Arduino - Using interrupts freezes processing and serial output?

Question

So, the interrupts seem to work insofar as "interrupting" when an event happens. My only problem is that I the interrupts will occur 2-3 times and everything essentially stops (Serial out, everything).

I was programming the board to output serially a calculated distance based on the output of the HC-SR04 distance IC. The distances are calculated accurately but, like I said earlier, everything seems to freeze. Below is both the code and an image of the serial monitor.

#define TRIGPIN 4
#define ECHOPIN 3
#define RED 2
#define GREEN 13
#define INTNUM 1 //interrupt pin 1 is digital pin 3 on the duemilanove
#define PULSE 10 //microseconds 
#define CYCLETIME 50 //milliseconds

void ledWrite(int), trigPulse(), getTime();
int millisNow, millisPrev = 0;
int microsPrev;

boolean isHigh = false;


void setup() {
  Serial.begin (9600);

  pinMode(TRIGPIN, OUTPUT);
  pinMode(ECHOPIN, INPUT);
  pinMode(RED, OUTPUT);
  pinMode(GREEN, OUTPUT);

  attachInterrupt(INTNUM, getTime, CHANGE);
}

void loop() {
  trigPulse();
  // some other code while waiting on HC-SR04 to interrupt us when echo goes HIGH
}

void trigPulse(){
  if( (millisNow = millis()) - millisPrev >= CYCLETIME){ //sufficient cycle time 
    digitalWrite(TRIGPIN, HIGH);
    delayMicroseconds(PULSE);
    digitalWrite(TRIGPIN, LOW);
    millisPrev = millisNow; //reset clock 
  }
  return;  
}


void ledWrite(int dTime){
  int distance =  dTime/58.2;

  if (distance < 4) {  
    digitalWrite(RED,HIGH); 
    digitalWrite(GREEN,LOW);
  }
  else {
    digitalWrite(RED,LOW);
    digitalWrite(GREEN,HIGH);
  }

  if (distance >= 200 || distance <= 0){
    Serial.println("Out of range");
  }
  else {
    Serial.print(distance);
    Serial.println(" cm");
  }

}

void getTime(){
  int timeNow = micros(); 
  Serial.println("Interrupted");

  if(isHigh == false){
    microsPrev = timeNow; //get time now, pin LOW->HIGH
    isHigh = true;
    Serial.println("Returning ..");
    return;
      }

  else { //pin HIGH->lOW
    ledWrite(timeNow - microsPrev);
    isHigh = false;
    microsPrev = micros();
    Serial.println("Returning ..");
    return;
  } 

  return;
}

Answer 1

I know this is an old thread, but I just came by it having my own problems. The problem here is that you cannot use:

Serial.Print()

Within an interrupt service routine. The reason that the Serial.Print() doesn't work within an ISR is that it uses interrupts to pull the characters out of the serial buffer, but interrupts of a certain level are masked within the ISR. What basically happens is that the arduino throws out all other interrupts that are of a lower priority, which Serial.Read() falls into.

It is documented in a number of places: link1, link2, link3