;Eric Melin and Brian Glassmeyer
;;********************************************
;;*** Final Project: Counter Test
;;*** With pushbuttons and LED display.
;;********************************************

;Port A Counter Bits (1-8)
;Port B Controls the LEDs
;Port C Out to Counter/Counter Bits (9-12)
;Port D Button Inputs

.include	"8535def.inc"
.device AT90S8535

.def	savSREG	=r1	;save the status register
.def	cntlow	=r16	;the lower byte of captured counter 
.def	cnthigh	=r17	;the upper 4 bits of captured counter 
.def	cntinc	=r18	;clock to increment counter
.def	temp	=r19	;temporary register
.def	running	=r20	;0(running)/1(stopped)
.def	display	=r21	;0(low byte)/1(high bits)

.equ	pb_start_stop	=1	;button to toggle start/stop
.equ	pb_clear	=2	;button for clearing the counter
.equ	pb_display	=4	;button to toggle low/high bits displayed
.equ	Prescale0	=0x05	;clk/1024
.equ 	Prescale1	=0x0C	;clk/256
.equ	cntclear	=0x80	;mask for clr signal to counter
.equ	cntincbit	=0x40	;mask for clk_ signal to counter
.equ	cnthighmask	=0x07	;mask for incoming high bits from counter

;**************************************
.dseg

;**************************************
.cseg

.org $0000
	rjmp 	RESET	;reset entry vector
	reti		
	reti
     	reti
	reti
	reti
	rjmp    T1compA
	reti
	reti ;rjmp	T1ovfl	;Increment counter & update LEDs
	rjmp    T0ovfl	;Check button press
	reti		
	reti	
	reti	
	reti 	
	reti
	reti
	reti

RESET:	ldi   	temp, LOW(RAMEND)   ;setup stack pointer
	out   	SPL, temp
	ldi   	temp, HIGH(RAMEND)
	out   	SPH, temp
	
	;start clock
	ldi	display, 0
	ldi	running, 1
	ldi	temp, Prescale0
	out	TCCR0, temp
	;do a compare match
	ldi 	temp, 0x00
	out	OCR1AH, temp
	ldi	temp,0xf0 	
	out 	OCR1AL, temp
	ldi	temp, Prescale1
	out	TCCR1B, temp
	ldi	temp,0b00010001	;Enable Timer0 and Timer1 interrupts
	out	TIMSK,temp 

	;init port directions
	ldi	temp, 0x00
	out	DDRD, temp
	out	PORTD, temp
	out	DDRA, temp
	out 	PORTA, temp
	ldi	temp, 0xFF
	out	DDRB, temp	;Set PORTB as LED outputs
	;out	PORTB, temp	;Initially turn off LEDs
	ldi	temp, 0xE0
	out	DDRC, temp	;Set PORTC(5-7) as counter outputs

     	sei

SPIN:	rjmp	SPIN		;interrupt driven test

;******************************************************
;********Interrupt Routines

;Checks for button press
T0ovfl:	in	savSREG, SREG		;Determine which button
	sbic	PORTD, pb_start_stop
	rjmp	start_stop
	sbic	PORTD, pb_clear
	rjmp	clear
	sbic	PORTD, pb_display
	rjmp	high_low
	out	SREG, savSREG		;No button was pressed
	reti

start_stop:
	tst	running		;Check current running status
	brne	stop
	ser	running		;Was stopped--now run counter
	out	SREG, savSREG
	reti
stop:	clr	running		;Was running--now stop counter
	out	SREG, savSREG
	reti

clear:
	ldi	temp, cntclear	;set clear signal to counter
	out	PORTC, temp
	clr	temp		;remove clear signal
	or	temp, cntinc	;  but don't mess the clk_ signal
	out	PORTC, temp
	out	SREG, savSREG
	reti

high_low:
	tst	display		;Check current display status
	brne	low
	ser	display		;Change to high bits
	out	SREG, savSREG
	reti
low:	clr	display		;Change to low bits
	out	SREG, savSREG
	reti


;Increment counter & update LED display
T1compA:	in	savSREG, SREG
	tst	running
	breq	done
	com	cntinc			;Toggle for clk_ signal
	andi	cntinc, cntincbit	;mask for the clk_ signal
	out	PORTC, cntinc
	ldi	cntlow, 0xf0
	in	cntlow, PINA		;Capture low byte of counter
	com	cntlow			; convert for active low LEDs
	;ldi	cntlow, 0x04
	;out	PORTB, cntlow		;Display low byte
	in	cnthigh, PINC		;Capture high 5 bits of counter
	andi	cnthigh, cnthighmask	; mask just the 4 bits
	com	cnthigh			; convert for active low LEDs
	tst	display
	brne	disphigh
	out	PORTB, cntlow		;Display low byte
	rjmp	done
disphigh:
	;out	PORTB, cnthigh		;Display high bits

done:	out	SREG, savSREG
	reti