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I am actually working on a small project using an Arduino micro-controller ATMEGA 328. Timing issues are very critical so I had to find a way to use timer interrupts.

Arduino, Allegro 5804 and stepper motor

I found the following code and adapted it to the ATMEGA 328.
http://gonium.net/md/2006/12/27/i-will-think-before-i-code/

Following is my implementation for the ATMEGA 328 … The code is driving a stepper motor through the Allegro 5804 stepper motor driver.

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

#define INIT_TIMER_COUNT 6
#define RESET_TIMER2 TCNT2 = INIT_TIMER_COUNT

#define CW     HIGH
#define CCW    LOW

// One and two phases
// 60000ms / 48steps = 1250ms/step
#define TRACK  1250

// Half steps
// 60000ms / 96steps = 625
//#define TRACK 625

int led13 = HIGH;
long counter = 0;
int stepStack = 0;

// Aruino runs at 16 Mhz, so we have 1000 Overflows per second...
// 1/ ((16000000 / 64) / 256) = 1 / 1000
ISR(TIMER2_OVF_vect) {
  RESET_TIMER2;
  counter++;
  if(!(counter%TRACK))
  {
    // enqueue step message
    stepStack++;
  }
};

void setup()
{
  pinMode(2, OUTPUT);  // Step
  pinMode(3, OUTPUT);  // Direction
  pinMode(13, OUTPUT); // LED

  pinMode(4, INPUT);   // Power on/off
  pinMode(5, INPUT);   // Rewind

  //Timer2 Settings: Timer Prescaler /64,
  TCCR2A |= (1<<CS22);
  TCCR2A &= ~((1<<CS21) | (1<<CS20));
  // Use normal mode
  TCCR2A &= ~((1<<WGM21) | (1<<WGM20));
  // Use internal clock - external clock not used in Arduino
  ASSR |= (0<<AS2);
  //Timer2 Overflow Interrupt Enable
  TIMSK2 |= (1<<TOIE2) | (0<<OCIE2A);
  RESET_TIMER2;
  sei();
}

void loop()
{
  // READ INPUTS
  int fast = digitalRead(4);
  int rewind = digitalRead(5);

  if(rewind == HIGH || fast == HIGH)
  {
    // Toggle the LED
    led13 ^= 1;
    digitalWrite(13, led13);

    // Clear the step messages buffer
    stepStack = 0;

    // Set rewind direction
    if(rewind == HIGH)
      digitalWrite(3, CCW);
    else
      digitalWrite(3, CW);

    digitalWrite(2, HIGH);
    delay(10);  

    digitalWrite(2, LOW);
    delay(10);
  }
  else if(stepStack)
  {
    // Toggle the LED
    led13 ^= 1;
    digitalWrite(13, led13); 

    // Set tracking direction
    digitalWrite(3, CW);

    digitalWrite(2, HIGH);
    delay(1);  

    digitalWrite(2, LOW);
    delay(1);

    stepStack--;
  }
}