I went through the source code and came up with this.
First open the USB port at 57600 baud
First you send it "!!!"
it gives you a welcome message
ATmegaBOOT / Arduino Mega - (C) Arduino LLC - 090930
Then you can type
t Toggle LED
r Read byte from address xx (x is a BINARY value)
u loop back, continuous loop to echo back what every you send
b external Bus, does something with external memory
j Jump to user program, same as doing nothing.
It not a real good monitor, it doesnt do much, it is limited in size
It is only compiled for
AVR_ATmega128 and
AVR_ATmega1280
I added AVR_ATmega2560
The monitor has a very short timeout. If you dont type something it goes back to waiting for download and then will start the user program if it exists
Mark