Hi Roberto:
There's no problem with that. My code stays in the loop until key is
depressed. In your code you have to go in a loop after key is depressed and
you have to stay in the loop until the key is pressed again. Before to go in
this loop you have to set flags modify_up or modify_down. These flags are used by interrupt timer0 to blink the line. Be carefull with rising and
falling down edge. You don't have to go in loop until key is depressed and
you don't have to leave it until key is depressed the second time.

Regards,
Alberto