Interrupt Vector Table in Embedded C: What It Is and How It Works

An interrupt vector table in Embedded C is a special list of addresses that tells the microcontroller where to find the code to run when an interrupt happens. Each entry in this table points to an interrupt service routine (ISR), which handles specific events like timers or input signals.

How It Works

Think of the interrupt vector table as a phone book for your microcontroller. When an interrupt occurs, the microcontroller looks up the interrupt number in this table to find the address of the function that should run. This function is called an Interrupt Service Routine (ISR).

Imagine you have different emergency contacts saved in your phone for fire, police, or medical help. Similarly, the interrupt vector table stores addresses for different ISRs, so the microcontroller quickly knows who to call when something important happens.

This system allows the microcontroller to pause its current task and respond immediately to urgent events, making embedded systems responsive and efficient.

Example

This example shows a simple interrupt vector table setup for a microcontroller using Embedded C. It links an interrupt to its handler function.

c

#include <stdint.h>

// Define a type for ISR pointers
typedef void (*ISR)(void);

// Example ISR function
void Timer_ISR(void) {
    // Code to handle timer interrupt
}

// Interrupt vector table placed at a specific memory location
__attribute__((section(".isr_vector")))
ISR interrupt_vector_table[] = {
    (ISR)0,          // Reset vector (usually initial stack pointer)
    Timer_ISR,  // Timer interrupt handler
    (ISR)0           // Other interrupts can be added here
};

int main(void) {
    // Main program loop
    while(1) {
        // Normal code execution
    }
    return 0;
}

When to Use

You use an interrupt vector table in embedded systems programming whenever your microcontroller needs to respond quickly to external or internal events without waiting for the main program to check for them. This is common in real-time systems like:

• Handling button presses or sensor signals
• Managing timers for precise time control
• Communicating with other devices via serial ports
• Responding to hardware faults or errors

Using interrupts and the vector table helps keep your program efficient and responsive, especially when multiple events can happen at once.

Key Points

• The interrupt vector table stores addresses of interrupt handlers (ISRs).
• It allows the microcontroller to quickly jump to the correct code when an interrupt occurs.
• Each interrupt source has a unique position in the table.
• Proper setup of the vector table is essential for reliable interrupt handling.
• Interrupts improve responsiveness and efficiency in embedded systems.

Key Takeaways

The interrupt vector table maps interrupts to their handler functions in embedded C.

It enables fast and organized responses to hardware or software events.

Each interrupt has a unique entry pointing to its Interrupt Service Routine.

Using interrupts improves system responsiveness without constant polling.

Correct vector table setup is crucial for stable embedded system behavior.