6. ARM addressing mode

The addressing mode is for the source operand.

6.1 Immediate addressing

• The source operand is an immediate value

• Immediate number: The number starting with the # sign in the opcode is the immediate number.

• Immediate addressing: MOV R0, #0x300

• Pseudo-instruction: LDR R0,=0x12345678

• Notice:

• The immediate data is 8-bit data storage, represented by

• The immediate value 0xf200 is indirectly represented by 0xcf2, that is, the 8-bit F2 is rotated right by 24 bits (2 * 12) to obtain X = 0xf2; Y = 0xC

6.2 Register addressing

• MOV R0,R1

• The source operand is a register

6.3 Register shift addressing

• Shift the source operand addressed by the register

• MOV R0, R2, LSL, #3

• After shifting R2 to the left by 3 bits, assign it to R0

6.4 Register indirect addressing

• ARM consists of L/S structure, namely load/store

• LOAD loads memory data into registers

• STROE stores the data in the register into memory

• instruction:

• LDR R0, {R1} take out the value in {R1} and put it into R0

• STR R0, {R1} Take out the value in R0 and put it into R1

• {R1} means taking the data in the address stored in R1 and replacing it with C language, that is, *R1

1 MOV R1, #0x40000000

2 LDR R0, {R1}

3 STR R0, {R1}

4 

5 //If the data represented by the data 0x40000000 in R1 is 0x55, then the value of R0 is 0x55

6.5 Base address indexed addressing

• MOV R0, #44

• MOV R1, #0x40000008

• STR R0, [R1, #-4]

• [R1, #-4] means the address value stored in R1 - 4

• #-4 represents the offset

• STR R0, [R1, #-4]!

• ! means write-back, which is i-- in C language. The previous sentence first assigns the address value of R1 to R0, and then assigns the value in R0 - 4

• The previous sentence is equivalent to STR R0,[R1], #-4

6.6 Multiple register addressing

• STMIA R0!, {R1 - R3, R5}

• Store the values ​​in R1 R2 R3 R5 in the address space starting from R0

• The content in curly brackets represents the value in the register, and R0 corresponds to the memory address.

• STM: Manipulate the values ​​of multiple memories

• The corresponding command is LDMIA

• I/D (increase/decrease) A/B (after/before)

6.7 Stack addressing

• To perform stack operations, the stack register is R13, which is the SP register.

• STMFD SP!, {R1-R3} push onto the stack, the register with the larger number is pushed onto the stack first, it has nothing to do with the writing order.

• LDMFD SP!, {R1-R3} pop

• Combination: F(FULL)/E(EMPTY) I/D

• Generally written as FD, because the address space of ARM is full-decreasing.

• Full stack: The stack pointer points to the last valid data item pushed

• Empty stack: The stack pointer points to the next empty location to be pushed.

• MOV SP, #0x40000010

• STMFD SP!, {R1-R4}

• That is, the value of R4 R3 R2 R1 is stored in 0x4000000c 0x40000008 0x40000004 0x40000000

6.8 Relative addressing

• The jmp and call instructions used in 51

• Relative addressing is a jump. Relative addressing is relative to the PC. Jump instruction: B BL BLX BX

• B: jump instruction

• BL: Jump instruction with return

• BLX: Jump instruction with return and state switching

• BX: Jump instruction with status switching