#10858 BLOC 1.5-har: Rev L motherboard on XO 1.5 hangs

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#10858: Rev L motherboard on XO 1.5 hangs
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           Reporter:  saadia    |       Owner:  wad           
               Type:  defect    |      Status:  assigned      
           Priority:  blocker   |   Milestone:  1.5-hardware-C
          Component:  hardware  |     Version:  not specified 
         Resolution:            |    Keywords:  1.5           
        Next_action:  diagnose  |    Verified:  0             
Deployment_affected:            |   Blockedby:                
           Blocking:            |  
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Comment(by wad):

 Shame on me for not documenting the end of this saga.

 The problem was most evident when ESD testing the system.  At several
 touch points, an ESD strike was likely to induce the hang described in
 this ticket.  Thanks to a month of diligent engineering work by Gary
 Chiang, the root cause was discovered.

 The root cause of this problem was insufficient ground connection between
 the processor and the Vcore regulator.   A new Vcore regulator, the
 ISL6218, was introduced in a Rev. J motherboard which was just entering
 production.  It was then used in the Rev. K (prototype only), Rev L, and
 further XO-1.5 motherboards.

 A small number of laptops were shipped which would be susceptible to this
 problem.  It was never reported from the field.  They were fixed through
 firmware disabling C3/C4 states.  The difference in power consumption
 between C2 and C4 is around 30 mW, and we strive to go into S3 almost
 immediately instead...

 A larger number of Rev. L motherboards were produced, but these were ECO'd
 at the factory to fix this problem (by adding additional ground
 connections).

 A new motherboard layout, Rev. M, fixed this problem w. a motherboard
 layout change.

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Ticket URL: <http://dev.laptop.org/ticket/10858#comment:11>
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