#10512 NORM Future : XO-1, XO-1.5 and XO-1.75 A1 external SD card slot does not discharge supply

[Zarro Boogs per Child]

#10512: XO-1, XO-1.5 and XO-1.75 A1 external SD card slot does not discharge supply
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           Reporter:  Quozl                |       Owner:  Quozl                                  
               Type:  defect               |      Status:  new                                    
           Priority:  normal               |   Milestone:  Future Release                         
          Component:  ofw - open firmware  |     Version:  1.5/1.0 Software Build os852 aka 10.1.2
         Resolution:                       |    Keywords:                                         
        Next_action:  review               |    Verified:  0                                      
Deployment_affected:                       |   Blockedby:                                         
           Blocking:                       |  
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Changes (by Quozl):

  * next_action:  code => review


Comment:

 Tested SanDisk 32G SD class 10 in XO-1.5 with oscilloscope attached to
 VCC_SD.  Measured voltage after certain off times, compared against
 previous card:

 ||''time''||''SanDisk 4G microSD class 2''||''SanDisk 32G SD class 10''||
 ||50ms||1.9V||1.1V||
 ||100ms||0.9V||0.9V||
 ||150ms||0.6V||0.7V||
 ||200ms||0.55V||0.51V||
 ||250ms|| ||0.5V||

 Time required to achieve 0.5V was around 250ms.

 Unlike the previous card, this card's discharge curve had several changes
 of gradient, which can be summarised as:

  * at power off, voltage declined from 3.3V to 2.4V over 20ms, (45V/s),
  * then voltage declined more rapidly from 2.4V to 1.4V over 10ms,
 (100V/s),
  * then voltage declined less rapidly from 1.4V to 0.5 over 220ms, (4V/s).

 The 20ms delay used by q3a61 is right on the first change of gradient,
 which is perhaps why this card misbehaved for Quanta.

 Changed delay for external SD power off to 250ms.  -r2076.

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Ticket URL: <http://dev.laptop.org/ticket/10512#comment:7>
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