#9776 HIGH 1.5-har: XO-1.5 B3 only boots when serial port connected

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#9776: XO-1.5 B3 only boots when serial port connected
---------------------------------+------------------------------------------
           Reporter:  wad        |       Owner:  wad           
               Type:  defect     |      Status:  new           
           Priority:  high       |   Milestone:  1.5-hardware-C
          Component:  hardware   |     Version:  1.5-B3        
         Resolution:             |    Keywords:                
        Next_action:  reproduce  |    Verified:  0             
Deployment_affected:             |   Blockedby:                
           Blocking:             |  
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Changes (by wmb at firmworks.com):

  * owner:  wmb at firmworks.com => wad
  * component:  ofw - open firmware => hardware


Comment:

 I'm changing the component from ofw to hardware because the following
 line:

   With no serial port connected to the CPU port, no POST codes are
 reported by the EC

 tells me that the OFW startup code is not getting a chance to run.

 OFW issues this post code sequence - 01, 03, 0f, 10, 1d - in quick
 succession as CPU instruction execution begins.  Normally the EC only
 reports the 1d because it can't poll fast enough to display them all.  If
 the EC shows none at all, it means that there were no port80 writes.  The
 first post code - 01 - happens on the fifth machine instruction after
 execution begins.  If the program counter isn't getting that far, there is
 nothing I can do in OFW to help with this problem.

 This sentence:

   The connected serial port must be powered on to have a positive effect.

 makes me wonder if the serial port could be back-powering some rail that
 is otherwise unpowered.

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Ticket URL: <http://dev.laptop.org/ticket/9776#comment:2>
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