Interrupt vector table in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this interrupt vector table initialization?

Consider this embedded C code snippet initializing an interrupt vector table. What will be the output when the reset_handler is called?

Embedded C

#include <stdio.h>

void reset_handler() {
    printf("System Reset\n");
}

void nmi_handler() {
    printf("NMI Interrupt\n");
}

void (* const interrupt_vector_table[])(void) = {
    reset_handler,  // Reset vector
    nmi_handler     // NMI vector
};

int main() {
    interrupt_vector_table[0]();
    return 0;
}

A NMI Interrupt

B Runtime error: segmentation fault

C System Reset

D Compilation error due to missing semicolon

💡 Hint

Look at which function is called from the vector table index 0.

The first element in the interrupt vector table is reset_handler. Calling interrupt_vector_table[0]() executes reset_handler, which prints "System Reset".

🧠 Conceptual

intermediate

Which statement correctly describes the interrupt vector table?

Choose the correct description of an interrupt vector table in embedded systems.

A It stores addresses of interrupt service routines and is used by the processor to jump to the correct handler.

B It is a table that holds the priority levels of interrupts but not their addresses.

C It is a memory area where all interrupt data is stored during execution.

D It is a list of all interrupts that have occurred since system start.

💡 Hint

Think about what the processor needs to do when an interrupt occurs.

The interrupt vector table contains the addresses of interrupt service routines (ISRs). When an interrupt occurs, the processor uses this table to find and jump to the correct ISR.

🔧 Debug

advanced

What error occurs in this interrupt vector table declaration?

Examine the following code snippet. What error will occur when compiling?

Embedded C

void reset_handler(void) {}
void nmi_handler(void) {}

void (*interrupt_vector_table[])(void) = {
    reset_handler,
    nmi_handler,
};

A Error: incompatible types in assignment to function pointer array.

B Error: missing 'const' qualifier for the vector table pointer.

C Error: trailing comma in the initializer list is not allowed in C.

D No error; code compiles successfully.

💡 Hint

Check if trailing commas are allowed in array initializers in C.

In C, trailing commas in array initializers are allowed. The code declares an array of function pointers correctly and compiles without error.

❓ Predict Output

advanced

What is the output of this vector table with a default handler?

Given this embedded C code with a default interrupt handler, what will be printed when interrupt_vector_table[2]() is called?

Embedded C

#include <stdio.h>

void reset_handler() {
    printf("Reset Handler\n");
}

void default_handler() {
    printf("Default Interrupt Handler\n");
}

void (* const interrupt_vector_table[])(void) = {
    reset_handler,
    default_handler,
    default_handler
};

int main() {
    interrupt_vector_table[2]();
    return 0;
}

A Reset Handler

B Default Interrupt Handler

C Segmentation fault at runtime

D Compilation error: initializer list size mismatch

💡 Hint

Look at the function pointer at index 2 in the vector table.

The third element (index 2) in the vector table points to default_handler, which prints "Default Interrupt Handler".

🚀 Application

expert

How many entries are in this interrupt vector table array?

Given this embedded C code snippet, how many entries does the interrupt_vector_table array contain?

Embedded C

void reset_handler(void) {}
void nmi_handler(void) {}
void hard_fault_handler(void) {}

void (* const interrupt_vector_table[])(void) = {
    reset_handler,
    nmi_handler,
    hard_fault_handler
};

A 3

B 2

C 4

D 1

💡 Hint

Count the number of functions listed inside the initializer braces.

The array is initialized with three function pointers: reset_handler, nmi_handler, and hard_fault_handler. So, it contains 3 entries.