XO-1 OFW occasionally has difficulty reading from my? "permanent" SD card [Devel Digest, Vol 61, Issue 38]

James Cameron quozl at laptop.org
Mon Mar 14 19:12:17 EDT 2011


On Sun, Mar 13, 2011 at 11:27:44PM -0700, Yioryos Asprobounitis wrote:
> > You might try patching OpenFirmware to not turn off the
> > card between
> > subsequent accesses.? To do this, assuming you are
> > using Q2E45, add the
> > following early in your olpc.fth file:
> > 
> > ??? dev /sd
> > ??? patch 2drop cb! card-power-off
> > 
> 
> Is this also true for the XO-1.5 q3a62? or is an XO-1-only issue?

The workaround you quoted above is not correct for XO-1.5 Q3A62, it was
correct only for Q2E45.

The root cause of the problem (failure to discharge the power supply to
the card) is also present in XO-1.5 hardware.  This is described in
http://dev.laptop.org/ticket/10512

A workaround is in Q3A62 which increases the time that the firmware
waits after turning off the power to the card.

http://tracker.coreboot.org/trac/openfirmware/changeset/2065 shows the
time was increased from 20ms to 40ms.  This was so that a new batch of
cards in manufacturing would pass testing.

It is not possible for me to predict the behaviour on other cards, since
I don't have them.

This change also adds support for changing the delay:

	dev /sd
	d# 60 to power-off-time

The change is lost on reboot.

-- 
James Cameron
http://quozl.linux.org.au/


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