed.  We are able to detect this event in B2, because
 PWR_BUT_in was moved from a GPIO on the EC, to a GPIO on the 5536, where
 we can directly access it from the Linux kernel.

 There is an identical hall effect sensor (S2) on the opposite side
 ("front" of the board, just above the horizontal USB port on the left hand
 side).  The positioning is such that when the screen is turned and placed
 into ebook mode, this sensor could detect the same magnetic field used for
 the LID event.  Unfortunately, on B2, the line from this sensor is still
 connected to the EC, and we don't yet have an infrastructure for reading
 it (see #224).  Also note that this sensor only detects proximity, there
 isn't any way to tell if the screen is physically rotated or not.

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Ticket URL: <http://dev.laptop.org/ticket/845#comment:2>
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