Exception entry and exit sequence in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the first step in the ARM exception entry sequence.

ARM Architecture

The processor first [1] the current program counter (PC) to the link register (LR).

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Aloads

Bstores

Cignores

Dmodifies

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing loading with storing the PC.

Thinking the PC is ignored during exception entry.

During exception entry, the ARM processor saves the current PC to the LR to remember where to return after handling the exception.

2fill in blank

medium

Complete the code to describe what happens to the processor mode during exception entry.

ARM Architecture

The processor switches to [1] mode to handle the exception safely.

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AUser

BSystem

CSupervisor

DAbort

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing User mode which is unprivileged.

Confusing Abort mode with general exception handling mode.

ARM processors switch to Supervisor mode during exception entry to run privileged exception handlers.

3fill in blank

hard

Fix the error in the description of the exception exit sequence.

ARM Architecture

During exception exit, the processor [1] the saved PC from the LR and resumes normal execution.

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Aloads

Bmodifies

Cstores

Dignores

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking the processor stores the PC again during exit.

Assuming the processor ignores the LR value.

On exception exit, the processor loads the saved PC from the LR to continue execution where it left off.

4fill in blank

hard

Fill both blanks to complete the ARM exception entry sequence steps.

ARM Architecture

The processor [1] the current CPSR to SPSR, then [2] the PC to the exception vector address.

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Acopies

Bloads

Cstores

Djumps

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing storing with copying the CPSR.

Using 'loads' instead of 'jumps' for PC movement.

During exception entry, the current CPSR is copied to SPSR to save status, then the PC jumps to the exception vector address to start handling.

5fill in blank

hard

Fill all three blanks to describe the exception exit sequence correctly.

ARM Architecture

The processor [1] the SPSR back to CPSR, [2] the PC from LR, and then [3] normal execution.

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Arestores

Bloads

Cresumes

Dstores

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'stores' instead of 'restores' for CPSR.

Confusing the order of operations during exit.

On exception exit, the processor restores the saved status from SPSR to CPSR, loads the PC from LR, and resumes normal execution.