; CE-2800 Watchdog timer demo
; Purpose: Demonstrates the operation/setup/configuration of the Watchdog timer.

.NOLIST
.INCLUDE "m32def.inc"		; contains .EQU's for DDRB, PORTB, and a lot more
.LIST

.DSEG
ADFlag:	.byte 1				; 1-byte flag used to indicate whether PA0 or PA1 is being measured

.EQU start = 0x2a			; define a symbol to represent address 0x2a in program memory
.CSEG						; this means further directives are for the Code Segment
.ORG 0x0
	rjmp 	start			; initialize Reset Vector at 0x0000
.ORG 0x2
	rjmp	int0_ISR		; initialize INT0 Vector at 0x0002
.ORG 0x4
	rjmp	int1_ISR		; initialize INT1 Vector at 0x0004

.CSEG					; switch back to Code Segment
.ORG start				; defines where these instructions start getting placed in Program Memory

; Initialize the Stack Pointer (SP) CPU register for subsequent use
.DEF temp=r21			; temp: register for temporary data store

	ldi	    temp, LOW(RAMEND)	; get low byte of the address of the highest byte in Data Memory we can use
	out	    SPL, temp			; load it into the low byte of SP
	ldi	    temp, HIGH(RAMEND)	; high byte of address of highest Data Memory byte
	out	    SPH, temp			; load it into the high byte of SP

	rcall	initPortB
	rcall	initPortD
	rcall	initExternalInterrupts


	sei							; this ENABLES interrupts globally

	rcall	doStartFlash		; flash the LEDs to signal start of program execution

	ldi		R16, 0x01		; set rightmost bit
repeat_left:
    out     PORTB, R16
	rcall	delay60
	lsl		R16				; shift bits left
	brcc	repeat_left		; and repeat if bit hasn't been rolled into Carry
	sbr		R16, 0x40		; otherwise reset bit 6

repeat_right:
    out     PORTB, R16
	rcall	delay60
	lsr		R16				; shift bits right
	brne	repeat_right	; and repeat if bit hasn't been rolled into Carry
	sbr		R16, 0x02	; otherwise reset bit 1
	rjmp	repeat_left		; and start shifting left again

loop_forever:
	rjmp loop_forever


; subroutine doStartFlash
; flashes the LED's 5 times with a delay of 100ms between each flash
doStartFlash:
	push 	temp			; save incoming value of temp
	ldi		temp, 5			; use temp as a counter; initialized to 5
repeat_flash:
	push	temp			; save the value of the count

	ldi		temp, 0xff		
	out		PORTB, temp		; turn LEDs on
	rcall	delay100
	ldi		temp, 0
	out		PORTB, temp		; turn LEDs off
	rcall	delay100
	pop		temp			; restore the value of the count
	dec		temp			; decrement the count
	brne	repeat_flash	; if not 0, repeat

	pop		temp			; restore incoming value of temp
	ret
; end subroutine doStartFlash

; subroutine initPortB
; configure PORTB for digital output
initPortB:
	push	temp
	ldi	    temp, 0xff  	; set all bits to 1
	out     DDRB, temp		; tell DDRB to configure pins as output (0xff means all output)
	ldi	    temp, 0xff
	out	    PORTB, temp
	pop		temp
	ret
; end subroutine initPortB

; subroutine initPortD
; configure PORTD for digital input
initPortD:
	push	temp
	ldi		temp, 0x00	  		; init PortD for digital INPUT
	out 	DDRD, temp			
	ldi		temp, 0xff	  		; enable pull-up circuitry
	out		PORTD, temp
	pop		temp
	ret			
; end subroutine initPortD


; subroutine setupIninitExternalInterruptsterrupts
; enable global interrupt handling, and initilize interrupt handling specifically for INT0
initExternalInterrupts:
	push	temp				; save

	in		temp, GICR			; get current state of GICR (General Interrupt Control Register)
	ori		temp, 1<<INT0			; bits in GICR enables external interrupt 0
	ori		temp, 1<<INT1			; bits in GICR enables external interrupt 1
	out		GICR, temp			; set the bits

  ; MCUCR - MCU Control Register
	in		temp, MCUCR			; get current state of MCUCR
	ori		temp, 1<<ISC01			; these bits in MCUCR define interrupts to occur on fall of signal on INT0 pin
	sbr		temp, 1<<ISC11			; these bits in MCUCR define interrupts to occur on fall of signal on INT1 pin
	out		MCUCR, temp			; set the bits

	pop		temp				; restore
	ret
; end subroutine initExternalInterrupts


; interrupt handler int0_ISR
; Purpose: implements the handling of the int0 external interrupt
int0_ISR:
	push	temp

	ldi		temp, 0x0f
	out		PORTB, temp
	rcall	delay60

	pop		temp
	reti
; end interrupt handler int0_ISR

; interrupt handler int1_ISR
; Purpose: implements the handling of the int1 external interrupt
int1_ISR:
	push	temp

	ldi		temp, 0xf0
	out		PORTB, temp
	rcall	delay60

	pop		temp
	reti
; end interrupt handler int1_ISR

.include "delay.asm"