[BitTwiddler]

The WPI Library in the Functions Palette contains some vi(s) specific to the Counter functions built-in to the Crio's FPGA. One of the outputs of the Get Counter VI is the period between input pulses. Use that output to calculate the RPM value. See some of the example code for how to use the counter.

The Crio's FPGA takes a lot of the processing load off of the on-board computer so you don't have to try to do it all in software.