The function of wakeUpPin?

[sxontheway]

Hi, I am wondering that in "powerDownWakeExternalInterrupt.ino", what is the function of "wakeUpPin = 2" ? Since the variable wakeUpPin does not be invoked anywhere during the loop(). Does it mean that any voltage changes on any pin can wake up the system?

[percz]

Interrupts interrupt whatever loop() is doing.

You can have a long list of lines in a function, but if your interrupt is triggered the processor will jump to whatever function is linked to it ( in this example wakeUp() )

Arduino actually does this for millis(). No matter what else your own loop code is doing, it will very quickly stop at exactly a certain time, update the millis() value a little then return to where it left your own code.

[sxontheway]

Interrupts interrupt whatever loop() is doing.

You can have a long list of lines in a function, but if your interrupt is triggered the processor will jump to whatever function is linked to it ( in this example wakeUp() )

Arduino actually does this for millis(). No matter what else your own loop code is doing, it will very quickly stop at exactly a certain time, update the millis() value a little then return to where it left your own code.

Thanks for your answer. I searched online and found that the code in line22 of the powerDownWakeExternalInterrupt.ino is usually written as attachInterrupt(digitalPinToInterrupt(interruptPin), wakeUp, LOW);.

I find the definition:
#define digitalPinToInterrupt(p) ((p) == 0 ? 2 : ((p) == 1 ? 3 : ((p) == 2 ? 1 : ((p) == 3 ? 0 : ((p) == 7 ? 4 : NOT_AN_INTERRUPT)))))

Does it means that for Arduino (AVR versions), certain pins have certain interrupt numbers? So if we use attachInterrupt(0, wakeUp, LOW); actually we define pin3 as the interrupt pin?