millis() function always returns same value

Question

I'm trying to program an Arduino MKR1000 and I am using the millis() function to emulate a traditional timer. The problem is that any call to millis() inside the debounceTimer() function returns the same value. I only added the Serial.print to debug.

I left out a decent bit of the code to simplify your reading of it. It works by waiting for an interrupt on pin 4 which then calls the runTimers() function and that calls the debounceTimer() function and within that the millis() function is called. The debouncetimer() function keeps getting called until the 10 ms has elapsed and then should end the timer. The problem is that the millis() function stops returning a value that goes up.

#define doorIntPin 4
unsigned char sysEnabled = 0;
unsigned long debounceTimerPlace =0;
unsigned char debounceTimerOn =0;

void setup() {
  Serial.begin(9600);
  attachInterrupt(doorIntPin, doorOpens, LOW);
  interrupts();
}

void loop() {

}
void runTimers(){
  Serial.print('r');
  while(alarmTimerOn || debounceTimerOn || enablingTimerOn){
     if(alarmTimerOn)
      alarmTimer();
    if(enablingTimerOn)
      enablingTimer();
    if(debounceTimerOn)
      debounceTimer();
  }
}

void debounceTimer(){
  unsigned long time = millis()- debounceTimerPlace;
  Serial.println(millis() & 0xFFFF, DEC);
  if(sysEnabled && time> 10){
    debounceTimerOn=0;
  }
}
void doorOpens() {
  Serial.print('o');
  if(!debounceTimerOn){
      debounceTimerPlace = millis();
      debounceTimerOn=1;
  }
  runTimers();
}

I suspect that in the background an interrupt is being called than increments the value millis() returns and somehow my external interrupt is disabling that. I don't know why this is happening or how to fix it.

Any ideas?

Answer 1

You never exit the ISR, hence all interrupts are disabled. Do the minimum work possible within an ISR, and have the main loop outside.

Answer 2

To answer your question about millis(), it uses interrupts to function, and so you can't call it within an ISR. According to this: https://www.arduino.cc/en/Reference/AttachInterrupt, you should be able to use delayMicrosconds() within an ISR, since it (reportedly) doesn't use interrupts.

Answer 3

The problem is that the millis() function stops returning a value that goes up.

That's right. The value returned by millis() is incremented by an ISR which won't be called inside your other ISR.

You can use micros() which will increment. However that will only be good up to approximately 1 ms. The main rule of ISRs is that you don't attempt to do delays inside them.