; ***********************************************************************
; *									*
; *          Flash the LEDs on the DSLMU Microcontroller Board          *
; *                            First Version                            *
; *									*
; ***********************************************************************
;
; Author:   John Zaitseff <J.Zaitseff@unsw.edu.au>
; Date:     24th June, 2003
; Version:  1.8
;
; This program, when run on the DSLMU Microcontroller Board, flashes the
; LEDs on and off.  Apart from some of the comments, it is essentially
; identical to flash-v1.s in Experiment 1.


; -----------------------------------------------------------------------
; Constant values used in this program

	.equ	portA,  0x10000000	; Address of Port A in the I/O space

	.equ	Value1, 0b11111111	; Value to turn LEDs on
	.equ	Value2, 0b00000000	; Value to turn LEDs off


; -----------------------------------------------------------------------
; Assembly-language preamble

	.text				; Executable code follows

_start:	.global	_start			; "_start" is required by the linker
	.global	main			; "main" is our main program

	b	main

; -----------------------------------------------------------------------
; Start of the main program

main:					; Entry to the function "main"

	; Although "main" is technically a function, this particular
	; function has an infinite loop and so never returns to its caller.

	ldr	r1, =portA		; Load address of Port A into R1
					; (ie, the value of the constant
					; LED_port) into register R1

main_loop:				; Start of the infinite loop

	mov	r0, #Value1		; Load value to turn LEDs on
	strb	r0, [r1]		; Write the byte to Port A

	mov	r0, #Value2		; Load value to turn LEDs off
	strb	r0, [r1]		; Write the byte to Port A

	b	main_loop		; Do this forever (or until stopped)

; -----------------------------------------------------------------------

	.end