I looked at that, but I don't need EXTERNAL interrupts, I need INTERNAL interrupts. I suppose I could go into the libraries and modify them, but I would think that others have the same problems I do. I have to monitor the RPM of 9 fan tachometers at once. Currently, (in a PIC), I have a 200uSec timer interrupt that scans the tachometer input pins, XORs them with the last reading and increments 9 different counters - 1 for each bit position changed. After a half-second, I read the counters, multiply them by a constant and come up with the fan RPMs - and start all over again. I have to do that simultaneously with running 10 channels of A/D and receiving, processing and responding to SNMP packets coming in at 115Kbaud from a Lantronix MatchPortAR, AND responding to telnet packets coming in at 115Kbaud from the MatchPort's second serial port.
I do that presently with a PIC18F8723 running at 40Mhz. I am considering moving to ATMEL parts, but I want to make certain that the hardware and software tools are easy to learn and use before I spend a lot of time.
So far, I have found lots of neat examples for Arduinos, but easy, fast interrupts are a must, and I can't see many examples using them. I'll keep looking for awhile before I give up.