AVR Interrupts. Assembly version of Elliot Williams helloInterrupts.c

helloInterrupt.asm

;Interrupt 0 Example
; Flashes LED0 at a fixed rate, interrupting whenever button is pressed
;
.device atmega 168 
.def temp = r16 
.def temp2 = r17 
.org 0
;
;Interrupt Vector Table
        jmp     reset
        jmp     chg_btn         ;int0
;Interrupt code overlaps the IVT b/c its not used
chg_btn:
        sbic    PIND,PD2
        rjmp    b_set
        cbi     PORTB,PB1
        reti
b_set:  sbi     PORTB,PB1
        reti
;Start of program
reset:
        ldi     temp,high(RAMEND)
        out     SPH,temp
        ldi     temp,low(RAMEND)
        out     SPL,temp                ;stack init required for interrupts
        sbi     EIMSK,INT0              ;enable int0
        lds     temp,EICRA
        sbr     temp,ISC00
        sts     EICRA,temp              ;set external interrupt control register to interrupt change
        sei                             ;set global interrupt
        sbi     PORTD,PD2               ;set pullup on button pin 
        ldi     temp,0xff
        out     DDRB,temp               ;set led's active
.equ d_cnt = 50000
loop:
        ldi     r24,low(d_cnt)
        ldi     r25,high(d_cnt)
delay:  sbiw    r25:r24,1
        brne    delay
        in      temp,PORTB
        ldi     temp2,0b00000001
        eor     temp,temp2
        out     PORTB,temp
        rjmp    loop