1 Button debouncing library

button.c

/*
 * button.c
 *
 * Created: 18/11/2012 12:42:18 AM
 *  Author: MrTrick
 */

/************************************************************************/
/* SYSTEM INCLUDES                                                      */
/************************************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>

/************************************************************************/
/* PROJECTS INCLUDES                                                    */
/************************************************************************/
#include "button.h"
#include "gpio.h"

/************************************************************************/
/* CONFIGURATION/INITIALISATION                                         */
/************************************************************************/

//////////////////////////
// PIN
//////////////////////////

//PIN is D3, PCINT19
#define BUTTON_PIN				GPIO(D, 3, GPIO_DIR_IN, GPIO_INIT_PULLUP)
#define BUTTON_PIN_ACTIVE_LOW	true
#define BUTTON_PC_VECT			PCINT2_vect //for 16-23

/** 
 * Configure masks and interrupts
 */
inline void button_init_pin() {
	PCMSK2 |= (1<<PCINT19);	// Enable the PCINT19 mask
	PCICR |= (1<<PCIE2);	// Enable Pin change interrupt 2
	//(The associated flag is PCIFR.PCIF2)
}

//////////////////////////
// TIMING
//////////////////////////

//TCCR0B control values
#define BUTTON_TIMER_OFF ((0<<FOC0A)|(0<<FOC0B)|(0<<WGM02)|(0<<CS02)|(0<<CS01)|(0<<CS00)) //Timer stopped
#define BUTTON_TIMER_ON ((0<<FOC0A)|(0<<FOC0B)|(0<<WGM02)|(1<<CS02)|(0<<CS01)|(1<<CS00)) //Normal operation, with 1/1024 prescaling

#define BUTTON_CYCLES_HOLD		60 //Approx 2 seconds
#define BUTTON_CYCLES_REPEAT	20 //Approx 0.7 seconds

/**
 * Configure timer0
 */
inline void button_init_timer() {
	//Interrupts at 8MHz / 256 / 1024 = 32ms interrupt intervals
	// TCCR0A default, TCNT0 default (count register), OCR0x not used
	TCCR0B = BUTTON_TIMER_OFF; // The timer is initially off
	BIT_SET_HI(TIMSK0, TOIE0); // Enable the interrupt
}

/************************************************************************/
/* VARIABLES                                                            */
/************************************************************************/

/** 
 * Track the number of timer overflows; every 32ms 
 */
unsigned char button_cycle = 0;

/**
 * Store the last event 
 */
volatile unsigned char button_last_event = 0;

/************************************************************************/
/* LOCAL FUNCTIONS                                                      */
/************************************************************************/

/**
 * Check the pin state
 */
inline bool button_pin_pressed() {
	#if(BUTTON_PIN_ACTIVE_LOW)
		return gpio_pin_is_lo(BUTTON_PIN);
	#else
		return gpio_pin_is_hi(BUTTON_PIN);
	#endif;
}

/**
 * Reset and start the timer 
 */
inline void button_timer_start() { 
	TCNT0 = 0; 
	button_cycle = 0;
	TCCR0B = BUTTON_TIMER_ON; 
}

/** 
 * Stop the timer 
 */
inline void button_timer_stop() {
	TCCR0B = BUTTON_TIMER_OFF; 
}

/**
 * Check the timer state
 */
inline bool button_timer_running() {
	return !(TCCR0B == BUTTON_TIMER_OFF);
}	
	
/**
 * Interrupt handler - on pin change
 */	
ISR(BUTTON_PC_VECT) {
	//On pin press, start debouncing if not already
	if (button_pin_pressed() && !button_timer_running()) {
		button_timer_start();
	}
}

/**
 * Interrupt handler - on timer overflow (32ms)
 */
ISR(TIMER0_OVF_vect) {
	//Was the button released, or is it a false alarm?
	if (!button_pin_pressed()) {
		if (button_cycle > 0)
			button_last_event = BUTTON_EVENT_RELEASE;
		button_timer_stop();
		return;
	}
	
	//	
	switch (button_cycle++) {
		// Was the button just pressed?
		case 0: 
			button_last_event = BUTTON_EVENT_PRESS; 
		break;
		// Was the button held long enough?
		case BUTTON_CYCLES_HOLD:
			button_last_event = BUTTON_EVENT_HOLD;
		break;
		// Was it held that long, and then repeated?
		case BUTTON_CYCLES_HOLD + BUTTON_CYCLES_REPEAT:
			button_last_event = BUTTON_EVENT_REPEAT;
			button_cycle -= BUTTON_CYCLES_REPEAT; // Rewind so it will repeat again
		break;
	}
}


/************************************************************************/
/* GLOBAL FUNCTIONS                                                     */
/************************************************************************/

/**
 * Configure the button
 */
void button_init() {
	button_init_pin();
	button_init_timer();
}

/**
 * Fetch the last button event, and clear it.
 */
unsigned char button_read_event() {
	unsigned char event = button_last_event;
	button_last_event = BUTTON_EVENT_NONE;
	return event;
}

//////////////////////////////////////////////////////////////////////////

button.h

/*
 * button.h
 *
 * Created: 18/11/2012 12:42:01 AM
 *  Author: MrTrick
 */ 
#ifndef BUTTON_H_
#define BUTTON_H_

/************************************************************************/
/* CONSTANTS                                                            */
/************************************************************************/

#define BUTTON_EVENT_NONE		0
#define BUTTON_EVENT_PRESS		1<<0
#define BUTTON_EVENT_HOLD		1<<1
#define BUTTON_EVENT_REPEAT		1<<2
#define BUTTON_EVENT_RELEASE	1<<3

/************************************************************************/
/* GLOBAL FUNCTIONS                                                     */
/************************************************************************/

/**
 * Configure the button
 */
void button_init();

/**
 * Fetch the last button event, and clear it.
 */
unsigned char button_read_event();

#endif /* BUTTON_H_ */