light metering program in avr assembly

lightMeter.asm

;Light Meter assembly version
;based on E.Williams AVR Programming lightSensor.c p.135
;compile with gavrasm lightMeter.asm
;
.device atmega 168 
.cseg
.org 0
.def temp = r16 
;--- Inits ---
        ldi     temp,0xff
        out     DDRB,temp       ;output on led ports
        lds     temp,ADMUX
        ori     temp,(1 << REFS0) | (1 << ADLAR)        ;reference voltage on AVCC. Use Left Justified data
        sts     ADMUX,temp
        lds     temp,ADCSRA
        ori     temp,(1 << ADPS1) | (1 << ADPS0) | (1 << ADEN)
;Enables ADC and set clock prescaler to 8
        sts     ADCSRA,temp
;--- event loop ---
lp:
        lds     temp,ADCSRA
        ori     temp,(1 << ADSC)
        sts     ADCSRA,temp     ;start ADC conversion
wait:   lds     temp,ADCSRA
        sbrc    temp,ADSC       ;wait for ADSC bit to clear
        rjmp    wait
.def adH = r17 
.def s_adc = r18 
; get converted data and right shift four
        ldi     temp,1
        out     PORTB,temp      ;got through first wait * debugging
        lds     s_adc,ADCH
        lsr     s_adc
        lsr     s_adc
        lsr     s_adc
        lsr     s_adc
.undef adH 
.def count = r17 
        ldi     temp,2
        out     PORTB,temp      ;got through second stage * debugging
        mov     count,s_adc
        ldi     temp,1
l_lp:   out     PORTB,temp
        sec 
        rol     temp
        dec     count
        brne    l_lp
;delay
.equ d_cnt = 50000
        ldi     r25,high(d_cnt)
        ldi     r24,low(d_cnt)
dlp:    sbiw    r25:r24,1
        brne    dlp
        rjmp    lp

The hard part of this program was figuring out ADCH bytes aren't updated until ADCHL is read. So in order to do the bit shift I had to left justify the ADC value (ADLAR = 1).