#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:  code                 |    Verified:  0                                      
Deployment_affected:                       |   Blockedby:                                         
           Blocking:                       |  
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Comment(by Quozl):

 Tested SanDisk 4G microSD class 2 in XO-1.5 with oscilloscope attached to
 VCC_SD.  Measured minimum voltage after certain off times:

 ||''power-off-time''||''voltage''||
 ||40ms||1.2V||
 ||60ms||0.8V||
 ||80ms||0.6V||

  * this particular card does not require the specified ''less than 0.5V
 for 1ms'', but seems happy with less than 1.2V for 1ms,
  * there's a reduction of the rate of discharge, at around 1.2V, which is
 presumably when the card shuts down,
  * the 45ms mark in the previous test correlates to the inflection point
 in the curve.

 Testing further, we need about 200ms to meet the specification of ''less
 than 0.5V for 1ms'' with this particular card, but the result will be
 different over card type and operating temperature.

 We have a choice:
  * increase the delay, and wear the startup or testing performance hit
 that will result, or;
  * turn the card on and do not turn it off until control is passed to an
 operating system kernel, and wear the risk of unintended consequences.

-- 
Ticket URL: <http://dev.laptop.org/ticket/10512#comment:3>
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