Why subroutines enable modular assembly code in ARM Architecture - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call a subroutine named 'process_data'.

ARM Architecture

BL [1]

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Astart

Bmain_loop

Cend_program

Dprocess_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using a label that is not a subroutine.

Confusing BL with other branch instructions.

The BL instruction calls the subroutine named process_data, enabling modular code reuse.

2fill in blank

medium

Complete the code to return from a subroutine.

ARM Architecture

[1]

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ABX LR

BMOV PC, R0

CB main

DBLX R1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a branch to a fixed label instead of LR.

Confusing return with a call instruction.

The instruction BX LR returns control to the calling function by branching to the address stored in the link register.

3fill in blank

hard

Fix the error in the subroutine call to correctly save the return address.

ARM Architecture

BL [1]

Drag options to blanks, or click blank then click option'

Amain

Bstart_loop

Cprocess_data

Dreturn

Attempts:

3 left

💡 Hint

Common Mistakes

Using a label that is not a subroutine.

Using a branch instruction that does not save the return address.

The BL instruction saves the return address in the link register and branches to process_data, enabling modular calls.

4fill in blank

hard

Fill both blanks to create a subroutine that saves and restores registers.

ARM Architecture

PUSH [1]
...
POP [2]

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A{LR}

B{R4-R7}

C{R0-R3}

D{PC}

Attempts:

3 left

💡 Hint

Common Mistakes

Saving and restoring different registers.

Not saving registers that the subroutine modifies.

Saving registers {R4-R7} before subroutine work and restoring them after preserves their values, enabling modular code.

5fill in blank

hard

Fill all three blanks to define a modular subroutine that takes input, processes it, and returns.

ARM Architecture

MOV R0, [1]
BL [2]
[3]

Drag options to blanks, or click blank then click option'

Ainput_value

Bprocess_data

CBX LR

DR1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong register for input.

Forgetting to return properly from the subroutine.

This code moves the input value into R0, calls the process_data subroutine, and returns using BX LR, demonstrating modular assembly.