+ in r29,UDR
+ UART_OUT:
+ sbis UCSRA,UDRE
+ rjmp UART_OUT
+ out UDR,r29
+ reti
+
+
+INT_ROUTINE:
+ ldi r16,0 ; disable int0
+ out GIMSK,r16
+ cpi r17,0xff ; toggle light
+ breq TURN_ON
+ TURN_OFF:
+ ldi r17,0xff ; turn off light
+ ldi r25,0x44 ; D
+ rjmp CONTINUE
+ TURN_ON:
+ ldi r17,0 ; turn on light
+ ldi r25,0x4c ; L
+ CONTINUE:
+ out PORTB,r17
+ sbis UCSRA,UDRE
+ rjmp CONTINUE
+ out UDR,r25
+ ldi r20,0
+ WAIT:
+ ldi r21,0
+ WAIT_II:
+ inc r21
+ cpi r21,0xff
+ brne WAIT_II
+ inc r20
+ cpi r20,0xff
+ brne WAIT
+
+ ldi r16,(1<<INT0) ; (re)activate int0
+ out GIMSK,r16
+