Interrupt Counting

What should the interrupt routine do when I press the button? Well, to get this working and feel confident that it *is* working, it's a good idea to make the interrupt routine increment a counter and watch the counter variable in the debugger. That way one button press should be seen equal one counter increment. So my skeletal interrupt routine would be like:

unsigned long volatile counter = 0;

/* External Interrupt Function called when EXINT0 occurs */
void pressed (void) __irq {
counter++;
...
}