Interrupt enable and disable in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable interrupts in ARM architecture.

ARM Architecture

CPSIE [1]

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

AE

BF

CA

DI

Attempts:

3 left

💡 Hint

Common Mistakes

Using CPSIE F instead of CPSIE I

Confusing enable with disable instructions

The CPSIE I instruction enables IRQ interrupts by clearing the I bit in the CPSR register.

2fill in blank

medium

Complete the code to disable fast interrupts (FIQ) in ARM architecture.

ARM Architecture

CPSID [1]

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

AF

BI

CA

DE

Attempts:

3 left

💡 Hint

Common Mistakes

Using CPSID I instead of CPSID F

Mixing up enable and disable instructions

The CPSID F instruction disables FIQ interrupts by setting the F bit in the CPSR register.

3fill in blank

hard

Fix the error in the code to enable both IRQ and FIQ interrupts.

ARM Architecture

CPSIE [1]

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

AIF

BI

CF

DA

Attempts:

3 left

💡 Hint

Common Mistakes

Using CPSIE A which only affects asynchronous aborts (A bit)

Using only CPSIE I or CPSIE F to enable both

The CPSIE IF instruction enables both IRQ and FIQ interrupts by clearing the I and F bits in the CPSR register.

4fill in blank

hard

Fill both blanks to disable IRQ and FIQ interrupts respectively.

ARM Architecture

CPSID [1]
CPSID [2]

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

AI

BF

CA

DE

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same letter for both blanks

Using CPSIE instead of CPSID to disable interrupts

Use CPSID I to disable IRQ and CPSID F to disable FIQ interrupts.

5fill in blank

hard

Fill all three blanks to enable IRQ interrupts, disable FIQ interrupts, and enable asynchronous aborts respectively.

ARM Architecture

CPSIE [1]
CPSID [2]
CPSIE [3]

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

AF

BI

CA

DE

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up enable and disable instructions

Using wrong letters for IRQ and FIQ

CPSIE I enables IRQ interrupts by clearing the I bit, CPSID F disables FIQ interrupts by setting the F bit, and CPSIE A enables asynchronous aborts by clearing the A bit in the CPSR register.

Practice

1. What is the main purpose of disabling interrupts in ARM architecture?

easy

A. To prevent the processor from responding to events temporarily

B. To speed up the processor permanently

C. To reset the processor

D. To enable all hardware devices

Solution

1. Step 1: Understand what interrupts do

   Interrupts allow the processor to respond to events like input or timers.

2. Step 2: Understand disabling interrupts

   Disabling interrupts stops the processor from responding to these events temporarily, usually to protect critical code.

3. Final Answer:

   To prevent the processor from responding to events temporarily -> Option A

4. Quick Check:

   Disabling interrupts = stop event response temporarily [OK]

Hint: Disabling interrupts means stopping event responses temporarily [OK]

Common Mistakes:

• Thinking disabling interrupts speeds up the processor
• Confusing disabling interrupts with resetting the processor
• Believing disabling interrupts enables hardware devices

2. Which ARM assembly instruction is used to enable interrupts?

easy

A. CPSID i

B. MOV R0, #1

C. NOP

D. CPSIE i

Solution

1. Step 1: Recall interrupt enable instruction

   The instruction to enable interrupts in ARM is CPSIE i.

2. Step 2: Differentiate from disable instruction

   CPSID i disables interrupts, so it is not the correct answer.

3. Final Answer:

   CPSIE i -> Option D

4. Quick Check:

   Enable interrupts = CPSIE i [OK]

Hint: Enable interrupts with CPSIE i, disable with CPSID i [OK]

Common Mistakes:

• Confusing CPSIE i with CPSID i
• Choosing unrelated instructions like NOP or MOV
• Assuming CPSID i enables interrupts

3. What will happen if the following ARM instructions are executed in order?

CPSID i
CPSIE i

medium

A. Interrupts remain enabled

B. Interrupts remain disabled

C. Interrupts are first disabled then enabled

D. Processor resets

Solution

1. Step 1: Analyze first instruction CPSID i

   This disables interrupts, so after this instruction interrupts are off.

2. Step 2: Analyze second instruction CPSIE i

   This enables interrupts, so after this instruction interrupts are on again.

3. Final Answer:

   Interrupts are first disabled then enabled -> Option C

4. Quick Check:

   CPSID i then CPSIE i = disable then enable interrupts [OK]

Hint: CPSID disables, CPSIE enables interrupts in sequence [OK]

Common Mistakes:

• Assuming interrupts stay disabled after CPSIE i
• Thinking processor resets after these instructions
• Confusing the order of enable and disable

4. Identify the error in this ARM assembly snippet meant to disable interrupts:

CPSIE i

medium

A. No error, it disables interrupts correctly

B. It enables interrupts instead of disabling them

C. It resets the processor

D. Syntax error: missing register

Solution

1. Step 1: Understand the instruction CPSIE i

   CPSIE i is used to enable interrupts, not disable them.

2. Step 2: Compare with correct disable instruction

   The correct instruction to disable interrupts is CPSID i.

3. Final Answer:

   It enables interrupts instead of disabling them -> Option B

4. Quick Check:

   CPSIE i enables, not disables interrupts [OK]

Hint: CPSIE i enables interrupts; use CPSID i to disable [OK]

Common Mistakes:

• Confusing CPSIE i as disabling interrupts
• Thinking CPSIE i causes syntax error
• Believing CPSIE i resets processor

5. You want to protect a critical section of code from interrupts in ARM. Which sequence correctly disables interrupts before the section and enables them after?

hard

A. CPSID i before, CPSIE i after

B. CPSIE i before, CPSID i after

C. NOP before, CPSID i after

D. MOV R0, #0 before, MOV R0, #1 after

Solution

1. Step 1: Disable interrupts before critical section

   Use CPSID i to disable interrupts and protect the code.

2. Step 2: Enable interrupts after critical section

   Use CPSIE i to re-enable interrupts after the critical code finishes.

3. Final Answer:

   CPSID i before, CPSIE i after -> Option A

4. Quick Check:

   Disable then enable interrupts around critical code [OK]

Hint: Disable interrupts before, enable after critical code [OK]

Common Mistakes:

• Reversing enable and disable order
• Using unrelated instructions like NOP or MOV
• Not re-enabling interrupts after critical section