Determining when the motor has stopped with a tachometer

Hello people.

So what's happening is that I've got a tachometer on a grinding wheel. I have it set to interrupt whenever a shiny patch goes by, and then the time between interrupts is measured. The problem that happens is that once it's stopped, I don't get an interrupt and can't determine the time that led to it.

Is it possible to set it up so that if I don't get an interrupt within 100 ms of the last interrupt, something happens?

Not sure what other information to provide, ask me if you need more.

Edit: found the solution to be trivial. Never mind -_-