Electronic – Can’t trigger AVR ADC Interrupt

avrinterrupts

I am using an Atmel's XPlained mini board with Atmega328PB. I am trying to use ADC interrupt, however I can't get it to fire. Here's the code that I have a problem with:

#define F_CPU 16000000UL
#include <avr/io.h>
#include <avr/interrupt.h>


ISR(ADC_vect){
    PORTC ^= (1<<PINC2);
}

int main(void)
{
DDRC |= (1<<PINC2); //pin 2 as output
DDRC &= ~(1<<PINC3); //adc pin as input
sei();
ADMUX |= (1<<REFS0); //reference voltage VCC
ADMUX |= (1<<MUX0);
ADMUX |= (1<<MUX1);// channel 3
ADCSRA |= (1<<ADPS2);//
ADCSRA |= (1<<ADPS1);//
ADCSRA |= (1<<ADPS0);//prescaler to 128
ADCSRA |= (1<<ADATE);//auto trigger enable
ADCSRA |= (1<<ADIE); //adc interrupt enable
ADCSRA |= (1<ADEN); //adc enable
ADCSRA |= (1<< ADSC); //start conversion    

while (1) 
    {
    }
}

As far as I understand the code should enable a constant conversion in a free running mode with the frequency of 16MHz/128, and each time the conversion is completed the ADC_vect should fire toggling PIN2 of Port C. The problem is it doesn't. I am guessing I am not initializing the ADC correctly, however I can not pin point were the problem is.

EDIT:
After pointing out that the adc was not being run in a free running mode I cleared the ADTS bits. However I still couldn't toggle the pin. I think something else is at fault here.

Best Answer

You've written 

ADCSRA |= (1<ADEN); //adc enable

And I think it should be

ADCSRA |= (1<<ADEN); //adc enable

Which seems plausible since the error you've come across is that it never does anything.

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