gpio-interrupt - C routine for handling interrupts generated on GPIO

gpio-interrupt.c

/* Demonstration C GPIO interrupt handling routine for Raspberry Pi

This is a modified code found at https://github.com/phil-lavin/raspberry-pi-gpio-interrupt

The program displays a notice whenever you:
  -turn on the Raspberry Pi's pin 11 (apply 3.3V),
  -turn the pin off.

This routine uses wiringPi library (follow the installation instructions at wiringpi.com),
and should be compiled with a command:

gcc source_filename -o executable_filename -lwiringPi

You must have root privileges to run it - I don't know any workaround yet:

sudo ./executable_filename

Then the program displays a notice whenever you turn the GPIO pin 11 on and off.
It runs as an infinite loop and you can cancel it by pressing ctrl-C.
*/

#include <stdio.h>
#include <sys/time.h>
#include <wiringPi.h>

// Which GPIO pin we're using. For this program we'll use physical pin numbers.
#define PIN 11

// How much time a change must be since the last in order to count as a change
// (in microseconds); allows to avoid generating interrupts on contact bouncing etc.
#define IGNORE_CHANGE_BELOW_USEC 10000

// Current state of the pin
static volatile int state;

// Time of last change
struct timeval last_change;

// Handler for interrupt
void handle(void) {
	struct timeval now;
	unsigned long diff;

	gettimeofday(&now, NULL);

	// Time difference in microseconds
	diff = (now.tv_sec * 1000000 + now.tv_usec) - (last_change.tv_sec * 1000000 + last_change.tv_usec);

	// Filter any changes in intervals shorter than diff (like contact bouncing etc.):
	if (diff > IGNORE_CHANGE_BELOW_USEC) {

                // Check whether the last state was on or off:
		if (state) {
                        // Print info to console:
			printf("Input goes off\n");
                        // You can add some code to do when input goes off here...
		}
		else {
			// Print info to console:
                        printf("Input goes on\n");
                        // Add code to do when input goes on here...
		}

		// Change the "state" variable value:
                state = !state;
	}
        // Store the time for last state change:
	last_change = now;
}

int main(void) {
	// Init  -- use the physical pin number on RPi P1 connector
	wiringPiSetupPhys();

	// Set pin to input in case it's not
	pinMode(PIN, INPUT);

	// Time now
	gettimeofday(&last_change, NULL);

	// Bind to interrupt
	wiringPiISR(PIN, INT_EDGE_BOTH, &handle);

	// Get initial state of pin
	state = digitalRead(PIN);

        // Feedback for user that the program has started, depending on input state:
	if (state) {
		printf("Started! Initial state is on\n");
	}
	else {
		printf("Started! Initial state is off\n");
	}

	// Waste time but not CPU
	for (;;) {
		sleep(1);
	}
}

Sorry maybe I got it wrong, but why do I have to set OUTPUT @ line 76? I would have expected "INPUT". OK, it works, but I do not understand.

Sorry maybe I got it wrong, but why do I have to set OUTPUT @ line 76? I would have expected "INPUT". OK, it works, but I do not understand.

Must have been just a brain fart on my part... Thanks for noticing :)

};-)