My question is actually whether it is possible to carry out a Canon firmware update without a Canon menu?
For example, if parts of the firmware in the camera are destroyed.
If the main firmware is able to start a diskboot.bin, one could create a special one that is able to reflash the damaged areas. If the damage is extensive enough, many parts of the rom would need to be copied to make diskboot functional.
In some cases (erased or damaged main fw start), the bootloader can also resort to starting diskboot.bin - if it finds one on card.
AFAIK the bootloader cannot deal with firmware update files.
