by summers » Tue Apr 10, 2018 9:56 am
Its a question on which board.
Many arm board have a boot rom of some kind, but not all. The boot roms have various functionality to boot from various devices. For most though what usually ends up happening is they start executing external storage from the start.
That in arch, usually (but not always) goes via a first stage u-boot, thats often called MLO. This sets up the processor such that it basically functional, then it loads up the main u-boot. That then boots linux.
Now MLO and u-boot will normally be in *specific* places on the external storage, that why they get "dd"ed straight to the device at a specific location.
Oh yes, armv8 often goes via secure boot - that means that the MLO at least needs to be signed, and booting goes via various levels with various levels of authority.
Now how the pogoplug works - alas I can't say, I don't have one. But for back up purposes as well as /sda1, you'll also need to copy the first handful of bytes of /sda that contain the MLO, and u-boot. If you check the install instructions for pogoplug - its usually just a case of reversing that ...
And added later for the pogoplug it boots from the nand flash that you access on /dev/mtd0. It just has a uboot + environmental variables.