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Mar 07 2010

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plug instability

I’m still having a variety of problems with my sheevaplug. Not least of which is the fact that SDHC cards don’t seem to be the best choice of boot medium. I have had failures with two cards now and some searching of the various on-line fora suggests that I am not alone here. In particular, SD cards seem to suffer badly under the read/write load that is routine for an OS writing log files – let alone one running a file or web server. I have also had several failures with my external USB drive. It seems that the plug boots too quickly for the USB subsystem to initialise properly. This means that there is not enough time for the relevant device file (/dev/sda1 in my case) to appear before /etc/fstab is read to mount the drive. A posting on the plugcomputer.org forum suggested a useful workaround (essentially introducing a wait), but even that was only partially sucessful. Sometimes it worked, sometimes it didn’t. In fact, the USB drive still often fails after a random (and short) time and then remounts read-only. Attempts to then remount the drive manually (after a umount) result in failure with the error message “mount: special device /dev/sda1 does not exist”.

In my attempts to cure both the booting problems and the USB connection failures I have installed the latest uboot (3.4.27 with pingtoo patches linked to from Martin’s site) and updated my lenny kernel to Martin’s 2.6.32-2-kirkwood in the (vain as it turns out) hope that the latest software would help. Here I also discovered another annoying problem – installing the latest kernel does not result in a new kernel image, the plug still boots into the old kernel until you run “flash-kernel”. Fortunately this is reasonably well known and is covered in Martin’s troubleshooting page.

I will persevere for perhaps another week with the current plug configuration. If I can’t get a stable system though I will try installing to USB drive (perverse as that may seem) and changing the uboot to boot from that rather than the flaky SD card. Most on-line advice suggests that USB support in uboot is rather “immature”, but it can’t be any worse than the current setup. My thinking is that if I can introduce a delay in the boot process by uboot so that I can successfully boot from an external HDD, the drive connection might then be stable enough to be usable.

Of course I could be completely wrong.

Permanent link to this article: http://baldric.net/2010/03/07/plug-instability/