; led_sw3.s :Testing GPIO_0 for input/output to be run on the LPC2131 board 
;(ver. 2012 onward)
;
;Exercise1 : run this program, you should see:
;   When you press the button (sw3), the LED(D1) is on, otherwise LED(D1) is off.
;	Try to understand the function of every statement of this program
;
;Exercise2: Modified the program so your output is reversed:
;   When you press the button (sw3), the LED(D1) is off, otherwise LED(D1) is on.
;
;Exercise3: Modified the program, so you you can use sw4 (P0.11) to control LED D2 (P0.21)
;			as in exercise 1.
;Exercise4: Modified the program, so when you press sw3 once , 
;           the LED(D1) will toggle (change state from on_to_off or off_to_on)
;
; Note: LED(D1) is at GPIO P0.10, sw3 is at GPIO P0.20	(also for EINT3 external interrupt input) 
; Note: LED(D2) is at GPIO P0.11, sw4 is at GPIO P0.21
; Note: LED(D3) is at GPIO P0.12, sw5 is at GPIO P0.22
; Note: LED(D4) is at GPIO P0.13, sw6 is at GPIO P0.23
		AREA    |.data|, DATA, READWRITE
IO0DIR	EQU	0xE0028008	; pin direction
IO0SET	EQU	0xE0028004	; pin value set
IO0CLR	EQU	0xE002800C	; pin value clear
IO0PIN	EQU	0xE0028000	; pin value read & write
RED_LED  EQU 0x00000400;   0100,0000,0000B p0.10=RED LED
SW3 	 EQU 0x00100000;   0001,0000,0000,0000,0000,0000B,p0.20 is SW3
       AREA    |.text|, CODE, READONLY; User Initial Stack & Heap
        EXPORT  __main
__main	; set p0.22(red led) as output using the IO0DIR register
		LDR 	R1, =RED_LED
     	LDR 	R0, =IO0DIR
     	STR 	R1,[R0];
loop 	LDR 	R3, =IO0PIN; target at the IO0PIN register
     	LDR  	R3, [R3]; load IO0PIN value to R3 register	 
		; if the switch is depressed, corresponding pin value is 0
    	TST  	R3, #SW3;test on pin 20 of IO0PIN to see if SW3 is depressed
    	BEQ  	onled ;if IO0PIN[20]=0, go to onled to light the led
		;otherwise LEDoff
offled  LDR 	R1, =RED_LED
  		LDR 	R0, =IO0CLR
  		STR 	R1,[R0]
       	B loop
      ;------ON LED---------
	  ; write 1 in the 22nd bits of IO0SET to turn on the LED
onled   LDR 	R1, =RED_LED
    	LDR 	R0, =IO0SET
    	STR 	R1,[R0]
    	B loop 
   END