Stuck in ISR

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#1
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Total votes: 0

Hello,

I have an ATTiny85 and am trying to generate a tone when INT0 pin goes low. When I connect the PB2 (INT0) pin to ground (low level), the tone starts, but when I pull out the wire, I would expect the tone to go away (end ISR routine), but the tone stays on...don't know why. Any hints shall be appreciated.

Thanks

My code is as follows:

 #define F_CPU 1000000
 #include 
 #include 
 
 #define SPEAKER PB0 
    
 int main (void)
 {   
	 GIMSK |= (1<<INT0);
	 DDRB &= ~(1<<PB2);	 	 
	 DDRB |= (1 << SPEAKER);
	 PORTB |= (1 << PB2);
	 sei();	     
	
	 for(;;)
       {
	}
 return 0;
	 }
	 
	 ISR(INT0_vect)
	 {

TCCR0A |= ((1 << COM0A0)|(1 << WGM01)); // Configure timer 0 for CTC mode and toggle OC0A on compare match
		
OCR0A = 90;// Set CTC compare value
 for (int i=0; i<100; i++)
{
	 for(int j=0; j<255; j++)
	 {
       TCCR0B |= (1 << CS01); //clock/8 prescalar
	 } 
 } 

}
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Total votes: 0

All your ISR does is configure Timer 0 to generate a square wave. In pseudocode, you have...

main(){
  configure_interrupt;
  configure_output;
}

ISR(){
  configure_timer;
  start_square_wave;
}

You never stop the timer, so it continues to generate the tone.
What would work is more like...

main(){
  configure_interrupt;
  configure_output;
  configure_timer; // but do not start it!
}

ISR(){
  start_timer;

  do{
    nothing
  } while_interrupt_is_low;

  stop_timer;
}
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Total votes: 0

A blocking ISR is a completely wrong approach - it does exactly the same that the main loop would do, but complicates the code and brings additional headaches on contact bounce. What you should do is implementing a contact debounce, detect your contact's DEBOUNCED raising and falling edges and then just start a tone upon one edge detect and stop it upon another edge detect.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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Total votes: 0

Thanks guys!