frequency meter using Adafruit Feather M0
The Feather is Arduino Zero compatible (at least it uses the same processor) and can use the Arduino IDE for development and compiler. The code you have for FreqMeasure is written for Arduino so it should be basically the same 'C' code for the new variant of Arduino.
You may have to tweak pin numbers and if there is any inline assembler, convert that to ARM code, but the bulk of the 'C' code should be identical.

You might start reading here: https://www.arduino.cc/en/Guide/ArduinoZero