so far nobody has requested the use of external interrupts. Although the IPMC does of course use interrupts internally, I’m afraid there are no interrupt capable pins available on the mezzanine connector of the IPMC.
I would check the input signal one per main loop, there is a callback function for that. You will of course not get a quick response time then. May I ask what signal you are monitoring and why you need a “fast” response time (BTW, how fast is fast enough?)