AVR ASM First Steps

Hey Gang,

I finally got some time to get my AVR ASM tool chain up and running on Mac OSX. I'm posting my first hand written ASM code for making an LED blink, using a Mega8 (PD4, aka pin 6 on the meaga8). Let me know if you have any questions about getting your toolchain up and running. It is a bit of work to get it all set up, but it can be very satisfying to see your first program run on a $2 computer!

.include "m8def.inc" 

.def temp       = r16
.def delay1     = r17
.def delay2     = r18
.def delayv     = r19
.equ led        = 4                     ; PORTD bit number to blink LED on

.org 0x0000                             ; the next instruction will be written to 0x0000
rjmp main                               ; jump to main:

delay:
        clr     delay1                  ; set delay1 to 0
        clr     delay2                  ; set delay2 to 0
        ldi     delayv, 10              ; set delayv to 50
 
delay_loop:
        dec     delay2                  ; decrement delay2, if 0, dec will set delay2 back to 255
        brne    delay_loop              ; delay_loop: again if delay2 is not 0
        dec     delay1                  ; decrament delay1, if 0, dec will set delay1 back to 255
        brne    delay_loop              ; delay_loop: again if delay1 is not 0
        dec     delayv                  ; decrament delayv
        brne    delay_loop              ; delay_loop: again if delayv is not 0
        ret                             ; go back to where we came from

main:
        ldi     temp, low(RAMEND)       ; initiate the stack in the build in SRAM. Stack operations 
        out     SPL, temp               ; are always necessary when subroutines or interrupts are called.
        ldi     temp, high(RAMEND)      ; By calling the subroutine or interrupt handling routine the actual adress 
        out     SPH, temp               ; is written to the stack in order to later jump back to the code where the 
                                        ; interrupt or call occurred.

        sbi     DDRD, led               ; connect PORTD pin 4 to LED

loop:
        cbi     PORTD, led              ; turn PD4 high
        rcall   delay                   ; delay for an short bit
        sbi     PORTD, led              ; turn PD4 low 
        rcall   delay                   ; delay again for a short bit
        rjmp    loop                    ; recurse back to the start of loop:

Many thanks to leon, theusch, and srinivasandelta over at AVR Freaks for helping me get started.

cheers!