ARM's 9 addressing modes

ARM's 9 addressing modes

1) Immediate addressing

The operand is an immediate value, prefixed with "#", and "0x" is used to represent a hexadecimal value.

example:

MOV R0,#0xFF00 ;0xFF00 -> R0

SUBS R0,R0,#1 ;R0 – 1 -> R0

2) Register addressing

The value of the operand is in the register, and the register value is directly taken out for operation when the instruction is executed.

example:

MOV R1,R2 ;R2 -> R1

SUB R0,R1,R2 ;R1 - R2 -> R0

3) Register offset addressing

When the second operand is in register shift mode, the second register operand is selected for shift operation before being combined with the first operand.

example:

MOV R0,R2,LSL #3 ; Shift the value of R2 left by 3 bits and put the result into R0, i.e. R0 = R2 * 8

ANDS R1,R1,R2,LSL #3 ; The value of R2 is shifted left by 3 bits, and then ANDed with R1, and the result is placed in R1

Available shift operations:

LSL: Logical Shift Left, fill the empty bits at the low end with 0

LSR: Logical Shift Right, fill the high-end vacant bits with 0

ASR: Arithmetic Shift Right. The sign bit remains unchanged during the shift process. If the source operand is a positive number, the high-end vacant bit is filled with 0, otherwise it is filled with 1.

ROR: Rotate Right, fill the empty bits at the high end with the bits at the low end

RRX: Rotate Right eXtended by 1 place, the operand is shifted right by one place, and the high-end vacant bit is filled with the original C flag value.

4) Register indirect addressing

The operand is stored in the storage unit at the address specified by the register, that is, the register is the address pointer of the operand.

example:

LDR R1,[R2]; Use the value in R2 as the address, take out the data in this address and save it in R1

SWP R1,R1,[R2] ; Use the value in R2 as the address, and take out the value in this address and the value in R1**

5) Base addressing

Add the value of the base register to the offset to form the effective address of the operand. Base addressing is used to access storage units near the base address and is often used for table lookup, array operations, function register access, etc. 

example:

LDR R2,[R3,#0x0F] ; Add 0x0F to the value in R3 as the address, and save the value at this address in R2

STR R1,[R0,#-2] ; Subtract 2 from the value in R0 as the address and save the value of R1 to this address

6) Multi-register addressing

Transfer multiple register values ​​at a time, allowing one instruction to transfer any subset or all of the 16 registers. When addressing multiple registers, the register subsets are arranged in order from small to large. Continuous registers can be connected with "-", otherwise, they are separated by ",".

example:

LDMIA R1!,{R2-R7,R12}; Read the value of R1 to R2-R7, R12, and R1 will automatically increase by 1 during the process

STMIA R0!,{R3-R6,R10}; save the values ​​of R3-R6, R10 to the address pointed to by R0, and R0 is automatically increased by 1 during the process

7) Stack addressing

Stack addressing uses the stack pointer SP, which is R13, to point to the top of the stack. The stack can be divided into two types:

Growing upward: Growing toward higher addresses is called an incremental stack.

Growing downward: Growing towards lower addresses is called a descending stack.

The stack pointer points to the last valid data item pushed in, which is called a full stack.

The stack pointer points to the next empty location to be placed, called the empty stack, so there are 4 types of stacks.

A) Full increment: The stack address increases upward, and the stack pointer points to the highest address of valid data, such as LDMFA, STMFA.

B) Empty increment: The stack address grows upward, and the stack pointer points to the first empty location on the stack, such as LDMEA, STMEA.

C) Full decrement: The stack address grows downward, and the stack pointer points to the lowest address of the valid data item, such as LDMFD, STMFD.

D) Empty decrement: The stack address grows downward, and the stack pointer points to the first empty location under the stack. Such as LDMED, STMED.

example:

STMFD SP!,{R1-R7,LR} ; Push R1 to R7, LR into the stack. Decrement the stack when it is full.

LDMFD SP!,{R1-R7,LR} ; Pop the data from the stack and put it into registers R1~R7,LR. Full decrement stack.

8) Block copy addressing

Used to copy a block of data from one location in memory to another.

example:

STMIA R0!,{R1-R7}; Save the data of R1~R7 to the memory. The memory pointer increases after saving the first value, and the growth direction is upward.

STMIB R0!,{R1-R7}; Save the data of R1~R7 to the memory. The memory pointer increases before saving the first value, and the growth direction is upward.

STMDA R0!,{R1-R7}; Save the data of R1~R7 to the memory. The memory pointer increases after saving the first value, and the growth direction is downward.

STMDB R0!,{R1-R7}; Save the data of R1 to R7 to the memory. The memory pointer increases before saving the first value, and the growth direction is downward.

9) Relative addressing

Relative addressing is a variation of base addressing. The program counter PC provides the base address. The address in the instruction

The code field is used as the offset, and the two are added together to obtain the effective address.

example:

BL ROUTE1 ;Call ROUTE1 subroutine

BEQ LOOP; Conditional jump to LOOP label

…

LOOP MOV R2,#2

…

ROUTE1

…