Comment 7 for bug 626907

I haven't looked at the TRM so far, but my experience is that the boot FAT partition must start at sector 63 and must probably be (n*255-1)*63 sectors in size, where n is an integer >=5. In addition, only FAT32 appears to work. Furthermore, the "geometry" described by the partition table must be 255x63. I haven't managed to get any other configuration booting on Beagle xM.

I have succeeded in booting a card matching the above constraints, and where the FATs and data area are 4MB aligned (SD card style). So it looks like the FAT fs handling in the boot firmware sane, but the partition handling is not, at least for some boards.

It would be quite simple to modify mkdosfs to allow creation of filesystems with different internal alignment as above, but it doesn't support this natively at present -- instead, I had to build an initial fs and then tweak it in a hex editor. However, this is probably not very useful, since the boot partition is pretty much write-only for us (and not written very often).

I wasn't successful so far in moving the FAT partition to another location, but it's probably worth persevering due to the obvious value of freeing up the first 8MB for real uses.