Taking that definition ‘activity’ loosely, what happens if you write to the interrupt pin? Maybe that counts as activity?
I just had a look at the datasheet (13. External Interrupts), and it actually does say …
Observe that, if enabled, the interrupts will trigger even if the INT7:0 or PCINT23:0 pins are configured as outputs. This feature provides a way of generating a software interrupt.
It seems a mode change may even be enough… i.e. changing it from an input to an output…
