Vector table structure in ARM Architecture - Mini Project: Build & Apply

Understanding Vector Table Structure in ARM Architecture

📖 Scenario: You are learning about how ARM processors handle interrupts and exceptions. The vector table is a key part of this process. It is a table of addresses that the processor uses to find the code to run when an interrupt or exception occurs.Imagine the vector table as a list of emergency phone numbers. Each number corresponds to a specific emergency type. When an emergency happens, you look up the right number and call it.

🎯 Goal: Build a simple representation of the ARM vector table structure. You will create a list of vector entries with their exact addresses and names. Then, you will add a configuration variable for the base address of the vector table. Next, you will write code to access the vector table entries. Finally, you will complete the structure by adding the total number of vectors.

📋 What You'll Learn

Create a list called vector_table with exact vector names and addresses

Add a variable base_address with the exact value 0x00000000

Use a loop to create a dictionary vectors mapping vector names to their addresses

Add a variable vector_count with the exact number of vectors in the table

💡 Why This Matters

🌍 Real World

Understanding the vector table structure helps in embedded systems programming and debugging ARM-based microcontrollers and processors.

💼 Career

Knowledge of vector tables is essential for firmware developers, embedded systems engineers, and anyone working with low-level ARM architecture programming.

1

Create the vector table list

Create a list called vector_table with these exact tuples: ("Reset", 0x00000000), ("Undefined Instruction", 0x00000004), ("Software Interrupt", 0x00000008), ("Prefetch Abort", 0x0000000C), ("Data Abort", 0x00000010), ("Reserved", 0x00000014), ("IRQ", 0x00000018), ("FIQ", 0x0000001C)

ARM Architecture

# Create the vector_table list with exact vector names and addresses
# Your code here

Hint

Use a Python list with tuples. Each tuple has the vector name as a string and the address as a hex number.

2

Add the base address variable

Add a variable called base_address and set it to the exact value 0x00000000

ARM Architecture

vector_table = [
    ("Reset", 0x00000000),
    ("Undefined Instruction", 0x00000004),
    ("Software Interrupt", 0x00000008),
    ("Prefetch Abort", 0x0000000C),
    ("Data Abort", 0x00000010),
    ("Reserved", 0x00000014),
    ("IRQ", 0x00000018),
    ("FIQ", 0x0000001C)
]

# Add the base_address variable here
# Your code here

Hint

Use a simple variable assignment with the exact hex value.

3

Create a dictionary mapping vector names to addresses

Use a for loop with variables name and address to iterate over vector_table. Inside the loop, add entries to a dictionary called vectors that maps each name to its address

ARM Architecture

vector_table = [
    ("Reset", 0x00000000),
    ("Undefined Instruction", 0x00000004),
    ("Software Interrupt", 0x00000008),
    ("Prefetch Abort", 0x0000000C),
    ("Data Abort", 0x00000010),
    ("Reserved", 0x00000014),
    ("IRQ", 0x00000018),
    ("FIQ", 0x0000001C)
]

base_address = 0x00000000

# Create the vectors dictionary using a for loop
# Your code here

Hint

Start with an empty dictionary. Use a for loop to add each vector name and address.

4

Add the vector count variable

Add a variable called vector_count and set it to the exact length of vector_table using the len() function

ARM Architecture

vector_table = [
    ("Reset", 0x00000000),
    ("Undefined Instruction", 0x00000004),
    ("Software Interrupt", 0x00000008),
    ("Prefetch Abort", 0x0000000C),
    ("Data Abort", 0x00000010),
    ("Reserved", 0x00000014),
    ("IRQ", 0x00000018),
    ("FIQ", 0x0000001C)
]

base_address = 0x00000000

vectors = {}
for name, address in vector_table:
    vectors[name] = address

# Add the vector_count variable here
# Your code here

Hint

Use the len() function to get the number of vectors in the list.

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