Hi,
I've added a little information the the serial protocol the E2's PBL bootloader talks over UART0.
http://inputplus.co.uk/ralph/emailer/
(Sorry for the `drip, drip' of emails rather than one all-encompassing one, but I don't want to hold releasing information if I suffer from lack of time.)
A later version of PBL is used in the E3 according to Jonathan's dmesg output.
Cheers,
Ralph.