AVRFreaks.net

  //PID routine

  Xk = adcout/KconRadByte;   //converting to Radians
  ADCSRA|=~(1<<ADSC)|(1<<ADATE); //Stop ADC after reading in the corresspondin position
 
  Ek= Wk-Xk;  //calc error
  sum = sum + Ek;  //adding the errors
  Pk= Kp*Ek; //prop error correction
  Ik= Ki*(sum);  //intergral error correction
  Dk= Kd*(Ek-Ekp);  //diff error correction
  Uk= (Pk+Ik+Dk);  //total correction
  Ekp= Ek;  //storing the present error value into another variable
  Ek=0;
 
  if (Uk<0)   //changin the direction signal
     PORTC = 0x00;
      else PORTC = 0xff;

  //End of routine

//PID-Controller
/* Table
*********************************************************    Tc=0.92s
Controller    Kp(*Kc)     Ti (*Tc)      Td (*Tc)
P            0.50         -                  -
PI           0.45        0.83                _
PID          0.60        0.50              0.125
**********************************************************
*/

#include <avr/io.h>
#include <avr/interrupt.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define SEI() asm volatile ("sei")
#define NOP() asm volatile ("nop")

#define reload 49535
#define prescaler0 1   //prescaler timer0
#define prescaler1 1   //prescaler timer1
#define AngReqd 90.0   //req posn
#define Wk 2.5   //=AngReqd*M_PI/180  ; reqd posn in rads
#define KconRadByte 81.169  //81.169 = 255/M_PI for conv to 8 bit value from radians
#define Kc 1.75       //Critical prop constant obtained using pcont for stable constant ossci.
#define Tsamp 0.001   //Tsamp=(65535-reload)*prescaler1/crystal.freq(=16 MHz)
#define Ti 0.46   
#define Td 0.115
#define Kp 1.05     
#define Ki 0.002283   //=Tsamp*Kp/Ti
#define Kd 120.75  //=Td*Kp/Tsamp

volatile unsigned int counter = 0;   // value to be written to OCRA
volatile unsigned int adcout = 0;    //value read from the ADC gives posn
volatile float Ekp=0;   //previous error
volatile float sum=0;   //sum
volatile  float Xk=0;   //present posn from adcout
volatile  float Ek=0;   //present posn
volatile  float Dk=0;   //diff error corrtn
volatile  float Ik=0;   //int error corrtn
volatile  float Pk=0;   //prop error corrtn
volatile  float Uk=0;   //net corrtn

int main(void)

{ 
   // Setup Timer1
   TCCR1A = 0;
   TCCR1B = (1<<CS00); // Prescale = 256 ;alternatively TCCR1B = prescaler1
    // note that the higher register is always written first
   TCNT1 = reload;
   TIMSK1 = (1<<TOIE1);

   // Setup timer0 WITH PWM,
   TCCR0A |= (1<<WGM00)|(1<<COM0A1)|(1<<CS00);
   // Write a proper value to the compare register
   OCR0A = counter; //initial setting is 0
   // output compare interrupt enabled
   TIMSK0 = (1<<OCIE0A);
   
   // Setup the ADC
   ADMUX = (1<<ADLAR);
   //ADCSRB = (1<<ADTS2)|(1<<ADTS1);
   ADCSRA = (1<<ADEN)|(1<<ADIE)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0); //not started yet
   
   // Set the B-Pins to OUTPUT (since OC1A is located at PB7)
   DDRB = 0xff;
   DDRD = 0x00;
   DDRC = 0xff;
   DDRE = 0xff;   
   DDRA = 0xff;
   PORTA = 0xff;
   PORTC = 0xff;
   PORTE = 0xff;
   //enable all interrupts
   SEI();

  while (1)  //endless loop
  {}

   return 0;
}

//Timer 1 overflow
ISR (TIMER1_OVF_vect)
{ 
    TCNT1 = reload;

   ADCSRA|= (1<<ADSC)|(1<<ADATE);//Start ADC
   //It doesnt seem like a wait routine is required for the completion of ADC conversion
    short int i=0;
   while(i<18)
    {
       NOP();
      i++;
    }
 
  //to chk the frequency of the loop
  int temp=0;
  temp= PORTA;
  PORTA=255-temp;

  //PID routine

  Xk = adcout/KconRadByte;
  ADCSRA|=~(1<<ADSC)|(1<<ADATE); //Stop ADC after reading in the corresspondin position
  Ek= Wk-Xk;
  sum = sum + Ek;  //adding the errors
  Pk= Kp*Ek; //prop error correction
  Ik= Ki*(sum);  //intergral error correction
  Dk= Kd*(Ek-Ekp);  //diff error correction
  Uk= (Pk+Ik+Dk);  //total correction
  Ekp= Ek;  //storing the present error value into another variable
  Ek=0;
 
  if (Uk<0)   //changin the direction signal
   {
     PORTC = 0x00;
   }
   else PORTC = 0xff;

  //End of routine
   counter = fabs(KconRadByte*Uk); //value betn 0 and 255 for the PWM compare reg
}

//Timer 0 PWM
ISR (TIMER0_COMP_vect)
{
  OCR0A = counter;
}

//ADC
ISR (ADC_vect)
{
  adcout = ADCH ;
}