ARM data load and store instructions (I)

 
Experimental purpose:
l         Application of single register data transfer instructions and master of various displacement addressing modes
l         Application of multi-register data transfer instructions and master of various displacement addressing modes
l         Methods of single data copying and data block copying.
l         Use various windows in the debugger to observe the changes of registers, memory, label addresses, machine instructions, etc. after completing each instruction operation.
1. Single register load and store instructions LDR|STR
      AREA Lab1,CODE
      ENTRY
START 
      ADR R1,SRC
       ADR R2,DST
COPY   
      LDR R0,[R1]
      STR R0,[R2]
      ADD R1,R1,#0x4
      ADD R2,R2,#0x4
      LDR R0,[R1]
      STR R0,[R2]
      ADD R1,R1,#0x4
      ADD R2,R2, #0x4
      LDR R0,[R1]
      STR R0,[R2]
      
STOP
      B STOP
       
      
SRC    DCB "one small!"
      ALIGN
DST    DCB "three big!"
      END
Program Description:
1.       The pseudo-instruction ADR stores the address of a register-related expression or a program-related expression into a register. In the example, it is equivalent to making R1 point to SRC and R2 point to DST, that is, initializing the address pointer.
2.       The function of DCB is to allocate a group of bytes of memory and define its content as a specified string. It can also be replaced by "=":
SRC = "one small!"
DST = "three big!"
 
Complete the following tasks
1. Read the program exp6_1.s and write out the function of the program. Set the base address of the code segment to 0x8000. Use AXD to debug the program step by step, observe the changes in the corresponding registers and memory after each step, and complete the table.
The opened process view window is as follows: register, disassembly, low lever symbols, memory

Serial number

Execute Instructions

Changes after instruction execution

register

Memory

R0

R1

R2

PC

0x8040

0x8041

0x8042

0x8043

0x8044

0x8045

0x8046

0x8047

0x8048

0x8049

0

0x0

0x0

0x0

0x8000

0x74 t

0x68 H

0x72 r

0x65e ​

0x65e ​

0x20 _

0x62 b

0x69 i

0x67 g

0x21 !

1

2

3

4

5

6

7

8

9

10

2. The addressing mode used in the program is the zero-displacement mode in indirect addressing. Please change the program to the pre-displacement form and post-displacement form. (Draw a diagram to analyze various displacement addressing forms and design a program to verify.)
3. Use the multi-register transfer instruction to modify the program.
 
Answer:
1.       The function of the program is to transfer the source data at SRC in the memory to DST through the data transfer instruction.
2.       Pre- and post-addressing
Method 1
COPY LDR R0,[R1],#4
           STR R0,[R2],#4
           LDR R0,[R1],#4
           STR R0,[R2],#4
LDR R0,[R1],#4
           STR R0,[R2],#4
Method 2
   SUB R1,R1,#4
   SUB R2,R2,#4
   MOV R3,#1
CPY
   LDR R0,[R1,#4]!
   STR R0,[R2,#4]!
   CMP R3,#3
   ADD R3,R3,#1
   BNE CPY
Method 3
LDR R0,[R1]
           STR R0,[R2]
           LDR R0,[R1，#4]
           STR R0,[R2，#4]
LDR R0,[R1，#8]
           STR R0,[R2，#8]