ARM Assembly Language Instructions

Questions and Answers

What is a key feature of the ARM instruction set architecture?

Load-store architecture

How many operands can be processed in a single data processing instruction?

3 operands

What is the result size of a multiply instruction in ARM?

64-bit

What is the purpose of the condition field in ARM instructions?

To enable conditional execution Signup and view all the answers

What is the effect of the MOVS instruction on the flags?

The Z flag is set, and the C and V flags are unaffected Signup and view all the answers

How many possible machine instructions are there in ARM?

232 Signup and view all the answers

What is the purpose of the MVN instruction in the given code?

To move the negated value of R22 to R0 Signup and view all the answers

What is the effect of the instruction 'MOV R0, R2, ROR #2' on the register R2?

R2 is unchanged Signup and view all the answers

In the instruction 'ADD R0, R1, R2', what is the role of R1 and R2?

R1 and R2 are the operands being added together Signup and view all the answers

What is the significance of the bottom 8 bits of the register in shifted register operands?

The bottom 8 bits specify the number of bits to be shifted Signup and view all the answers

What is the difference between the ROR and RRX instructions?

ROR rotates right by an immediate value, while RRX rotates right by a register value Signup and view all the answers

What is the effect of the instruction 'MOV R0, 0' on the register R0?

R0 is set to 0 Signup and view all the answers

What is the purpose of the 'cond' field in the instruction encoding?

Set the condition codes Signup and view all the answers

What is the function of the 'v' field in the instruction encoding?

Indicate the presence of an immediate operand Signup and view all the answers

What is the range of immediate values that can be loaded using a single instruction?

0 to 31 Signup and view all the answers

What is the purpose of the 'Rn' field in the instruction encoding?

Select the first operand register Signup and view all the answers

What is the function of the 'Sh' field in the instruction encoding?

Specify the shift length Signup and view all the answers

What is the purpose of the 'Rm' field in the instruction encoding?

Specify the second operand register Signup and view all the answers

What is the function of the 'opcode' field in the instruction encoding?

Determine the arithmetic/logic function Signup and view all the answers

What is the purpose of the 'imm' field in the instruction encoding?

Specify the immediate operand Signup and view all the answers

What is the addressing mode where the calculation is done before accessing the memory with a writeback?

Auto-indexing addressing Signup and view all the answers

What is the result of the instruction LDR R0, [R1, #4]?

R0 = mem[R1 + 4], R1 unchanged Signup and view all the answers

Which addressing mode is used in the instruction LDR R0, [R1, R2]?

Register addressing Signup and view all the answers

What is the effect of the writeback in auto-indexing addressing?

It updates the base register with the new address Signup and view all the answers

What is the result of the instruction LDR R0, [R1, R2, LSL #2]?

R0 = mem[R1 + 4*R2], R1 unchanged Signup and view all the answers

What is the difference between pre-index and post-index addressing?

Post-index addressing updates the base register, while pre-index addressing does not Signup and view all the answers

Which addressing mode is used in the instruction LDR R0, [R1], #4?

Post-index addressing Signup and view all the answers

What is the advantage of auto-indexing addressing?

It is faster than pre-index addressing Signup and view all the answers

What is the guideline for loading constants into a register?

Use two instructions if possible, otherwise load it. Signup and view all the answers

How can you load the value 511 into R0 using the fewest number of instructions?

Using the mov and add instructions. Signup and view all the answers

What is the purpose of the ADR instruction in the example code?

To load the address of label 'a' into R1. Signup and view all the answers

What is the mode of addressing used in the instruction 'ldr r0, [pc, #4]'?

PC-relative addressing mode. Signup and view all the answers

What is the sequence of operations performed by the CPU during the execution of an instruction?

Fetch, decode, execute. Signup and view all the answers

What is the purpose of the instruction 'SWI #11' in the example code?

To perform a software interrupt. Signup and view all the answers

Study Notes

ARM Instruction Set

232 possible machine instructions, structured into:
- Load-store architecture
- 3-address instructions
- Conditional execution of every instruction
- Load/store multiple registers at once
- Combine shift and ALU operations in a single instruction

Data Processing

Instructions: move, arithmetic, logical, comparison, and multiply
Most data processing instructions process one operand using the barrel shifter
General rules:
- All operands are 32-bit, coming from registers or literals
- Result is 32-bit and placed in a register (except for long multiply, which produces a 64-bit result)
- 3-address format

Conditional Execution

Almost all ARM instructions have a condition field, allowing conditional execution
Example: MOVCS R0, R1 @ if carry is set, then R0:=R1

Register Movement

MOV instruction: MOV R0, R2 @ R0 = R2
MVN instruction: MVN R0, R2 @ R0 = ~R2 (move negated)

Addressing Modes

Register operands: ADD R0, R0, R1
Immediate operands: ADD R0, R0, #4
Rotate right: MOV R0, R2, ROR #2 @ R0:=R2 rotate right 2
Rotate right extended: MOV R0, R2, RRX @ R0:=R2 rotate right extended
Shifted register operands: use a register to specify the number of bits to be shifted

Load and Store

Load: LDR R0, [R1] @ mem[R1]
Store: STR R0, [R1] @ mem[R1]
Addressing modes:
- Pre-index: LDR R0, [R1, #4]
- Auto-indexing: LDR R0, [R1, #4]!
- Post-index: LDR R0, [R1], #4

Comparisons

Pre-indexed addressing: LDR R0, [R1, R2] @ R0=mem[R1+R2]
Auto-indexing addressing: LDR R0, [R1, R2]! @ R0=mem[R1+R2]
Post-index addressing: LDR R0, [R1], R2 @ R0=mem[R1]

Load Constants

Assemblers implement loading constants using two options:
- Construct it in multiple instructions
- Load it from memory
Guideline: if you can construct it in two instructions, do it; otherwise, load it

PC-relative Addressing

Impossible to use direct addressing encoding for data transfer instructions
Example: ADR R1, a @ add r1, pc, #4
PC-relative addressing mode: LDR R0, [PC, #0]

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Description

This quiz covers ARM assembly language instructions for register movement, addressing modes, and immediate operands. It includes examples of MOV, MVN, and ADD instructions with register and immediate operands.