Ok! First step has been made. I've managed to update E-520 body with modified firmware :-) I've made minor modifications to show key hex values while button is pressed.
Yes, it looks like IDA with mn103 module can dissasemble this fw.
But I am not sure about loading address -- I still can't find any sense in the disassembled code
No strings2code matches, no any clues, nothing.
Can you describe your way of disassembling?
Show your patch of update, if it's possible
Maybe symbol table?
P.S. I have no Olympus camera now, but have a lot of different firmwares for it.