Loop implementation in assembly in ARM Architecture - Mini Project: Build & Apply

Loop implementation in assembly

📖 Scenario: You are learning how to write a simple loop in ARM assembly language. Loops help repeat a set of instructions multiple times, which is useful in many real-world tasks like counting, processing lists, or blinking an LED repeatedly.

🎯 Goal: Build a basic ARM assembly program that counts down from 5 to 1 using a loop and then stops.

📋 What You'll Learn

Create a register with the initial count value 5

Set up a label to mark the start of the loop

Use a decrement instruction to reduce the count by 1 each time

Use a conditional branch to repeat the loop while the count is not zero

💡 Why This Matters

🌍 Real World

Loops in assembly are used in embedded systems to repeat tasks like reading sensors, controlling motors, or blinking lights.

💼 Career

Understanding loops in assembly helps in low-level programming jobs such as embedded software development, firmware engineering, and systems programming.

1

DATA SETUP: Initialize the count register

Write an ARM assembly instruction to load the immediate value 5 into register r0. This will be our loop counter.

ARM Architecture

    MOV r0, #5  // Your code here

Need a hint?

Use the MOV instruction to put the number 5 into r0.

2

CONFIGURATION: Create the loop start label

Add a label called loop_start to mark the beginning of the loop.

ARM Architecture

    MOV r0, #5
loop_start:  // Your code here

Need a hint?

Labels end with a colon : and are placed at the start of a line.

3

CORE LOGIC: Decrement the counter and check if zero

Inside the loop, write an instruction to subtract 1 from r0. Then add a conditional branch instruction BNE loop_start to jump back to loop_start if r0 is not zero.

ARM Architecture

    MOV r0, #5
loop_start:
    SUB r0, r0, #1  // Your code here
    BNE loop_start  // Your code here

Need a hint?

Use SUB to decrease the value in r0. Use BNE to branch if not equal to zero.

4

COMPLETION: Add a stop instruction

Add the B . instruction after the loop to create an infinite stop (hang) so the program does not continue running random code.

ARM Architecture

    MOV r0, #5
loop_start:
    SUB r0, r0, #1
    BNE loop_start
    B .  // Your code here

Need a hint?

The instruction B . means branch to the current address, creating an infinite loop to stop the program.