; lightSensor.asm
;
;  Ryan Castonia
;  December 2009
;
;  light sensor code for weightlifting power meter.  See http://fab.cba.mit.edu/classes/MIT/863.09/people/ryan/index.htm


.include "tn44def.inc"
;
; definitions
;
.equ commPin = PA0
.equ LEDPin = PB2
.equ checkValue = 750
;
; registers
;
.def bitcnt = R16; bit counter
.def temp = R17; temporary storage
.def temp1 = R18; temporary storage
.def txbyte = R19; data byte
.def ADOutput = R20
.def velocity = R21
.def flag = R22
.def previous = R23

;
; code segment
;
.cseg
.org 0
rjmp reset

;counter/timer output compare A interrupt
.org 6

; compare current velocity count with previous value
mov temp, velocity
mov temp1, previous
cpc temp, temp1
; if the current value is lower, print the previous value
brlo print

; otherwise, move the current value into the previous value
mov previous, velocity
clr velocity
sei
rjmp main_loop

print:
; send the highest velocity count recieved during the lift
   mov txbyte, previous
   rcall putchar
   clr velocity
   clr previous

 sei
 rjmp main_loop

;
; half_bit_delay
; serial half bit delay
;
half_bit_delay:
   ldi temp, 100
   half_bit_delay_loop:
      dec temp
      brne half_bit_delay_loop
   ret
;
; putchar
; assumes no line driver (doesn't invert bits)
;
putchar:
   ldi bitcnt, 10; 1 start + 8 data + 1 stop bit
   com txbyte; invert everything
   sec; set start bit
   putchar0:
      brcc putchar1; if carry set
      sbi PORTA, commpin; send a '0'
      rjmp putchar2; else	
   putchar1:
       cbi PORTA, commpin	; send a '1'
       nop; even out timing
   putchar2:
       rcall half_bit_delay; bit delay
       rcall half_bit_delay; " 
       lsr txbyte; get next bit
       dec bitcnt; if not all bits sent
       brne putchar0; send next bit
   ret;
;
; main program
;
reset:
   
   ;
   ; set stack pointer to top of RAM
   ;
   ldi temp, high(RAMEND)
   out SPH, temp
   ldi temp, low(RAMEND)
   out SPL, temp
   ;
   ; init comm pin and LED pin for output
   ;
   sbi PORTA, commPin
   sbi DDRA, commPin
   sbi PORTB, LEDPin
   sbi DDRB, LEDPin

   ;
   ; init A/D for the sensor pin
   ;
   cbi ADMUX, REFS1 ; use Vcc as reference
   cbi ADMUX, REFS0 ; "
   cbi ADMUX, ADLAR ; right-adjust result
   cbi ADMUX, MUX5 ; set MUX to ADC7 (PA7)
   cbi ADMUX, MUX4 ; "
   cbi ADMUX, MUX3 ; "
   sbi ADMUX, MUX2 ; "
   sbi ADMUX, MUX1 ; "
   sbi ADMUX, MUX0 ; "
   sbi ADCSRA, ADEN ; enable A/D
   cbi ADCSRA, ADPS2 ; set prescaler to /2
   cbi ADCSRA, ADPS1 ; "
   cbi ADCSRA, ADPS0 ; "
      
	  ; allow timer/counter interrupt
    sei
	ldi temp, (1 << OCIE1A) ; output compare A
	out TIMSK1, temp
 
  ; set up 16bit counter1 with clock/64 and CTC
   ldi temp1, (1 << WGM12) | (0 << CS12) | (1 << CS11) | (1 << CS10)
   out TCCR1B, temp1
 
   ; set Output Compare Register A value (1/4 sec)
   ldi temp, 16
   ldi temp1, 0
   out OCR1AH, temp
   out OCR1AL, temp1

   sbi PORTB, LEDPin
   ldi previous, 0

   ;
   ; start main loop
   ;
   
main_loop:
      sbi ADCSRA, ADSC ; start conversion
	  AD_loop:
         sbic ADCSRA, ADSC ; loop until complete
	     rjmp AD_loop
      rcall update
      rjmp main_loop

update:
	in ADOutput, ADCL ; low byte
	in ADOutput, ADCH ; hi byte
	ldi temp, high(checkValue)
	cpc temp, ADOutput
	brsh lightOn
	rjmp lightOff

; these methods make sure that the rotary encoder properly counts the teeth

lightOn:
ldi flag, 0
rjmp main_loop

lightOff:
sbrs flag, 0
rjmp up
rjmp main_loop

up:
inc velocity
ldi flag, 1
rjmp main_loop