XO-1 vs Sugar 0.104 performance, and swap to NAND Flash

James Cameron quozl at laptop.org
Wed Apr 8 21:43:38 EDT 2015

On Wed, Apr 08, 2015 at 09:19:14PM -0400, Nathan C. Riddle wrote:
> Can I rephrase the question:
> Put /home and swap on SD.

That might help, for particularly large activities.

> I believe previous posts here have indicated that SD to RAM is not
> the slowest step. This has always been a debate in my mind.  The SD
> simpler in the field.  My 16 GB SD occasionally hangs on boot when
> used with USB to ethernet adapter on battery -- suspect power demand
> issue.

No, it might not be power demand, it is more likely to be timing.

To check, make sure the laptop is unlocked, and add this to the second
line of the boot/olpc.fth file:

    dev /sd  patch 2drop cb! sdhci-card-power-off  dend

This will prevent the firmware from turning off the card reader before
booting Linux.  The card reader will stay powered on.

A 16 GB SD card is modern.  It draws less current than the cards for
which the XO-1 was designed.  The XO-1 SD card reader doesn't have
discharge clamps on the power rails.

When a USB ethernet adapter is present, the firmware takes longer to
probe the USB bus controller.  When on battery, the firmware may take
longer to probe the embedded controller.

The combined effect is to change the timing of power on and power off
events for the card.  Cards are known to be confused if the voltage
does not fall fast enough, and without discharge clamps and with a
modern card, this is more likely.

"occasionally hangs" means you're right on the border of it working or

(p.s. there is some old code around that tries to patch
card-power-off, most recently seen in Jhon Diaz' repost of the Puppy
Linux olpc.fth ... but since card-power-off is now a defer, it doesn't

James Cameron

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