How can I create interrupts in C for Arduino? - c

Question

So I did this code for Arduino in C. It is for controlling a stepper motor. But every time I have to wait until the microcontroller begins a new loop so that it can take the value for the new variables, how can I create an interrupt so it will do it in any time of the program?
#include <avr/io.h>
#define F_CPU 4000000UL
#include <util/delay.h>
#include "IO/ioconfig.h"
#include "leebotones/leebotonesA.h"
#include "leebotones/leebotonesB.h"
#include "rutina/avanza.h"
#include "rutina/retrocede.h"
char variableA = 0;
char variableB = 0;
int main(void){
ioconfig();
while(1) {
if (leebotonesA()==1) {
variableA++;
} //Fin de if leebotonesA.
if (leebotonesB()==1) {
if (variableA==0) {
variableB=1;
}
else {
variableB=0;
}
}
if (variableA==2) {
variableA=0;
PORTD=0x00;
_delay_ms(10000);
} //Fin de if variableA.
if (variableA==1 && variableB==0) {
avanza();
} //Fin de if leebotonesA.
if (variableA==1 && variableB==1) {
retrocede();
}
_delay_ms(25);
}//End of while
}// End of main

Answer 1

A hardware interrupt on the Arduino occurs when one of the interrupt pins receives a change of state. The function to use, if you have access to the Arduino library, is attachInterrupt.
Example code to listen for an interrupt (derived from the documentation I linked to, I added comments to help explain):
// The Arduino has an LED configured at pin 13
int pin = 13;
// Holds the current state of the LED to handle toggling
volatile int state = LOW;
void setup()
{
pinMode(pin, OUTPUT);
// First Parameter:
// 0 references the interrupt number. On the Duemilanove, interrupt 0
// corresponds to digital pin 2 and interrupt 1 corresponds to digital pin
// 3. There are only two interrupt pins for the Duemilanove and I believe
// the Uno too.
// Second Parameter:
// blink is the name of the function to call when an interrupt is detected
// Third Parameter:
// CHANGE is the event that occurs on that pin. CHANGE implies the pin
// changed values. There is also LOW, RISING, and FALLING.
attachInterrupt(0, blink, CHANGE);
}
void loop()
{
// Turns the LED on or off depending on the state
digitalWrite(pin, state);
}
void blink()
{
// Toggles the state
state = !state;
}
There is also a concept of Pin Change Interrupts that is supported on every pin. See the bottom part of introduction to interrupts for more info.
However, sometimes a hardware interrupt can be avoided by refactoring your code. For example, keep your loop() running quickly --- mostly just reading inputs, limit the use of delay() --- and in the loop, call a function when the targeted inputted value is detected.

Answer 2

MSTimer2 is an Arduino library function to let you set timer interrupts.
Another alternative to delay, rather than interrupts, is to set a timer and check it each time through the loop. http://arduino.cc/en/Tutorial/BlinkWithoutDelay explains the concepts. The Metro library http://arduino.cc/playground/Code/Metro implements this and is easy to use. I've used it instead of delay() so that I can check for a button push while my robot is moving.