Notes on UUB Linux Development

Linux on the UUB is going to be much harder than I thought.

PetaLinux is unfortunately a very, very simple tool – it seems like it’s intended to allow people to get up and running quickly, but not actually be able to configure anything intelligently. For instance, there’s no simple way to configure u-boot. At all. It’s Xilinx’s way, or you get no help at all. So, for instance, each boot you have to sit there for about a minute waiting for a boot attempt on the network to time out. No way to tell it “I don’t want netboot.” Sorry, folks, that’s it.

Running list of things I need to figure out:

  • We really want the rootfs to actually be a filesystem. We can’t afford to have the rootfs be entirely a ramdisk: we’re probably going to need lots of RAM for the actual event buffer. Rough estimates would be something like 144 MB. That’s a third of the RAM on the UUB. If we suck up 128 MB for a RAM disk, that only leaves 112 MB for the actual system to use. That’s really restricted.
  • We do not want to use the standard PetaLinux “flash partition” strategy. It’s really, really bad: it uses raw flash, which means any power failure can trash the entire thing, and uses no wear leveling at all. It’s just a bad idea.
  • The clear winner for flash filesystems is UBIFS, using the UBI (‘Unsorted Block Images’) layer.

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