I got a kernel level ISR working for a data acquisition project. I found that user level ISRs (with wiringPi for example) have a latency of 25us and up. I needed a little better so I came up with this kernel level driver for interrupting on the rising edge of a gpio and writing data to a file, latency is reduced to 2.5us to 7us. There were lots of challenges, I put a description of the project here https://sites.google.com/site/hamlinhom ... rry-pi-isr
the source code is attached.