init_code.s

@Code to turn on and off LEDs in a sequence, with 1 second delay between each LED switching.
@Program uses GPIO 21-24 LEDS in GPIO1 Mode. The logic to set outputs was calculated and the
@values to set and clear the registers were also found. More details at the end of the program.
@Program sets output values, then uses an array to set and clear the values for each LED.
@Branches and comparisons are used to pause the sequence of the LEDs then start the sequence where it was paused on
@the next button push.
@Ria Mahajan November 29. 2023

.text
.global _start1
.global INT_DIRECTOR
_start1:
		
		LDR R13,= STACK1		@POINT TO BASE OF STACK FOR SVC MODE
		ADD R13, R13, #0x1000	@POINT TO TOP OF STACK
		CPS #0x12				@SWITCH TO IRQ MODE
		LDR R13,=STACK2			@POINT TO IRQ STACK
		ADD R13, R13, #0x1000	@POINT TO TOP OF STACK
		CPS #0x13				@BACK TO SVC MODE

@INITIALIZE/TURN ON GPIO1
		MOV R0,#0x02
		LDR R1,=0x44E000AC		@BASE ADDRESS OF GPIO1
     	STR R0,[R1]				@TURN ON MODE1 (GPIO1)
     	LDR R0,=0x4804C000		@BASE ADDRESS OF GPIO1
     	ADD R4,R0,#0x190		@CLR_DATA REG LOAD VALUE
     	
     	
    	MOV R7, #0x00200000		@GPIO_22 TO HIGH WHEN OUPUT		(OUT 22 = 0100 = 4)
     	STR R7,[R4]				@WRITE TO GPIO_OE
     	
     	@GPIO AS OUPUT
        ADD R1,R0,#0x0134       @ADDRESS OF GPIO1_OE
        LDR R6,[R1]				@READ GPIO_OE
        LDR R7,=0xFE1FFFFF		@SET 21-24 TO OUTPUTS
        AND R6,R7,R6			@CLEAR BIT
        STR R6,[R1]				@WRITE TO GPIO_OE REG
        
        @FALLING EDGE
        ADD R1,R0, #0x14C		@FALLING EDGE DETECT
        MOV R2, #0x40000000		@LOAD VALUE FOR BIT 30 (BUTTON = GPIO1_30)
        LDR R3,[R1]				@READ FALLING DETECT REG
        ORR R3, R3, R2			@MODIFY
        STR R3,[R1]				@WRITE BACK
        ADD R1, R0, #0x34		@ADDRESS OF GPIO_IRQSTATUS_SET_0 REG
        STR R2,[R1]				@ENABLE GPIO1_30
        
        @INITIALIZE INTC
        LDR R1,=0x482000E8		
        MOV R2, #0x04			@UNMASK INTC INT 98, GPIOINT1A (PG280/282)
        STR R2,[R1]
       @POOL
       MRS R3, CPSR
       BIC R3, #0x80
       MSR CPSR_c, R3

       LOOP: NOP
     		 B LOOP       
 INT_DIRECTOR:
 			STMFD SP!,{R0-R5,LR}		@PUSH REGISTERS ON STACK
 			
 			LDR R0,=0x482000F8			@INT_PENDING_IRQ3 REG
 			LDR R1,[R0]					@INTC REG READ	
 			TST R1, #0x00000004			@TEST BIT 2
 			BEQ PASS_ON					@NOT FROM GPIOINTA, GO TO WAIT LOOP
 			LDR R0,=0x4804C02C			@LOAD GPIO1_IRQSTATUS_0 REG ADDRESS
 			LDR R1, [R0]				@READ STATUS REG
 TEST:		TST R1,#0x40000000			@CHECK IF BIT 30=1
 			BNE LED_CHECK					@IF YES, BUTTON PUSHED, GO TO BUTTON PROCEDURE
 			BEQ PASS_ON					@ELSE GO TO WAIT LOOP
LED_CHECK:	LDR R1,= 0x4804C000			@LOAD BASE ADDRESS OF GPIO1
		LDR R2,[R1,#0x013C]				@LOAD DATAOUT GPIO ADDRESS
		CMP R2, #0x00000000				@CHECK IF LED = 0
		BNE TEST3					@IF NO, GO TO TEST3
		B BUTTON
		
 			
 PASS_ON: 
       	  LDMFD SP!, {R0-R5,LR}
 		  SUBS PC,LR,#4
 		  
TEST3:
		MOV R1, #0x40000000				@VALUE TO TURN OFF GPIO1_30 REQ
			STR R1,[R0]					@WRITE TO GPIO1_IRQSTATUS_0
			
			@TURN OFF NEWIRQA BIT IN INTC_CONTROL
			LDR R0,=0x48200048			@ADDRESS OF INTC_CONTROL REG
			MOV R1, #01					@VALUE TO CLEAR BIT 0
			STR R1,[R0]					@WRITE TO INTC_CONTROL REG
LOOP2:			LDR R0,=0x4804C02C			@LOAD GPIO1_IRQSTATUS_0 REG ADDRESS
 			LDR R1, [R0]				@READ STATUS REG
			TST R1,#0x40000000			@CHECK IF BIT 30=1
			BLNE BUTTON 				@IF YES, BUTTON PUSHED, GO TO BUTTON PROCEDURE
 	  		BEQ LOOP2					@ELSE, GO TO LOOP2
 	  		 
 	  		
BUTTON:
		MOV R1, #0x40000000				@VALUE TO TURN OFF GPIO1_30 REQ
			STR R1,[R0]					@WRITE TO GPIO1_IRQSTATUS_0
			
			@TURN OFF NEWIRQA BIT IN INTC_CONTROL
			LDR R0,=0x48200048			@ADDRESS OF INTC_CONTROL REG
			MOV R1, #01					@VALUE TO CLEAR BIT 0
			STR R1,[R0]					@WRITE TO INTC_CONTROL REG
			
			@MAKE SURE PROCESSOR IRQ ENABLED IN CPSR
			MRS R3, CPSR				@COPY CPSR TO R3
			BIC R3, #0x80				@CLEAR BIT 7
			MSR CPSR_c, R3				@WRITE BACK TO CPSR
			@TURN ON LED
SET:  	LDMFD SP!, {R0-R5,LR}	@RESTORE REGISTERS AND LR
		LDR R1,= 0x4804C000			@LOAD BASE ADDRESS OF GPIO1
		LDR R2,[R1,#0x013C]				@LOAD DATAOUT GPIO ADDRESS
		CMP R2, #0x00000000				@CHECK IF LED = 0
		BNE START
		LDR R3,=ADDRESSES		@RESET/SET VALUE TO TURN ON LED0															
       @TURN ON LED
 START:LDR R0,=0x4804C194		@LOAD ADDRESS OF GPIO_SETDATAOUT
       LDR R4, [R3]				@LOAD VALUE TO TURN ON LED                               
       STR R4,[R0]				@WRITE TO SETDATAOUT REG
       MOV R2, #0x0400000			@SET TIMER
       LOOP1:
       		NOP
       		SUBS R2,#1			@LOOP TO WAIT 1 SEC
       		BNE LOOP1
  
       @TURN OFF
       LDR R0,=0x4804C190		@LOAD ADDRESS OF GPIO1_CLEARDATAOUT REG
       STR R4,[R0]				@WRITE VALUE TO TURN OFF LED
       ADD R3, R3, #4
       CMP R4, #0x00C00000		@COMPARE VALUE TO BE LOADED (CHECK IF AT END OF SEQUENCE)
       BNE START				@IF LESS THAN THE HEX NUM, GO TO START
       B SET					@ELSE GO TO LED0
 		 	
 		 	
       			       	
.data
.align 2
ADDRESSES: .word 0x00600000, 0x01800000, 0x00C00000			
 .align 2
 SYS_IRQ:   .WORD 0
 .data
 .align 2
 STACK1:	.rept 1024
 			.word 0x0000
 			.endr
 STACK2:	.rept 1024
 			.word 0x0000
 			.endr
.end 
       
 
       
       
      @GPIO OUTPUTS TO SET AND VALUES TO TURN ON/OFF FOR EACH GPIO PIN (21-24)
      @21
      @ MOV R5,#0x00200000		@GPIO_22 TO HIGH WHEN OUPUT		(OUT 22 = 0100 = 4)
      @LDR R0,=0xFFDFFFFF		@SET GPIO22 AS OUTPUT
      
      @22
       @ MOV R5,#0x00400000		@GPIO_22 TO HIGH WHEN OUPUT		(OUT 22 = 0100 = 4)
       @LDR R0,=0xFFBFFFFF		@SET GPIO22 AS OUTPUT
       
       @23
       @ MOV R5,#0x00800000		@GPIO_22 TO HIGH WHEN OUPUT		(OUT 22 = 0100 = 4)
       @LDR R0,=0xFF7FFFFF		@SET GPIO22 AS OUTPUT
       
        @24
       @ MOV R5,#0x01000000		@GPIO_22 TO HIGH WHEN OUPUT		(OUT 22 = 0100 = 4)
       @LDR R0,=0xFEFFFFFF		@SET GPIO22 AS OUTPUT
        
 
		
.end