Upgrade mode provides an alternative boot path suitable for booting a standalone restore/recovery system. It chains to a new bootloader, and the new bootloader then loads kernelcache, devicetree, ramdisk and optionally a display image before booting the kernelcache.
All of the files listed above are expected to be in image3 format, and must be signed and/or personalised.
'rd=md0 nand-enable-reformat=1 -progress'
- the upgrade partition does not exist or cannot be mounted - the file /iBEC does not exist in the upgrade partition - the contents of the iBEC file are not an Image3 file or fail authentication
- the upgrade partition cannot be mounted (e.g. due to NAND format incompatibility) - the files /kernelcache, /devicetree and /ramdisk do not exist in the upgrade partition - the contents of any of these files are not valid Image3, or fail authentication - the kernelcache file does not contain a compressed mach-o kernelcache - the devicetree file does not contain a valid devicetree