; Author: Jake Goodwin
; Date: 2023
; Description: An assembly file for an avr328 chip.

;Needed for uc info and defines
;This is in the /opt/microchip/mplabx/v6.05/packs/Microchip/ATmega_DFP/3.0.158/avrasm/inc/m328Pdef.inc
;.device m328p
.include "m328Pdef.inc"


;The device is setup with 1Mhz internal clock.

.def    mask    = r16   ; mask register
.def    ledR    = r17   ; led register
.def    loopCt  = r18   ; loop count register
.def    iloopRl = r24   ; inner loop register high.
.def    iloopRh = r25   ; inner loop register low.

;.equ    iVal    = 39998 ; inner loop value
.equ    iVal    = 10000 ; inner loop value

.cseg
;.org 0x0000
.org 0x00
        ldi     r16, LOW(RAMEND)    ;init
        out     SPL, r16            ;stack pointer
        ldi     r16, HIGH(RAMEND)   ;to ramend
        out     SPH, r16            ; "
        
        ;setup the led
        clr     ledR                ;clear led register
        ;ldi     mask,(1<<PIND0)     ;load 00000001 into register.
        ldi     mask, 255
        out     DDRD, mask          ;set pinD0 to output.
        
        
        ldi     r30, 0x1
        sts     0x200, r30

        ;ldi     ledR, 1
        ;jmp     start
        ;jmp     ledchaser
        jmp     check_address

;checks to see if an address in RAM location 0x200 contains value 0.
check_address:
    .equ    myloc   =0x200
    
        lds     r30, myloc          ;loads data from ram into register 30
        tst     r30                 ;sets flags basedo n r30

        brne    ledchaser           ;branch if r30 isn't zero.
        
        
        sbi     DDRD, 1             ;set led pin for output.
        sbi     PORTD, 1            ;turn on the led pin.
        
        done:   jmp     done

ledchaser: 
        out     PORTD, ledR         ;write led register to portd
        
        lsl     ledR
        ldi     loopCt,25
        rcall   delay10ms

        tst     ledR
        brne    ledchaser

        ldi     ledR, 1
        rjmp    ledchaser
       

start:	eor	ledR,mask		    ; toggle PIND0 in led register

        ;indicate it's in start.
        sbi     DDRD, 1
        sbi     PORTD, 1 

        out	PORTD,ledR		        ; write led register to PORTD

        ;ldi	loopCt,50		        ; initialize delay multiple for 0.5 sec
        ldi	    loopCt,25		        ; initialize delay multiple for 0.5 sec
        rcall	delay10ms		    ; call delay subroutine

        rjmp	start			    ; jump back to start

delay10ms:
        ldi     iloopRl, LOW(iVal)      ;initialize inner loop registers
        ldi     iloopRh, HIGH(iVal)     ;high and low.

;sbiw, subtract imediate from word.
iLoop:  sbiw iLoopRl, 1          ; decrement inner loop register.
        brne    iLoop               ;branch to iLoop if iLoop register zero.

        dec     loopCt              ;decrement outer loop reg
        brne    delay10ms           ;branch to oloop is zero.

        nop                         ;no operation, do nothing.
        ret                         ;return from subroutine.