#9423 NORM 1.5-fir: Stabilize OFW USB handling on XO-1.5

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#9423: Stabilize OFW USB handling on XO-1.5
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           Reporter:  wmb at firmworks.com    |       Owner:  wmb at firmworks.com
               Type:  defect               |      Status:  closed           
           Priority:  normal               |   Milestone:  1.5-firmware     
          Component:  ofw - open firmware  |     Version:  1.5-B2           
         Resolution:  fixed                |    Keywords:                   
        Next_action:  test in release      |    Verified:  0                
Deployment_affected:                       |   Blockedby:                   
           Blocking:                       |  
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Changes (by wmb at firmworks.com):

  * milestone:  1.5-software => 1.5-firmware


Comment:

 I am convinced now that the problem with the Kingston DataTraveler stick
 is related to descriptor polling.

 I changed the timing of the descriptor polling routine.  It has an initial
 delay before it starts polling, then an interval between polls.  Normally
 the initial delay is 50 microseconds and the interval is 1 millisecond.

 {{{
 Initial  Interval   Failure Rate
 50 uS      1 mS     one failure per 8 tries, average
 60 mS      1 mS     never fails
 20 mS      1 mS     one in 8, average
 20 mS     10 uS     fails every time
 }}}

 The Kingston DataTraveler takes 44 mS (observed on analyzer) to respond to
 the transaction (time from first NAK'ed IN to successful ACK'ed IN), so
 the 60 mS
 "never fails" case means that the CPU is not polling the descriptor area
 until
 after the transaction is finished.

 In the other (failing) cases, the CPU is polling during the transaction.

 By increasing the polling rate (10 uS interval), the failure can be made
 to happen
 every time.

-- 
Ticket URL: <http://dev.laptop.org/ticket/9423#comment:12>
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