C Interrupts

C interrupts

Created By: chatGPT

In C programming, interrupts are signals that inform the processor to stop its current activities and execute a specific piece of code, known as an interrupt service routine (ISR). Interrupts are crucial for real-time computing, allowing the system to respond promptly to events.

// Example of a simple ISR in C
#include <avr/io.h>
#include <avr/interrupt.h>

ISR(INT0_vect) {
    // Code to execute when interrupt occurs
    PORTB ^= (1 << PB0); // Toggle an LED connected to PB0
}

You can configure interrupts to be triggered by different events, such as pin changes, timers, or communication protocols. To use interrupts effectively, follow these steps:

// Configuration for External Interrupt in AVR
void setup() {
    // Set up the pin as input
    DDRD &= ~(1 << DDD2); // PD2 as input (INT0)

    // Enable external interrupt INT0
    EIMSK |= (1 << INT0);

    // Trigger on falling edge
    EICRA |= (1 << ISC01);
    EICRA &= ~(1 << ISC00);

    // Enable global interrupts
    sei();
}

When an interrupt occurs, the microcontroller will save the context of the main program and transfer control to the ISR. After executing the ISR, control returns to the point where the interrupted code was running.

// Main loop example with enabled interrupt
int main() {
    setup();
    while (1) {
        // Main program code
        // Do something useful
    }
}

When dealing with interrupts, be mindful of the critical sections. This is the part of the code where shared resources may be modified. If an interrupt occurs during this section, it could lead to inconsistent or corrupted data. You can use mechanisms to temporarily disable interrupts when entering critical sections.

// Critical section example
void critical_function() {
    cli(); // Disable interrupts
    // Modify shared variables safely
    sei(); // Re-enable interrupts
}

In summary, interrupts provide a mechanism for a program to respond to asynchronous events, making them essential in embedded systems. Always remember to keep your ISR short and efficient since a long ISR can disrupt the flow of your program, potentially missing subsequent interrupts.

// Example of a short ISR
ISR(TIMER1_COMPA_vect) {
    // Minimal code for timer interrupt
    // Just set a flag or increment a counter
    tick_count++;
}