Marvell EBU:BootROM recovery

Users that have messed up with the system storage can face an empty console after a reboot, meaning that a recovery is now needed.

Two situations: either the BootROM finds something and runs a bootloader (probably U-Boot) that fails to reach the command prompt; or the BootROM will loop over a few NAND blocks, try to boot from each of them and finally give up and display a message like "Trying UART".

Users of the Armada-38x-AP board should have a look at this note.

In both cases, one should send (at 115200b) the xmodem boot pattern (0xbb 0x11 0x22 0x33 0x44 0x55 0x66 0x77) right after resetting the SoC (tight timing). Then, "NACK" characters should be sent by the BootROM (one per second). This means that the BootROM is ready to receive a recovery image (a U-Boot image flagged "-uart.bin" at the end) that it will load in RAM and run. The loading is achieved by the sx-at91 binary (experience shows that it works better using it from Minicom than directly from a Shell). Once in a "live" U-Boot, one can burn the desired image with the bubt command.