ADDgt.s

;The semicolon is used to lead an inline documentation
;When you write your program, you could have your info at the top document lock
;For Example:  Your Name, Student Number, what the program is for, and what it does etc.

;;; Directives
          PRESERVE8
          THUMB       
 
; Vector Table Mapped to Address 0 at Reset
; Linker requires __Vectors to be exported
 
          AREA    RESET, DATA, READONLY
          EXPORT  __Vectors
 
__Vectors 
	  DCD  0x20001000     ; stack pointer value when stack is empty
          DCD  Reset_Handler  ; reset vector
  
          ALIGN
		  
;Your Data section
	;AREA DATA
SUM 	DCD 0
SUMP    DCD SUM
N 	DCD 7
NUM1 	DCD 3, -7, 2, -2, 10, 20, 30
POINTER DCD NUM1

 
; The program
; Linker requires Reset_Handler
 
          AREA    MYCODE, CODE, READONLY
 
   	  ENTRY
   	  EXPORT Reset_Handler
 
 
Reset_Handler

;;;;;;;;;;User Code Start from the next line;;;;;;;;;;;;

	LDR R1, N	; load size of array - 
			    ; a counter for how many elements are left to process
	LDR R2, POINTER		; load base pointer of array

	MOV R0, #0		; initialize accumulator
	
	;3, -7, 2, -2, 10, 20, 30
LOOP 	
	LDR R3, [R2], #4	; load value from array,  AUTO-INDEX
						; increment array pointer to next word
	CMP R3, #5			; compare curent val with 5 
	BGT over5 			; if current is greater than 5 branch
GOTO
	;ADD R0, R0, R3		; add value from array to accumulator
	SUBS R1, R1, #1		; decrement work counter
	BGT LOOP			; keep looping until counter is zero
	
	LDR R4, SUMP		; WORKS - I can see address of SUMP in R4
	STR R0, [R4]		; CAN't TELL - no reaction so don't know. PC does change tho.
	
	LDR R6, [R4]		; DOESN'WORK - nothing in R6. Don't know why.
	
	B STOP

;sub-routine
over5
	ADD R0, R0, R3 		; add curent val to sum
	B GOTO
	

STOP  
	B  STOP

	END 

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