AVR Assembly program using adc, the multiplexer, and sram for variable data

lightLight.asm

;Night Light program from p.148
;
;example program using adc, mux, and sram variable storage
;
;compile with gavrasm serial_assembly.asm
;flash with avrdude -c avrisp -p m168 -P /dev/tty.usbmodem1411 -b 19200 -U flash:w:serial_assembly.hex
;
;program to utilize adc mux
.device atmega 168
        rjmp    start
.dseg
l_thresh: .byte 2
s_val: .byte 2
.cseg
.org 0
.def temp = r16
.def temp2 = r17
;--- Inits ---
;
start:  lds     temp,ADMUX
        ori     temp,(1 << REFS0)
        sts     ADMUX,temp
        lds     temp,ADCSRA
        ori     temp,(1 << ADPS1) | (1 << ADPS0) | (1 << ADEN)
        sts     ADCSRA,temp
        ldi     temp,0xff
        out     DDRB,temp
loop:   lds     temp,ADMUX
        andi    temp,0xf0
        ori     temp,3          ;pot sensor channel PC3 = 3
        sts     ADMUX,temp
        lds     temp,ADCSRA
        ori     temp,(1 << ADSC)        ;start adc
        sts     ADCSRA,temp
wait:   lds     temp,ADCSRA
        sbrc    temp,ADSC
        rjmp    wait
        lds     temp,ADCL
        ldi     r26,low(l_thresh)
        ldi     r27,high(l_thresh)      ;load X with address of l-thresh
        st      X+,temp
        lds     temp,ADCH
        st      X,temp
;read sensor value and store in s_val
        lds     temp,ADMUX
        andi    temp,0xf0
        ori     temp,0          ;light sensor PC0
        sts     ADMUX,temp
        sts     ADMUX,temp
        lds     temp,ADCSRA
        ori     temp,(1 << ADSC)
        sts     ADCSRA,temp
wait2:  lds     temp,ADCSRA
        sbrc    temp,ADSC
        rjmp    wait2
        lds     temp,ADCL
        ldi     r28,low(s_val)
        ldi     r29,high(s_val)
        st      Y+,temp
        lds     temp,ADCH
        st      Y,temp
;compare readings
        ld      temp,X          ;high byte of pot reading
        ld      temp2,Y         ;high byte of sensor reading
        cp      temp,temp2
        brge    setLed
        ld      temp,-X
        ld      temp2,-Y
        cp      temp,temp2      ;low pot compare low sensor
        brge    setLed
        ldi     temp,0x00
        out     PORTB,temp
        rjmp    loop
setLed: ldi     temp,0xff
        out     PORTB,temp
        rjmp    loop