assembly version of cylon eyes from Elliot Williams AVR Programming

cylonEyes.asm

;assembly version of Cylon Eyes p.60
;compile with gavrasm cylonEyes.asm
;
;--- set up ---
.device atmega168
.cseg
.org 0
.def delayH     =r25
.def delayL     =r24
.def led        =r16
.def temp       =r17
.equ dlp_init   =2500   ; 2500 * 4 clock cycles = 10,000u = 100ms
;--- inits ---
        ldi     temp,0xff
        out     DDRB,temp
; need to setup stack
        ldi     temp,low(RAMEND)
        out     SPL,temp
        ldi     temp,high(RAMEND)
        out     SPH,temp
;--- main loop
lp:
        ldi     led,0x01
l_lp:
        out     PORTB,led
        rcall   delay
        lsl     led     ;shift bits left until led == 0
        brne    l_lp
        ldi     led,0x80        ;0b1000000
r_lp:
        out     PORTB,led
        rcall   delay
        lsr     led
        brne    r_lp
        rjmp    lp
;--- delay subroutine
delay:
        ldi     delayH,high(dlp_init)
        ldi     delayL,low(dlp_init)
dlp:    sbiw    delayH:delayL,1
        brne    dlp
        ret