;
; This simple program uses interrupts and targets the atmega328P. It configures
; and enables both Int0 and Int1.  The sense of both interrupts is configured
; to be rising-edge.  Be sure to consult the ATmega328P reference for details.
;


;
; Some equates to associate names with numbers
;
.equ _spl =   0x5d
.equ _ddrd =  0x2a
.equ _portd = 0x2b
.equ _mcucr = 0x55
.equ _eimsk = 0x3d
.equ _eicra = 0x69

rjmp entry
nop
rjmp isr_0
nop
rjmp isr_1
nop

.org 0x60
isr_0:
    add r17,r1
    reti

.org 0x70
isr_1:
    add r18,r1
    reti

.org 0x80 ; was 0x74, 0xc8 bumps up against 0x100 threshold.
entry:
    com r1
    neg r1        ; r1 = 1
    ldi r16,0
    ldi r17,0
    ldi r18,0

    call InitInt0
    call InitInt1

    ; mdw: do this manually in the simulator
    ; sei ; enable interrupts

sink:
    add r16,r1
    rjmp sink

InitInt0:
    push r24

    lds r24,_ddrd ; load DDRD
    andi r24,0xfb  ; clear PD2 pin
    sts _ddrd,r24 ; write back to DDRD

    lds r24,_portd ; load PORTD
    ori r24,0x04    ; enable pullup for PORTD[2]
    sts _portd,r24 ; write back to PORTD

    ; this sets int0 to trigger on rising edge...
    lds r24,_eicra ; load EICRA
    ori r24,0x03    ; enable isc00,isc01
    sts _eicra,r24 ; write back to EICRA

    lds r24,_eimsk ; load EIMSK
    ori r24,0x01    ; enable INT0 in EIMSK
    sts _eimsk,r24 ; write back to EIMSK

    pop r24
    ret

InitInt1:
    push r24

    lds r24,_ddrd ; load DDRD
    andi r24,0xf7  ; clear PD3 pin
    sts _ddrd,r24 ; write back to DDRD

    lds r24,_portd ; load PORTD
    ori r24,0x08    ; enable pullup for PORTD[3]
    sts _portd,r24 ; write back to PORTD

    ; this sets int0 to trigger on rising edge...
    lds r24,_eicra ; load EICRA
    ori r24,0x0c    ; enable isc10,isc11
    sts _eicra,r24 ; write back to EICRA

    lds r24,_eimsk ; load EIMSK
    ori r24,0x02   ; enable INT1 in EIMSK
    sts _eimsk,r24 ; write back to EIMSK

    pop r24
    ret