Do ISRs have to be defined in top level Arduino program?

Question

I'm currently attempting to implement some interrupts on an Arduino project. Looking through some of the examples, it appears that all the ISRs are defined in the top level Arduino program. I'm organizing my project by C++ classes and namespaces, so I'm curious, is it possible to reference an ISR that is not declared and defined in the top level Arduino program? Could I instead reference an ISR that is declared in a separate C++ namespace? This question has been spawned primarily for organizational purposes.

Otherwise, I could always just use a #include to import a file that defines the ISR such that they're imported to the top level.

Thanks!

• Edgar Bonet: Are you talking about a real ISR, or a function that you use with attachInterrupt()?
• Izzo: @EdgarBonet A function that I use with attachInterrupt().
• Edgar Bonet: Then it should be declared (not necessarily defined) from where you use it, or in an included .h.

Answer 1

Why don't you try it and see?

is it possible to reference an ISR that is not declared and defined in the top level Arduino program? Could I instead reference an ISR that is declared in a separate C++ namespace?

Yes. Example here:

const byte LED = 13;
const byte BUTTON = 2;
namespace foo
 {
 // Interrupt Service Routine (ISR)
 void switchPressed ()
 {
 if (digitalRead (BUTTON) == HIGH)
 digitalWrite (LED, HIGH);
 else
 digitalWrite (LED, LOW);
 } // end of switchPressed
 } // end of namespace foo
void setup ()
{
 pinMode (LED, OUTPUT); // so we can update the LED
 digitalWrite (BUTTON, HIGH); // internal pull-up resistor
 attachInterrupt (0, foo::switchPressed, CHANGE); // attach interrupt handler
} // end of setup
void loop ()
{
 // loop doing nothing 
} 

I put the ISR in the namespace "foo" and it compiled OK.