While loop execution time

[gehan_s]

Hi all,

How can I determine the total runtime of this while(1) loop? The microcontroller is a 16F877A and has a oscillator frequency of 20MHz.

Thanks in advance !!!!!!!!!!!!!!!

void main(){

     float error   = 0;   // present error
     float error_1 = 0;   // previous error
     float acc_err = 0;   // accumulated error
     float vout    = 0;   // actual O/P value
     float set     = 0;   // set O/P value
     float pwm     = 0;
     float Kp      = 0;
     float Ki      = 0;
     float Kd      = 0;
     float T       = 0;   // time between two samples
     char txt1[5];
     char txt2[5];
     
     TRISB         = 0;

     Lcd_Init(&PORTB);
     Pwm_Init(10000);
     Pwm_Start();
     Pwm_Change_Duty(pwm);
     Lcd_Cmd(LCD_CURSOR_OFF);
     Lcd_Cmd(LCD_CLEAR);

     delay_ms(10);

     while(1){
     
          set     = Adc_Read(1);
          Kp      = Adc_Read(2);
          Ki      = Adc_Read(3);
          Kd      = Adc_Read(4);
          vout    = Adc_Read(0);
          set     = (set/1024)*5;
          Kp      = (Kp/1024)*100;
          Ki      = (Ki/1024)*100;
          Kd      = (Kd/1024)*100;
          vout    = (vout/1024)*5;
          error_1 = error;
          error   = set - vout;
          acc_err = acc_err + error;

          pwm     = pwm + (Kp*error) + (Kd*(error-error_1)/T) + (Ki*acc_err*T);

          if(pwm>=255){
          pwm  = 255;
          }
          else if(pwm<0){
          pwm = 0;
          }

          Pwm_Change_Duty(pwm);

     }
}

 

[dougy83]

If you're using the simulator, set a breakpoint on one of the instructions in the loop then use the stopwatch to time a single loop.

If you're trying it out in hardware, toggle a pin at the start of each loop. The frequency of the pin will be half the loop frequency.

As an aside, using floating point calculations on a PIC16F will be quite slow; you may wish to consider using fixed-point (i.e. integer math)