Exception priority levels in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to identify the highest priority exception type in ARM architecture.

ARM Architecture

The highest priority exception in ARM is the [1] exception.

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ASoftware Interrupt

BUndefined Instruction

CReset

DPrefetch Abort

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing Reset with Software Interrupt as highest priority.

The Reset exception has the highest priority in ARM architecture because it initializes the processor.

2fill in blank

medium

Complete the sentence to identify which exception has lower priority than IRQ in ARM.

ARM Architecture

In ARM, the [1] exception has lower priority than IRQ.

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AFIQ

BUndefined Instruction

CReset

DPrefetch Abort

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up FIQ and IRQ priorities.

Undefined Instruction exception has lower priority than IRQ. FIQ has higher priority than IRQ.

3fill in blank

hard

Fix the error in the priority order: FIQ > {{BLANK_1}} > IRQ.

ARM Architecture

The correct priority order is FIQ > [1] > IRQ.

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APrefetch Abort

BReset

CSoftware Interrupt

DUndefined Instruction

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing Reset or Software Interrupt incorrectly.

Prefetch Abort has higher priority than IRQ but lower than FIQ in ARM exception priority.

4fill in blank

hard

Fill both blanks to complete the ARM exception priority order: {{BLANK_1}} > {{BLANK_2}} > IRQ.

ARM Architecture

The priority order is [1] > [2] > IRQ.

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AFIQ

BPrefetch Abort

CUndefined Instruction

DSoftware Interrupt

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping Prefetch Abort and Undefined Instruction.

FIQ has the highest priority, followed by Prefetch Abort, then IRQ in ARM exception priority.

5fill in blank

hard

Fill all three blanks to complete the ARM exception priority order: {{BLANK_1}} > {{BLANK_2}} > {{BLANK_3}}.

ARM Architecture

The priority order is [1] > [2] > [3].

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AReset

BFIQ

CIRQ

DUndefined Instruction

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing IRQ with FIQ priority.

Reset has the highest priority, followed by FIQ, then IRQ in ARM exception priority levels.

Practice

1. In ARM architecture, what does a lower exception priority number indicate?

easy

A. No priority assigned

B. Lower priority for handling the exception

C. Higher priority for handling the exception

D. Equal priority to all exceptions

Solution

1. Step 1: Understand priority numbering in ARM

   In ARM processors, exception priority levels use numbers where lower numbers mean higher priority.

2. Step 2: Interpret the meaning of lower numbers

   A lower number means the exception is handled before others with higher numbers.

3. Final Answer:

   Higher priority for handling the exception -> Option C

4. Quick Check:

   Lower number = Higher priority [OK]

Hint: Lower number means higher priority in ARM exceptions [OK]

Common Mistakes:

• Thinking higher numbers mean higher priority
• Assuming all exceptions have equal priority
• Confusing priority with exception type

2. Which of the following correctly represents the priority order in ARM exception levels from highest to lowest?

easy

A. 3, 2, 1, 0

B. 0, 1, 2, 3

C. 1, 0, 3, 2

D. 2, 3, 0, 1

Solution

1. Step 1: Recall ARM priority numbering

   Lower numbers indicate higher priority, so priority order starts from 0 upwards.

2. Step 2: Arrange numbers from lowest to highest

   The correct order from highest to lowest priority is 0, 1, 2, 3.

3. Final Answer:

   0, 1, 2, 3 -> Option B

4. Quick Check:

   Priority order = 0 to 3 [OK]

Hint: Priority order counts up from 0 as highest [OK]

Common Mistakes:

• Reversing the order thinking higher numbers are higher priority
• Mixing up the sequence of numbers
• Assuming priority starts at 1 instead of 0

3. Given these exception priorities in ARM: IRQ = 2, FIQ = 0, SVC = 1, which exception will be handled first?

medium

A. FIQ

B. IRQ

C. SVC

D. All handled simultaneously

Solution

1. Step 1: Identify priority numbers for each exception

   FIQ has priority 0, SVC has 1, IRQ has 2.

2. Step 2: Determine which priority is highest

   Lower number means higher priority, so FIQ with 0 is handled first.

3. Final Answer:

   FIQ -> Option A

4. Quick Check:

   Lowest number (0) = FIQ first [OK]

Hint: Exception with priority 0 handled first [OK]

Common Mistakes:

• Choosing IRQ because it sounds more common
• Assuming SVC is highest priority by name
• Thinking all exceptions run at the same time

4. If an ARM system incorrectly assigns a higher number to a critical exception, what is the likely problem?

medium

A. The critical exception may be delayed or ignored

B. The system will crash immediately

C. All exceptions will have equal priority

D. The critical exception will run first anyway

Solution

1. Step 1: Understand priority impact on handling

   Higher numbers mean lower priority, so a critical exception with a high number is handled later.

2. Step 2: Predict system behavior

   This delay can cause the critical exception to be delayed or missed, affecting system reliability.

3. Final Answer:

   The critical exception may be delayed or ignored -> Option A

4. Quick Check:

   Wrong priority number delays critical exception [OK]

Hint: Critical exceptions need lowest priority number [OK]

Common Mistakes:

• Assuming system crashes immediately
• Thinking priority numbers do not affect handling
• Believing all exceptions run equally regardless of priority

5. You have three exceptions with priorities: Timer = 1, UART = 3, Reset = 0. If Timer, UART, and Reset exceptions occur simultaneously, which will ARM handle first and why?

hard

A. UART, because it has the highest number

B. Timer, because it occurs first

C. Timer, because it has a medium priority

D. Reset, because it has the lowest number

Solution

1. Step 1: Identify priorities and exceptions involved

   Reset has priority 0, Timer 1, UART 3. Timer, UART, and Reset occur simultaneously.

2. Step 2: Determine which exception ARM handles first

   ARM handles the exception with the lowest priority number first, which is Reset with 0.

3. Step 3: Understand simultaneous exceptions handling

   Since Reset has the highest priority, it preempts others.

4. Final Answer:

   Reset, because it has the lowest number -> Option D

5. Quick Check:

   Lowest number = highest priority = Reset first [OK]

Hint: Lowest priority number exception handled first always [OK]

Common Mistakes:

• Overlooking Reset's highest priority
• Picking Timer due to medium priority
• Choosing UART because it occurs simultaneously