Vector table structure in ARM Architecture - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the first entry in the ARM vector table.

ARM Architecture

The first entry in the vector table is the initial [1] value.

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Astatus register

Bprogram counter

Cstack pointer

Dlink register

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing the first entry with the reset handler address.

Thinking the program counter is the first entry.

The ARM vector table starts with the initial stack pointer value, which sets up the stack before execution begins.

2fill in blank

medium

Complete the code to identify the second entry in the ARM vector table.

ARM Architecture

The second entry in the vector table holds the address of the [1] handler.

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Afault

Binterrupt

Cexception

Dreset

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing reset handler with interrupt handler.

Assuming the first entry is the reset handler.

The second entry is the reset handler address, which is the starting point of program execution after reset.

3fill in blank

hard

Fix the error in the description of the vector table entries.

ARM Architecture

The vector table entries are located at address [1] in memory.

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A0x00000000

B0x10000000

C0x20000000

D0xFFFFFFFF

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming vector table is at a high memory address.

Confusing vector table location with stack location.

The ARM vector table is located at the start of memory, address 0x00000000, by default.

4fill in blank

hard

Fill both blanks to describe the vector table entries for exceptions and interrupts.

ARM Architecture

Entries after the reset handler include [1] and [2] vectors.

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ANMI

Bstack pointer

CIRQ

Dprogram counter

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up stack pointer with interrupt vectors.

Confusing program counter with vector entries.

After the reset handler, the vector table includes the Non-Maskable Interrupt (NMI) and Interrupt Request (IRQ) vectors.

5fill in blank

hard

Fill all three blanks to complete the vector table entry description.

ARM Architecture

The vector table is an array of [1]-bit addresses starting at [2], with the first entry as the [3] pointer.

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A32

B0x00000000

Cinitial stack

D16

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming 16-bit addresses in the vector table.

Confusing the initial stack pointer with the program counter.

The ARM vector table consists of 32-bit addresses starting at address 0x00000000, with the first entry holding the initial stack pointer.

Practice

1. What is the first entry in the ARM vector table?

easy

A. Program counter start address

B. Reset handler address

C. Initial stack pointer address

D. Interrupt service routine address

Solution

1. Step 1: Understand vector table structure

   The ARM vector table begins with the initial stack pointer value to set up the stack.

2. Step 2: Identify the first entry

   The first entry is the initial stack pointer address, followed by the reset handler address.

3. Final Answer:

   Initial stack pointer address -> Option C

4. Quick Check:

   First entry = Initial stack pointer address [OK]

Hint: Remember: stack pointer comes before reset handler [OK]

Common Mistakes:

• Confusing reset handler as first entry
• Thinking program counter is first
• Assuming interrupt routine is first

2. Which of the following correctly describes the second entry in the ARM vector table?

easy

A. Reset handler address

B. Initial stack pointer address

C. Undefined instruction handler

D. Non-maskable interrupt handler

Solution

1. Step 1: Recall vector table order

   The first entry is the initial stack pointer, so the second entry is the reset handler.

2. Step 2: Confirm second entry role

   The reset handler is the address where the processor starts executing after reset.

3. Final Answer:

   Reset handler address -> Option A

4. Quick Check:

   Second entry = Reset handler address [OK]

Hint: Second entry always points to reset handler [OK]

Common Mistakes:

• Mixing up with interrupt handlers
• Choosing stack pointer again
• Confusing with exception handlers

3. Given the following vector table snippet:

0x00000000: 0x20001000  (Initial SP)
0x00000004: 0x00001005  (Reset Handler)
0x00000008: 0x00001010  (NMI Handler)
0x0000000C: 0x00001020  (HardFault Handler)

Which address will the processor jump to on a HardFault exception?

medium

A. 0x20001000

B. 0x00001005

C. 0x00001010

D. 0x00001020

Solution

1. Step 1: Locate HardFault entry in vector table

   The HardFault handler address is at offset 0x0C in the vector table.

2. Step 2: Identify the address at 0x0000000C

   The address at 0x0000000C is 0x00001020, which is the HardFault handler.

3. Final Answer:

   0x00001020 -> Option D

4. Quick Check:

   HardFault handler = 0x00001020 [OK]

Hint: Match exception to its vector table offset [OK]

Common Mistakes:

• Choosing reset handler address
• Confusing NMI and HardFault handlers
• Selecting initial stack pointer

4. A developer sets the vector table's first entry to 0x00000000 instead of the initial stack pointer. What issue will most likely occur?

medium

A. Stack pointer will be invalid causing a crash

B. Processor will reset normally

C. Reset handler will not execute

D. Interrupts will be ignored

Solution

1. Step 1: Understand role of first vector entry

   The first entry sets the initial stack pointer address for the processor.

2. Step 2: Analyze effect of setting it to zero

   Setting it to 0x00000000 means the stack pointer points to an invalid memory location, causing a crash.

3. Final Answer:

   Stack pointer will be invalid causing a crash -> Option A

4. Quick Check:

   Invalid stack pointer = Crash [OK]

Hint: First vector must be valid stack pointer [OK]

Common Mistakes:

• Thinking reset handler won't run
• Assuming interrupts are disabled
• Believing processor resets normally

5. You want to add a custom interrupt handler for a new peripheral. Where in the ARM vector table should you place this handler's address?

hard

A. At the first entry replacing the initial stack pointer

B. At the specific interrupt vector slot assigned to that peripheral

C. At the second entry replacing the reset handler

D. At the end of the vector table after all default handlers

Solution

1. Step 1: Understand vector table layout

   The vector table has fixed slots for each exception and interrupt type.

2. Step 2: Identify correct slot for custom interrupt

   Custom peripheral interrupts must be placed at their assigned interrupt vector slot, not at stack pointer or reset handler entries.

3. Final Answer:

   At the specific interrupt vector slot assigned to that peripheral -> Option B

4. Quick Check:

   Custom handler = Assigned interrupt vector slot [OK]

Hint: Place handlers in their assigned vector slots only [OK]

Common Mistakes:

• Replacing stack pointer or reset handler
• Appending handler at vector table end
• Ignoring fixed vector slot assignments