**************************************************************************
* Parameter Declearation Section
*
* Export Symbols
            xdef        pgstart         ; export 'pgstart' symbol
            absentry    pgstart         ; for assembly entry point

* Symbols and Macros
PORTA       equ         $0000           ; i/o port A addresses
DDRA        equ         $0002           ; data direction register for PORTA
PORTB       equ         $0001           ; i/o port B addresses
DDRB        equ         $0003           ; data direction register for PORTB

**************************************************************************
* Data Section: address used [ $3000 to $30FF ] RAM Memory
*
            org         $3000           ; Reserved RAM memory starting address
                                        ;   for Data for CMPEN 472 class
SOURCE      ds.b        $000C           ; 12 Byte source array

LENSRC      dc.w        $000C           ; Length of the Source Array
                                        
DEST        ds.b        $000C           ; 12 Byte destination array

LENDST      dc.w        $000C           ; Length of the destination array

StackSP     dc.w        $3100           ; Address of the stack

*
**************************************************************************
* Program Section: address used [ $3100 to $3FFF ] RAM Memory
*
            org         $3100           ; Program start address, in RAM
pgstart     lds         StackSP         ; initialize the stack pointer
            ldaa        #1              ; Load 1 into A
            ldx         #SOURCE         ; Load the address of SOURCE into X
            ldy         LENSRC          ; Load the length of SOURCE into Y
fillLoop    tbeq        Y,doneLoop      ; If Y==0, jump to done loop
            staa        1,X+            ; Copy A into address of X, add 1 to X
            inca                        ; Increment A by 1
            dey                         ; Decrement Y by 1
            bra         fillLoop        ; Jump to fillLoop
doneLoop    jsr         memcpy          ; Call memcpy
            bra         done


**************************************************************************
* Subroutine Section: address used [ $3100 to $3FFF ] RAM Memory
*

;*************************************************************************
; memcpy subroutine
;
; This subroutine will copy LENSRC bytes from SOURCE to DEST.
;
; Input:                   Two addresses, SOURCE and DEST, 1 word length LENSRC
; Output:                  LENSRC bytes copied from SOURCE to DEST
; Registers in use:        D to count the number of bytes copied
;                          Y to hold the address of the current byte in SOURCE
;                          X to hold the address of the current byte in DEST
; Memory locations in use: One word, LENSRC, for the length of bytes to copy
;                          Two arrays, SOURCE & DEST, to copy from SOURCE to DEST
;
memcpy      
            pshy                        ; Save Y to the stack
            pshx                        ; Save X to the stack
            pshd                        ; Save D to the stack
            ldy         #SOURCE         ; Load the address of the source array into Y
            ldx         #DEST           ; Load the address of the destination array into X
            ldd         LENSRC          ; Load the length of the source array into D
loop        tbeq        D,EXIT          ; If d==0, jump to EXIT
            movb        Y,X             ; Copy data from address in Y to address in X
            inx                         ; Increment X by 1
            iny                         ; Increment Y by 1
            subd        #1              ; Decrement D by 1
            bra         loop            ; Branch always to loop
EXIT        puld                        ; Restore D from the stack
            pulx                        ; Restore X from the stack
            puly                        ; Restore Y from the stack
            rts                         ; Return to caller
            
*
**************************************************************************

done        
            end                         ; Last line of the file