Problem with timer1 interrupt code

Projects Programming
1

I am playing with a basic timer 1 program on an Arduino UNO that’s suppose to blink the on-board LED in so that I can understand exactly how to set up timer interrupts. When I run this, the LED never blinks (the ISR is apparently never called) and setup() seems to repeatedly be called (the "Init..." message is continuously sent to the serial monitor). I assume that some error is causing the board to repeatedly be reset.

Can someone take a look at this to see if I’m missing anything? By the way, when I use the Timer1 class it works fine, therefore I assume it’s something I’m doing (or not doing) rather than some hardware issue.

Attached is a copy of the code.

Thanks,

Jack

TimerInterruptTest1.ino (622 Bytes)

2

The line "#if 0" means "Throw away all the lines between here and #endif". No wonder the code doesn't do what you expect!

void setup() 
{
  Serial.begin(115200);
// initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);

  noInterrupts(); // disable all interrupts
#if 0
  TCCR1A = 0;
  TCCR1B = 0;

  OCR1A = 15264;

  TCCR1B |= (1 << WGM12);
  
  TCCR1B |= (1 << CS10);    // 1024 prescaler
  TCCR1B |= (1 << CS12);

  TIMSK1 |= (1 << OCIE1A);   // enable timer compare interrupt
#endif      
  interrupts(); // enable all interrupts

  Serial.println("Init...");
}

void loop() 
{

}

ISR(Timer1_COMPA_vect) // timer compare interrupt service routine
{
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
}
3

I don't know if the OP has changed his code or not, but I see #if 1.

The issue I see with the code is that the syntax for the ISR is wrong

//ISR(Timer1_COMPA_vect)
ISR(TIMER1_COMPA_vect)

void setup() 
{
  Serial.begin(115200);
// initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);

  noInterrupts(); // disable all interrupts
#if 1
  TCCR1A = 0;
  TCCR1B = 0;

  OCR1A = 15264;

  TCCR1B |= (1 << WGM12);
  
  TCCR1B |= (1 << CS10);    // 1024 prescaler
  TCCR1B |= (1 << CS12);

  TIMSK1 |= (1 << OCIE1A);   // enable timer compare interrupt
#endif      
  interrupts(); // enable all interrupts

  Serial.println("Init...");
}

void loop() 
{

}

//ISR(Timer1_COMPA_vect) // timer compare interrupt service routine
ISR(TIMER1_COMPA_vect)
{
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
}
4

Cattledog - Yes that was it - Thank you very much. Good Catch! I looked at the code and looked at the code and looked at it again, and just didn't see it. I'm surprised the compiler didn't complain about that typo.

Re: The #if 0... Yes that was in the example I originally posted (a remnant of my debugging), but I changed it after reviewing my post. However having said that, that code snippet being turned off would not have explained the apparent constant resets I was seeing.

As an aside, how did you guys insert the code in your reply vs as an attachment? That makes a post much more readable.

Thanks again,

Jack