Timer2 off by a factor of 2

Projects Programming
1

I have the following code running on an Arduino Nano:

volatile int x = 1000;
bool y = 0;
volatile long a = 0;
long b = 0;


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  TCCR2A |= 0;
  TCCR2B |= 0x04; //prescaler set to 1/64
  OCR2A |= 0xFF;  //this can be adjusted later
  TIMSK2 |= 0b10;  //set interrupts
  Serial.println(TCCR2B,BIN);
  
  

}

void loop() {
  // put your main code here, to run repeatedly:

 if(y == 1){
  Serial.println(a-b);
  b = micros();
  y=0;
 }
}

SIGNAL(TIMER2_COMPA_vect){
  if(x==0){
    a = micros();
    y = 1;
    x = 1000;
  }

  x--;
}

I would expect that with a 16mhz system clock and a divider of 64 that the interrupt should trigger roughly once every millisecond and decrementing a counter down from 1000 should give me an output every second. What I'm getting though is over 2 seconds.

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Thoughts?

2

Okay I figured it out. I guess the tone() function fiddles with those registers and OR'ing them with a bit mask was leaving some of their bit values. I changed:

  TCCR2A |= 0;
  TCCR2B |= 0x04; //prescaler set to 1/64
  OCR2A |= 0xFF;  //this can be adjusted later

to:

  TCCR2A = 0;
  TCCR2B = 0x04; //prescaler set to 1/64
  OCR2A = 0xFF;  //this can be adjusted later