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

[Zarro Boogs per Child]

#10512: XO-1.5 and XO-1.75 A1 external SD card slot does not discharge supply
---------------------------------+------------------------------------------
 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
 Keywords:                       |           Next_action:  code                                   
 Verified:  0                    |   Deployment_affected:                                         
Blockedby:                       |              Blocking:                                         
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 Reproducer:
  * place an OLPC OS on an SD card, 32G class 10 SanDisk, or 8G class 4
 SanDisk, or others not yet identified,
  * insert the card into the external slot,
  * attempt to boot, the result is that the external card is ignored, the
 internal card is used, or an error appears,
  * or issue OpenFirmware command "dir ext:\security", the result is that
 an error appears:

 {{{
 SDHCI: Error: ISR = 8000 EST = 10 Data Timeout,
 Stopping
 Can't open directory
 }}}

 Single access to directory ext:\ works fine, it is only access to a
 subdirectory or a multiple access as done by ''boot'' that triggers the
 symptom.

 Analysis: the external SD card is not being properly reset, because the
 supply voltage has not achieved the minimum 0.5V for 1ms required by the
 Physical Layer Simplified Specification Version 3.01, because there is no
 discharge clamp for the card supply voltage.

 The external SD card voltage is controlled by the main CPU.  The internal
 SD card voltage is controlled by the embedded controller (EC).  Therefore
 the symptom does not affect the internal SD card.  It only occurs if there
 is an SD card in the external slot.

 The symptom does not occur for all SD cards, only recently manufactured
 cards have shown the symptom.  This suggests that the recent cards draw
 less power.

 The required power off time for an 8G SD class 4 card has been measured to
 vary between 37ms and 68ms, depending on the temperature of the laptop
 (colder requires longer), and which laptop (of a batch of 5) is tested.

 ----

 Level 1 fix: allow for more time for the card voltage to collapse before
 re-powering the card.  The time allowed in q3a61 and lower was 20ms.
 Install OpenFirmware -r2065 or later (q3a61c for XO-1.5), which increases
 this time to 40ms, and if the problem persists increase the power off time
 still further, for example:

 {{{
 dev /sd d# 60 power-off-time
 }}}

 Level 2 fix: add discharge clamp to external SD card slot voltage.
 Completed for XO-1.75 A2 schematics.

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