blink.asm

.device ATmega328P

.org 0x0000
	jmp reset

; mem loc for interript 0
.org 0x0002
	jmp button_pushed

button_pushed:
	cbi PINB, PINB5 ; disable LED
	reti

reset:
	sbi DDRB, PINB5 ; set LED to output

	; initialize the stack
	ldi r16, LOW(RAMEND)
	out SPL, r16
	ldi r16, HIGH(RAMEND)
	out SPH, r16

	; initalize the EICRA (external interrupt control register)
	lds r17, EICRA
	ori r17, 0b00000010
	sts EICRA, r17

	; enable pin 2
	in r18, EIMSK
	ori r18, 0b00000001
	out EIMSK, r18

	sbi PINB, PINB5 ; enable LED
	sei ; enable interrupt handler

; loop forever, all logic is done in interrupt handler
main:
	rjmp main