Hi Erik,

I think also, Jacek method was the best.
Use an extra small micro, to listen on the serial bus for a magic word and bring the main CPU into its programming state.
I think, the ATtiny12 was good (6 I/O available in a small 8 pin case), but I'm still unable to get.

Otherwise on using the main CPU to program itself, was equal risky than updating your motherboard BIOS.

Additional such supervisor can also receive a remote reset command in case, if the main CPU hangs and no human beside to switch off the gadget.


Peter