void setup() 
{
  Serial.begin(9600);
  Serial.println("Interrupt timer2 calculator");
  Serial.println("--------------------");
}

void loop() 
{

while (Serial.available() == 0) {}
  
  int value = Serial.parseInt();
  float Freq;
  int Puls10Mtr=6522;
  float CompareReg;

  if(value > 0)
  {
    Freq=value/3600.0*(Puls10Mtr/10);
    Serial.print("Fequency: ");
    Serial.print(Freq,5);
    Serial.println(" Hz");
    CompareReg=(16000000/(1*Freq))-1;
    if (CompareReg<65536){
      Serial.println("CS12 - CS10 = 001 : divide by 1");
      goto Found;
    }
    CompareReg=(16000000/(8*Freq))-1;
    if (CompareReg<65536){
      Serial.println("CS12 - CS10 = 010 : divide by 8");
      goto Found;
    }
    CompareReg=(16000000/(64*Freq))-1;
    if (CompareReg<65536){
      Serial.println("CS12 - CS10 = 011 : divide by 64");
      goto Found;
    }
    CompareReg=(16000000/(256*Freq))-1;
    if (CompareReg<65536){
      Serial.println("CS12 - CS10 = 100 : divide by 256");
      goto Found;
    }
    CompareReg=(16000000/(1024*Freq))-1;
    if (CompareReg<65536){
      Serial.println("CS12 - CS10 = 101 : divide by 1024");
      goto Found;
    }  
    Found:
    Serial.print("compare match register: ");
    Serial.println(CompareReg);
    OCR2A=word(CompareReg);

    TCCR1A = 0;// set entire TCCR1A register to 0
    TCCR1B = 0;// same for TCCR1B
    TCNT1  = 0;//initialize counter value to 0
    // set compare match register
    OCR2A=word(CompareReg);//(must be <65536)
    // turn on CTC mode
    TCCR1B |= (1 << WGM12);
    // Set CS12 and CS10 bits for 1024 prescaler
    TCCR1B |= (1 << CS12) | (1 << CS10);  
    // enable timer compare interrupt
    TIMSK1 |= (1 << OCIE1A);

 
  }   
}