XO-1 OFW occasionally has difficulty reading from my "permanent" SD card

James Cameron quozl at laptop.org
Sun Mar 13 19:22:28 EDT 2011

G'day Mikus,

Fristly, use disable-security so that the developer key is not required
to be present.  Is there a good reason for not disabling the security
system?  However, if you are booting the laptop from the SD card this
may merely move the problem from developer key recognition to booting.

Secondly, there is a design oversight in the XO-1 powering of the SD
card, in that the laptop does not force the power off quickly enough
(#10512); the power can remain at a voltage that can trigger
unpredictable behaviour of an SD card.  This wasn't much of a problem
with SD cards some years ago, but I have found more reports of it with
modern cards.

OpenFirmware powers off the SD card between the access to the root
directory and the access to the security directory.  It also does the
same between the access to the root directory and the boot directory.

It would take a new release of OpenFirmware for XO-1 to add a workaround
for this.

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

However this doesn't prevent power off events that will occur before
olpc.fth is executed.  That's a good reason to disable-security perhaps,
but there will remain the access to sd:\ and then sd:\boot in order to
read olpc.fth.

I have no explanation for why the external USB cables change the
behaviour of your symptom.

James Cameron

More information about the Devel mailing list