;***** AtoD Test with interrupt driven timing ********
;Timer 1 match function is used to take 1 sample/sec
; and display the top 8 bits on the LEDs.

;You will need to CHANGE this path
.include "8535def.inc"

.device AT90S8535 ; specifies to the assembler which chip we are using

.def	save	=r1	;SREG temp reg
.def	temp	=r16	;temporary register
.def	AnaLo	=r17	;A to D result
.def	AnaHi	=r18	;
.def	itemp	=r19	;temp reg for interrupts

;***** Initialization
.cseg
.org $0000
	rjmp 	RESET	;reset entry vector
	reti		
	reti
	reti
	reti
	reti	
	rjmp	t1match
	reti
	reti
	reti
	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

	;set up port B to run LEDS
	ser	temp		;set PORTD to be
	out	DDRD,temp	;all outputs to LEDs
	out	PORTD, temp

	;set up Timer 1 to interrupt on compare A match
	;and set the compare time to 62500 ticks
	ldi	temp,0b00010000	;enable t1 matchA interrupt
	out	TIMSK, temp
	ldi	temp, 0x00	;set the match A register to
	out	OCR1AH, temp	;83 since 83*2us=166us=1/6000
	ldi	temp, 83	;62500 = 0xf424
	out	OCR1AL, temp
	ldi 	temp,0b00001010	;prescale timer by 8 (one tick=16 microsec)
	out 	TCCR1B, temp	;and clear-on-matchA

	;set up analog converter to read channel zero
	ldi	temp, 7
	out	ADMUX, temp
	
	sei	;enable all interrupts	

swait:	in	temp, ADCSR	;wait for A to D start
	andi	temp, 0b01000000;by checking if ADSC bit is set
	breq	swait		;this bit is set by t1match interrupt

await:	in	temp, ADCSR	;wait for A to D done
	andi	temp, 0b01000000;by checking ADSC bit
	brne	await		;this bit is cleared by the AtoD hardware
	
	in	AnaLo, ADCL	;read the voltage
	in	AnaHi, ADCH
	lsr	AnaHi		;double precision shift
	ror	AnaLo		;right twice
	lsr	AnaHi
	ror	AnaLo
	
	com	AnaLo		;invert for LEDs
	out	PORTD, AnaLo	;output the top 8 bits

	rjmp	swait

;**** timer 1 compare A match 1/sec

t1match:in	save, SREG

	ldi	itemp, 0b11000101	;start A to D conversion
	out	ADCSR, itemp

	out	SREG, save
	reti