Ticket #10512 (closed defect: fixed)
XO-1, XO-1.5 and XO-1.75 A1 external SD card slot does not discharge supply
|Reported by:||Quozl||Owned by:||Quozl|
|Component:||ofw - open firmware||Version:||1.5/1.0 Software Build os852 aka 10.1.2|
|Action Needed:||no action||Verified:||no|
|Deployments affected:||Blocked By:|
Description (last modified by Quozl) (diff)
- 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 to power-off-time
Level 2 fix: add discharge clamp to external SD card slot voltage. Completed for XO-1.75 A2 schematics.