ATmega32 analog comparator code with interrupts not working

Question

I wrote a code for my ATmega32 to light an LED using the analog comparator's interrupts but the ISR won't execute. I'm testing on Proteus.

#define F_CPU 8000000UL

#include <avr/io.h>
#include <avr/interrupt.h>

#define LED_DDR     DDRA                ///< DDR of indicator LED.
#define LED_PORT    PORTA               ///< Port of indicator LED.
#define LED_PIN     PA0                 ///< Pin of indicator LED.

void PORT_INIT(void);
void COMPARATOR_INIT(void);

/*!
 *  @brief ISR for Analog Comparator Interrupt; turn on LED if an interrupt occurs.
 */

ISR(ANA_COMP_vect){
    LED_PORT |= (1<<LED_PIN);
}

int main(void){
    PORT_INIT();
    COMPARATOR_INIT();
    
    sei();                              ///< Enable global interrupts.
    
    while(1);
}

/*!
 *  @brief Initialize ports.
 */

void PORT_INIT(void){
    LED_DDR |= (1<<LED_PIN);
}

/*!
 *  @brief Initialize Analog Comparator.
 */

void COMPARATOR_INIT(void){
    ACSR = 0x00;                    ///< Enable Analog Comparator by setting ACD to 0.
    ACSR |= (ACIE)|(ACIS1);         ///< Enable Analog Comparator Interrupt and set Interrupt Mode to Falling Output Edge.
}

I added a line of code to toggle another pin between the while loop to see if any interrupts at all occur but the pin inside the while loop keeps toggling. Am I missing something here?

Answer 1

Edit:

The ATMega32 bit macros are the actual bit numbers (0, 1) and need to be leftshifted when used in bitwise expressions with the registers.

ACSR |= (ACIE)|(ACIS1);
should be
ACSR |= (1 << ACIE)|(1 << ACIS1);

---

There's lots of things that could go wrong here. and I don't see anything obviously wrong (other than the above).

I added a line of code to toggle another pin between the while loop to see if any interrupts at all occur but the pin inside the while loop keeps toggling

I don't understand what this means - could you add a code snippet for this test?

Here's a couple of troubleshooting steps I'd take.

1. Can you verify that this code can light up the LED?

This could isolate a problem with the LED code / circuit.
Try some main function like this:

#include <util/delay.h>
//...
int main(void){
    PORT_INIT();
    //COMPARATOR_INIT();
        
    //sei();                              ///< Enable global interrupts.
        
    while(1)
    {
        LED_PORT |= (1<<LED_PIN);
        _delay_ms(1000);
        LED_PORT = 0;
        _delay_ms(1000);
    }
}

}

2. If that works, there's more to check on with the Comparator.

How are you stimulating the comparator input? Do you have a voltmeter to verify the comparator should be triggered? What pins are you applying the voltage to?