AVRFreaks.net

/*
* ----------------------------------------------------------------------------
* "THE BEER-WARE LICENSE" (Revision 42):
* <joerg@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
* can do whatever you want with this stuff. If we meet some day, and you think
* this stuff is worth it, you can buy me a beer in return.        Joerg Wunsch
* ----------------------------------------------------------------------------
*
* Simple AVR demonstration.  Controls a LED that can be directly
* connected from OC1/OC1A (this is PB5 on mega128) to GND.  The brightness of the LED is
* controlled with the PWM.  After each period of the PWM, the PWM
* value is either incremented or decremented, that's all.
*
* $Id: demo.c,v 1.6.2.3 2006/01/05 21:33:08 joerg_wunsch Exp $
*/

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

char st = 0x00;// THIS IS A FLAG SO THAT PWM VALUE IS NOT REASSIGNED BEFORE BEING USED
int PWM = 0x0200;

ISR (TIMER1_OVF_vect)      // timer1 overflow interrupt
{
   /* on the atmega128, the clocksource for timer1 (TCCR1B) is set to use the full clock,
   * in my case 16MHz. As a 10-bit timer, this interrupt should fire
   * every (2^10) / 16000000 = 0.064 milliseconds (I think).
   * Therefore, the LED should "ramp" from 0 to full in
   * 0.064 * (2^10) = roughly 65.5 milliseconds.*/
   
    OCR1A = PWM;                  //because this is an interrupt routine, it is safe to use 16-bit assignment.
   st=0x00;  // PWM VARIABLE CAN ACCEPT NEW VALUE
}

void ioinit (void)         //initialize pwm and enable interrupts.
{
   
   TCCR1B |= ((1 << CS10) | ( 0 <<CS11));           // full XTAL, no prescalar
   TCCR1A |= ((1 << WGM10) | (1 << WGM11));
    TCCR1A |= (1 << COM1A1);            //Clear OC1A on compare match when up-counting, set OC1A on compare match when down-counting.
    OCR1A = 0;
    DDRD = _BV (PD5);   //0x20

   // Enable timer 1 overflow interrupt.
   TIMSK = _BV (TOIE1);

   //enable global interrupts
   sei ();
}



int main (void)
{
   
    DDRD |= (0<<DDD2);    //prepare portD.2 for read with internal pull ups
    PORTD |= (1<<PORTD2);
    ioinit (); //set up pwm

   // loop forever, the interrupts are doing the rest

   while(1)
   {
   if (!(PIND & (1<<PD2))) //READ STATE ON PIND.2 CHECK FOR 0
   {
      if (st==0x00)
      {
         if (--PWM==0)
         {
            PWM=1;
            
         }
         st=0x01;  // PREVENT PWM VARIABLE FROM CHANGING UNTILL OCR1A IS ASSINGED PWM
      }
   }      
   else
   {
      if (st==0x00)
      {
         if (++PWM==0X3FF)
         {
            PWM--;
            
         }
         st=0x01;
         
      }
      
   }

   }
}