Honored Contributor
Honored ContributorCustom instructions are coupled to the ALU so the best you could do is save a couple of them (2-3 actually). Custom instructions are meant for receiving 2-3 inputs and outputting a single result back to the NIOS core. So in short no this would not be possible.
I'm curious, what is the hard deadline that your ISR needs to process? Also what memory are you using for code and ISR code? (you would want your "fast" code to be in fast memory (on chip memory)). So I would look into that, and also if you can operate your NIOS core faster you may want to do that as well (if you are using Stratix you can easily clear 100MHz). Good-luck
