Waking up an Arduino with Input from a Sensor

Using Arduino Programming Questions
#1

Hello,
I want to use the same IRQ Arduino PIN to wake controller, and to trigger retrieval of the data from a sensor. The first interrupt wakes ATMEGA328. When awake, ATMEGA gets other interrupts to read data from a sensor. If the sensor does not send data for a long time, ATMEGA goes to sleep.

The code below works fine, but I am wondering, does it matter where I put the code line “enableInterrupt(wakePin, wakeUpNow, RISING)”? At setup or under sleepNow(), or in both? I have tested all of them, they all works fine, but I would want to understand, which one works best?

#include <avr/sleep.h>  
#include "EnableInterrupt.h"
#define wakePin 9                // pin used for waking up  
int led=13; 
int count; 

volatile int irq = 0;
void wakeUpNow() {  

  irq=1;
  
}  
 

void setup() {  
    
  enableInterrupt(wakePin, wakeUpNow, RISING); 
  Serial.begin(9600);
}  
  
void sleepNow() {  
  
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);    
    sleep_enable();          
   enableInterrupt(wakePin,wakeUpNow,RISING); 
    sleep_mode();             
  
    sleep_disable();          
   disableInterrupt(wakePin);     
    Serial.println("woke up!"); 
}  
  
void loop() {  
  delay (1000);
  digitalWrite(led, HIGH);  
  delay(1000);  
  digitalWrite(led, LOW); 
  if (irq) 
  {

  irq=0;
  count=0;
  Serial.println( "We have an interrupt!");
   
  //Read data from the sensor
  }
  NeedSleep();
   
}  

 void NeedSleep() 
 {
   count++;  
   Serial.print(count);
   if (count >= 6){ 
      Serial.println("Timer: Entering Sleep mode");
      delay(100);     
      sleepNow();    
      count = 0;     
 
  
 }
 }
#2

I have tested all of them, they all works fine, but I would want to understand, which one works best?

You could look at the source code. What the function does is register a handler for when a particular event happens. You only NEED to do that once. You can do it more than once, but it's like turning on a light that is already on. Useless, that is.

#3