Analog input interrupt - UNO

[burumdev]

Hi!

Trying to figure out how to read a 10k ohm potentiometer value using an interrupt. My Arduino Uno connections are:
5v VCC -> Pot input
A0 Analog input -> Pot output
GND -> Pot ground

The idea is to use an ADC interrupt handler function to enable a global flag to signal the main loop to read the analog to digital converter value.

ADC function should handle an interrupt when conversion is complete according to docs. Then should I read the value from the register instead of doing an analog_read()?

The code I'm trying for that is:

#![no_std]
#![no_main]
#![feature(abi_avr_interrupt)]

use panic_halt as _;

use core::sync::atomic::{AtomicBool, Ordering};

use arduino_hal::prelude::*;
use arduino_hal::adc;

static READ_POT: AtomicBool = AtomicBool::new(false);

#[avr_device::interrupt(atmega328p)]
#[allow(non_snake_case)]
fn ADC() {
    READ_POT.store(true, Ordering::SeqCst);
}

fn read_pot() -> bool {
    READ_POT.load(Ordering::SeqCst)
}

#[arduino_hal::entry]
fn main() -> ! {
    let dp = arduino_hal::Peripherals::take().unwrap();
    let pins = arduino_hal::pins!(dp);
    
    let mut serial = arduino_hal::default_serial!(dp, pins, 57600);

    dp.ADC.adcsra.write(|w| w.adie().set_bit());

    let mut adc = arduino_hal::Adc::new(dp.ADC, Default::default());

    let (vbg, gnd, temp) = (
        adc.read_blocking(&adc::channel::Vbg),
        adc.read_blocking(&adc::channel::Gnd),
        adc.read_blocking(&adc::channel::Temperature),
    );

    ufmt::uwriteln!(&mut serial, "Vbandgap: {}", vbg).unwrap_infallible();
    ufmt::uwriteln!(&mut serial, "Ground: {}", gnd).unwrap_infallible();
    ufmt::uwriteln!(&mut serial, "Temperature: {}", temp).unwrap_infallible();

    let analog_pin = pins.a0.into_analog_input(&mut adc);

    unsafe {
        avr_device::interrupt::enable();
    }

    loop {
        if read_pot() {
            let value = analog_pin.analog_read(&mut adc);
            ufmt::uwriteln!(&mut serial, "Analog input 0 value: {}", value).unwrap_infallible();
            READ_POT.store(false, Ordering::SeqCst);
        }
    }
}

When I run this code, I can see voltage band gap, ground and temperature values printed. Which means ADC works. But I can't see any a0 value printed and ADC() interrupt handler function seems not getting fired at all.

When I poll the a0 input instead of interrupt I can see the values printed.

What am I missing here? Thanks.