DirectIO

DirectIO is a fast, simple I/O library for AVR, SAM, and SAMD boards. It provides a simple API for doing digital I/O 40-60x faster than the Arduino standard libraries. You can read or write a digital pin in a sinle clock cycle on an AVR-based board. Accelerated support is available for AVR, SAM, and SAMD boards. Other boards are supported in a fallback mode without acceleration.