Simple HalfKay loader / rebooter.


hktool was created as a basic replacement for teensy-loader-cli. teensy-loader-cli was a fundamentally messy and confusing implementation of the HalfKay protocol used by the boot loader chips / code used in Teensy devices.

This reimplementation is a libusb only rewrite of the old loader with a much simplified command line interface and a design which aims for easy end user extensibility to support future Teensy devices. This means that if PJRC release a new teensy device based on a new chip, it should be possible (unless the HalfKay protocol changes considerably) to simply add a new definition for the device in the form of a simple plain text file.


  • (make) GNU Make (or compatible)
  • libusb 1.0 (or compatible)
  • POSIX.1-2001 or later (getopt, nanosleep, glob)

Compilation and Installation

Notes on Implementation