Soft debouncing from an interrupt during stand-by

Question

My current setup has the arduino in 'stand-by' power saving mode, therefore i am unable to use any means of a traditional soft debouncer, such as Bounce2, as far as I know.

I went ahead and attached the buttons to pin change interrupts, since I have one button on each bank, i.e. pin 7 and pin 11.

The technique I'm using doesn't seem to be behaving since the routines are being fired too regularly (inconsistently), and at the rising edge too.

I have the pins set to use their internal pull-ups.

Using the PCI library:

void pciSetup(byte pin)
{
  *digitalPinToPCMSK(pin) |= bit (digitalPinToPCMSKbit(pin));  // enable pin
  PCIFR  |= bit (digitalPinToPCICRbit(pin)); // clear any outstanding interrupt
  PCICR  |= bit (digitalPinToPCICRbit(pin)); // enable interrupt for the 

pciSetup(POWER_SWITCH);
pciSetup(SELECTOR_BTN);

// check if IR IN or Power switch
ISR (PCINT0_vect) // handle pin change interrupt for D8 to D13 here
{

  if (digitalRead(POWER_SWITCH) == LOW)
  {
    noInterrupts();
    unsigned long last_millis = millis();
    while (millis() - last_millis >= 500);
    ir_power_pressed = true;
  }
  interrupts();
}

ISR (PCINT2_vect) // handle pin change interrupt for D0 to D7 
  noInterrupts();
  unsigned long last_millis = millis();
  while (millis() - last_millis >= 500);
  ir_selector_pressed = true;
  interrupts();
}

Am I doing something silly?

Update 1

As suggested in the comments, i've adjusted the code, but it still triggers on the rising edge, and a few times rapidly at the falling edge.

ISR (PCINT2_vect) // handle pin change interrupt for D0 to D7 here
{
  if (digitalRead(SELECTOR_BTN) == LOW)
  {
    noInterrupts();
    static unsigned long last_millis = millis();
    if (millis() - last_millis >= 500)
    {
      ir_selector_pressed = true;
      interrupts();
    }
  }
}

Answer 1

You don't update last_millis.
Also, you don't know whether SELECTOR_BTN went from HIGH to LOW or whether another pin fired the interrupt while SELECTOR_BTN was low. Remember the previous state to solve this.

const unsigned long debounceTime = 50;
volatile bool ir_selector_pressed = false;

ISR (PCINT2_vect) { // handle pin change interrupt for D0 to D7 here
  static unsigned long previousStateChangeMillis = 0;
  static bool previousPinState = HIGH;

  bool pinState = digitalRead(SELECTOR_BTN);
  if (pinState != previousPinState) { // ignore pin changes of pins other than SELECTOR_BTN
    if (pinState == LOW) { // only falling events
      if ((millis() - previousStateChangeMillis) > debounceTime) { // debounce
        ir_selector_pressed = true;
      }
    }
    previousPinState = pinState;
    previousStateChangeMillis = millis();
  }
}