Vector table relocation in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the Vector Table Offset Register (VTOR) to a new address.

ARM Architecture

SCB->VTOR = [1];

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

A0x08000000

B0x20000000

C0x00000000

D0x1FFF0000

Attempts:

3 left

💡 Hint

Common Mistakes

Using RAM address instead of flash address for VTOR.

Setting VTOR to zero which points to default vector table location.

The VTOR register holds the base address of the interrupt vector table. Setting it to 0x08000000 points to the start of flash memory where the relocated vector table is typically placed.

2fill in blank

medium

Complete the code to relocate the vector table to RAM at address 0x20000000.

ARM Architecture

SCB->VTOR = [1];

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

A0x08000000

B0x00000000

C0x1FFF0000

D0x20000000

Attempts:

3 left

💡 Hint

Common Mistakes

Using flash address instead of RAM address for relocation.

Forgetting to copy the vector table to the new RAM location.

Relocating the vector table to RAM requires setting VTOR to the RAM base address, which is typically 0x20000000 on ARM Cortex-M devices.

3fill in blank

hard

Fix the error in the code that attempts to relocate the vector table but uses an incorrect address.

ARM Architecture

SCB->VTOR = [1];

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

A0xFFFFFFFF

B0x20000000

C0x08000000

D0x00000000

Attempts:

3 left

💡 Hint

Common Mistakes

Using an invalid or undefined memory address for VTOR.

Confusing zero address with valid vector table location.

The correct relocation address for the vector table in flash memory is 0x08000000. Using 0x00000000 or 0xFFFFFFFF is invalid and causes errors.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps interrupt names to their new vector addresses after relocation.

ARM Architecture

new_vectors = [1]: base_address + offset for base_address, offset in vectors.items() if offset [2] 0

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

Ainterrupt

B>

C==

Dvector

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect key names in comprehension.

Using equality instead of greater than for filtering.

The dictionary comprehension uses interrupt as the key and filters offsets greater than zero with > to include valid vectors.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that relocates vectors with uppercase keys and filters valid offsets.

ARM Architecture

relocated = [1]: [2] for [3], offset in vectors.items() if offset > 0}

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

Ainterrupt.upper()

Boffset

Cinterrupt

Dvector

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase keys instead of uppercase.

Mixing up keys and values in comprehension.

The comprehension uses interrupt.upper() as keys, offset as values, and iterates over interrupt and offset from the vectors dictionary.

Practice

1. What is the primary purpose of relocating the vector table in ARM architecture?

easy

A. To increase the processor clock speed

B. To change the base address where interrupt handlers are located

C. To enable floating-point operations

D. To disable interrupts permanently

Solution

1. Step 1: Understand the vector table role

   The vector table contains addresses of interrupt handlers used by the processor.

2. Step 2: Purpose of relocation

   Relocation changes the base address so the processor knows where to find these handlers in memory.

3. Final Answer:

   To change the base address where interrupt handlers are located -> Option B

4. Quick Check:

   Vector table relocation = changing interrupt handler base address [OK]

Hint: Vector table relocation changes interrupt handler address base [OK]

Common Mistakes:

• Confusing relocation with clock speed changes
• Thinking relocation disables interrupts
• Assuming relocation enables floating-point

2. Which ARM register is used to relocate the vector table base address?

easy

A. VTOR (Vector Table Offset Register)

B. SP (Stack Pointer)

C. LR (Link Register)

D. PC (Program Counter)

Solution

1. Step 1: Identify the register for vector table base

   The VTOR register holds the base address of the vector table in ARM processors.

2. Step 2: Confirm other registers' roles

   PC controls instruction flow, LR stores return address, SP manages stack; none relocate vector table.

3. Final Answer:

   VTOR (Vector Table Offset Register) -> Option A

4. Quick Check:

   VTOR = vector table base register [OK]

Hint: VTOR register sets vector table base address [OK]

Common Mistakes:

• Confusing PC with VTOR
• Using LR or SP for vector table relocation
• Not knowing VTOR purpose

3. Given the following code snippet in ARM assembly, what is the effect of the instruction?
MOV R0, #0x20000000
STR R0, [VTOR]

medium

A. Enables interrupts globally

B. Resets the processor

C. Sets the vector table base address to 0x20000000

D. Clears the vector table

Solution

1. Step 1: Analyze MOV instruction

   MOV R0, #0x20000000 loads the address 0x20000000 into register R0.

2. Step 2: Analyze STR instruction

   STR R0, [VTOR] stores the value in R0 into the VTOR register, relocating the vector table base.

3. Final Answer:

   Sets the vector table base address to 0x20000000 -> Option C

4. Quick Check:

   STR to VTOR = relocate vector table base [OK]

Hint: STR to VTOR sets new vector table base address [OK]

Common Mistakes:

• Thinking it resets the processor
• Assuming it enables interrupts
• Believing it clears the vector table

4. A developer tries to relocate the vector table by writing to VTOR but the interrupts still point to the old addresses. What is the most likely cause?

medium

A. The stack pointer is incorrectly set

B. The processor clock is too slow

C. The interrupt handlers are missing

D. VTOR register is write-protected or not enabled for writing

Solution

1. Step 1: Understand VTOR write requirements

   VTOR may be write-protected or require special permissions to update its value.

2. Step 2: Check other options

   Clock speed or stack pointer issues do not affect vector table relocation; missing handlers cause faults but not relocation failure.

3. Final Answer:

   VTOR register is write-protected or not enabled for writing -> Option D

4. Quick Check:

   VTOR write protection blocks relocation [OK]

Hint: Check VTOR write permissions if relocation fails [OK]

Common Mistakes:

• Blaming clock speed for relocation issues
• Confusing stack pointer with vector table base
• Assuming missing handlers prevent relocation

5. In a system with multiple memory regions, how can vector table relocation improve system flexibility?

hard

A. By allowing the vector table to be moved to RAM for dynamic interrupt handler updates

B. By increasing the processor's clock frequency automatically

C. By disabling unused interrupts permanently

D. By encrypting the interrupt handlers for security

Solution

1. Step 1: Understand relocation benefits

   Relocating the vector table to RAM allows changing interrupt handlers at runtime, improving flexibility.

2. Step 2: Evaluate other options

   Clock frequency changes, disabling interrupts, or encryption are unrelated to vector table relocation.

3. Final Answer:

   By allowing the vector table to be moved to RAM for dynamic interrupt handler updates -> Option A

4. Quick Check:

   Relocation enables dynamic interrupt handler updates [OK]

Hint: Relocate vector table to RAM for flexible interrupt updates [OK]

Common Mistakes:

• Thinking relocation changes clock speed
• Assuming relocation disables interrupts
• Believing relocation encrypts handlers