* Main program to test memcopy subroutine.
* Assemble & step through this in THRSIM,
* watching the memory dump of region $0000, 
* and comparing it to the dump of $1000.

test:		LDD	#$40	; Copy 40 bytes
		LDX	#$1000	; from $1000 (control regs)
		LDY	#$0000	; to $0000 (internal RAM)
		BSR	memcopy	; Do it!
end:		BRA	end	; Stop here

* Copy one region of memory to another.
* Inputs:
*	X = Address of 1st byte of source region.
*	Y = Address of 1st byte of destination region.
*	D = Number of bytes to copy.

memcopy:	CPD	#0	; Compare D to 0.
		BEQ	done	; If D=0, nothing left to copy.
		PSHA		; Save the MSB of D.
		LDAA	0,X	; Load next byte to copy.
		INX		; Go to next source byte.
		STAA	0,Y	; Store A at destination addr.
		INY		; Go to next destination byte.
		PULA		; Restore the MSB of D.
		SUBD	#1	; Decrement # of bytes left.
		BRA	memcopy	; Repeat.
done:		RTS		; Return to caller.