#12660 NORM 13.2.0: XO-1.5 time reset problem with year

[Zarro Boogs per Child]

#12660: XO-1.5 time reset problem with year
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           Reporter:  dsd                  |       Owner:  Quozl        
               Type:  defect               |      Status:  new          
           Priority:  normal               |   Milestone:  13.2.0       
          Component:  ofw - open firmware  |     Version:  not specified
         Resolution:                       |    Keywords:               
        Next_action:  design               |    Verified:  0            
Deployment_affected:                       |   Blockedby:               
           Blocking:                       |  
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Changes (by Quozl):

  * next_action:  never set => design


Comment:

 The cause of the problem is that the battery dead bit is not reliable, and
 the year 6500 is from the reset value of the century register; 0xff.

 Regarding the battery dead bit:
  * the chipset provides a clock that behaves ''like'' a DS1385,
  * the battery dead bit on the DS1385 and the chipset is not latching,
  * in other designs, an external non-rechargeable battery is attached,
  * our XO-1.5 provides both clock battery and main bus power to the clock
 power input, so at the time we sample the battery dead bit the clock power
 input is good,
  * therefore the battery dead bit is not useful for detecting loss of
 clock data.

 A test of an XO-1.5 with no clock battery, with varying power off times
 was run, from between 1 and 64 seconds, capturing the clock registers at
 power up.  200 cycles were done.

 Several behaviours were found to correlate to power loss:
  * the date and time resets to 01-01-01 01:01:01, and continues to count,
 (after 5 seconds and before 22 seconds without power),
  * the date and time resets to 00-00-00 00:00:00, and may continue to
 count, the divider configuration will clear, the interrupt configuration
 may clear, and the 24/12 hour format register bit will clear, (after 22
 seconds without power),
  * the day of week register may be set to 0x10, (after 26 seconds without
 power).

 It should be possible to detect power loss based on these behaviours.

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Ticket URL: <http://dev.laptop.org/ticket/12660#comment:1>
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