comm

ES/Lab/Lab2/swap/LOOP2.asm

@@ -1,27 +1,83 @@
-	AREA RESET, DATA, READONLY
-	EXPORT __Vectors
-__Vectors
-	DCD 0x10001000
-	DCD Reset_Handler
-	ALIGN
-	AREA mycode,CODE,READONLY
-	ENTRY
-	EXPORT Reset_Handler
+; ========================================================================================
+; LOOP2.asm - Array Copy Using Loop with Proper Destination Array Size
+; ========================================================================================
+; This program demonstrates the same array copy algorithm as LOOP.asm but with
+; two key improvements:
+; 1. Uses R12 as the loop counter (R12 is typically used for intra-procedure calls)
+; 2. Pre-allocates the correct size for the destination array (10 elements)
+; This version is more complete and avoids potential memory issues.
+
+	AREA RESET, DATA, READONLY        ; Define a read-only data section for the vector table
+	EXPORT __Vectors                  ; Export the vector table for external linking
+
+__Vectors                             ; Start of the vector table
+	DCD 0x10001000                    ; Stack pointer initial value (points to top of stack)
+	DCD Reset_Handler                 ; Address of the reset handler (program entry point)
+	ALIGN                             ; Ensure proper alignment for the next section
+
+	AREA mycode,CODE,READONLY         ; Define the code section as read-only
+	ENTRY                             ; Mark the entry point of the program
+	EXPORT Reset_Handler             ; Export the reset handler function
+
+; ========================================================================================
+; Reset_Handler - Main program execution
+; ========================================================================================
+; Algorithm Overview:
+; 1. Initialize array pointers (R0 = SRC address, R1 = DST address)
+; 2. Set loop counter R12 to the number of elements to copy (10)
+; 3. In each iteration of the loop:
+;    a. Load element from SRC array using post-increment addressing
+;    b. Store element to DST array using post-increment addressing
+;    c. Decrement counter and check if more iterations are needed
+; 4. This version properly allocates destination array space beforehand
 Reset_Handler
-	LDR R0, =SRC          
-	LDR R1, =DST          
-	MOV R12, #10          
+	; Step 1: Initialize array pointers
+	; R0 points to the beginning of the source array
+	LDR R0, =SRC                      ; R0 = address of first element in SRC array
 
+	; R1 points to the beginning of the destination array
+	LDR R1, =DST                      ; R1 = address of first element in DST array
+
+	; Step 2: Initialize loop counter
+	; R12 holds the number of elements to copy (10 elements total)
+	; Using R12 is a common convention for loop counters in ARM assembly
+	MOV R12, #10                      ; R12 = 10 (number of elements to copy)
+
+	; Step 3: Main copy loop
 Loop
-	LDR R2, [R0], #4      
-	STR R2, [R1], #4      
-	SUBS R12, R12, #1     
-	BNE Loop             
+	; Load from SRC array and advance pointer
+	; LDR R2, [R0], #4 means: R2 = [R0], then R0 = R0 + 4
+	LDR R2, [R0], #4                  ; Load next element from SRC and advance R0
 
+	; Store to DST array and advance pointer
+	; STR R2, [R1], #4 means: [R1] = R2, then R1 = R1 + 4
+	STR R2, [R1], #4                  ; Store element to DST and advance R1
+
+	; Decrement loop counter and set condition flags
+	; SUBS R12, R12, #1 is equivalent to SUBS R12, #1
+	SUBS R12, R12, #1                 ; R12 = R12 - 1 (set flags for branch condition)
+
+	; Branch back to Loop if R12 is not zero
+	BNE Loop                          ; If R12 != 0, continue loop
+
+	; Step 4: Program termination
+	; Create an infinite loop to stop program execution
 STOP
-	B STOP                
-	ALIGN
+	B STOP                            ; Branch to STOP label (infinite loop)
+
+	ALIGN                             ; Ensure proper alignment for data section
+
+; ========================================================================================
+; Data Section - Source and Destination Arrays
+; ========================================================================================
+; SRC array contains 10 elements (40 bytes total):
+; Each element is a 32-bit word in hexadecimal format
 SRC DCD 0x00000032, 0x12345644, 0x00000005, 0x00000098, 0x000000AB, 0x000000CD, 0x00000055, 0x00000032, 0x000000CA, 0x00000045
-	AREA mydate, DATA, READWRITE
+
+	AREA mydate, DATA, READWRITE      ; Define a read-write data section
+
+; DST array - properly pre-allocated with 10 elements (all initialized to 0)
+; This ensures there is enough space for all copied elements
 DST DCD 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
-	END
+
+	END                               ; End of the assembly program