AVR Timer Interrupt Examples

interrupt_example.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdbool.h>

/*
 * A global flag used to communicate between the Interrupt Service Routine
 * and the main program.  It has to be declared volatile or the compiler
 *  might optimize it out.
 */
volatile bool update = false;

/*
 * The interrupt service routine.  This is run whenever the interrupt
 * "TIMER1_OVF_vect" is triggered.  This is an interrupt that the ATmega328P
 * triggers whenever Timer 1 overflows past its maximum value.  It sets
 * the update flag to "true" to tell the main program that it needs to
 * do something.
 */
ISR(TIMER1_OVF_vect) {
	update = true;
}

int main(void) {

	// Set PORTB pins as output, but off
	DDRB = 0xFF;
	PORTB = 0x00;

	// Turn on timer with no prescaler on the clock for fastest
	// triggering of the interrupt service routine.
	TCCR1B |= _BV(CS10);
	TIMSK1 |= _BV(TOIE1);

	// Turn interrupts on.
	sei();

	for(;;) {

		// This turns interrupts off for the code inside it.  Probably
		// not needed here but it's good to know about.
		ATOMIC_BLOCK(ATOMIC_FORCEON) {

			// If the ISR has indicated we need to update the state
			// then run this block.
			if (update) {

				// Toggle the pins on PORTB on/off.
				PORTB ^= 0xFF;	// Toggle the pins on/off

				/*
				 * We reset the update flag to false to indicate that
				 * we are done.  This ensures that this block will not
				 * be executed until update is set to true again, which
				 * is only done by the interrupt service routine.
				 */
				update = false;
			}
		}

	}

}

timer_button_read.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/atomic.h>
#include <stdbool.h>
#include <util/delay.h>

/*
 * Struct to hold the old and new pin states;
 */
volatile struct {
	uint8_t d_old;
	uint8_t d;
} pins;

/*
 * Change the current pin state to the old pin state and read the new pin
 * state. 
 */
ISR(TIMER1_OVF_vect) {
	pins.d_old = pins.d;
	pins.d = PIND;
}

int main(void) {

	DDRB = 0x01;
	PORTD = 0x04; // pullup on PD2

	// Turn on timer with no prescaler on the clock for fastest
	// triggering of the interrupt service routine.
	TCCR1B |= _BV(CS10);
	TIMSK1 |= _BV(TOIE1);

	// Turn interrupts on.
	sei();

	for(;;) {

		ATOMIC_BLOCK(ATOMIC_FORCEON) {
			// Toggle pin state on low edge (pull-up on PD2 means the pin is active low)
			if ( !(pins.d & _BV(PD2)) && (pins.d_old & _BV(PD2)) )  {
				PORTB ^= _BV(PB0);
				_delay_ms(10);
			}

		}

	}

}

timer_button_read_tiny85.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/atomic.h>
#include <stdbool.h>
#include <util/delay.h>

/*
 * Struct to hold the old and new pin states;
 */
volatile struct {
	uint8_t b_old;
	uint8_t b;
} pins;

/*
 * Change the current pin state to the old pin state and read the new pin
 * state. 
 */
ISR(TIM0_OVF_vect) {
	pins.b_old = pins.b;
	pins.b = PINB;
}

int main(void) {

	DDRB = 0b011110; // PB1 through PB4 as outputs
	PORTB = 0b000001; // pullup on PB0 as an input

	// Turn on timer with no prescaler on the clock for fastest
	// triggering of the interrupt service routine.
	TCCR0B |= _BV(CS00);
	TIMSK |= _BV(TOIE0);

	// Turn interrupts on.
	sei();

	for(;;) {

		ATOMIC_BLOCK(ATOMIC_FORCEON) {
			// Toggle pin state on low edge (pull-up on PB0 means the pin is active low)
			if ( !(pins.b & _BV(PB0)) && (pins.b_old & _BV(PB0)) )  {
				if (PORTB & _BV(PB1))
					PORTB &= ~_BV(PB1);
				else
					PORTB |= _BV(PB1);
				_delay_ms(10);
			}

		}

	}

}

Thank you very much this piece of code help me understand the concept.

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