The firmware has been compiled for the following CPUs, listed roughly in order of preference:
| CPU | Known breakout board(s) |
|---|---|
| ATmega32U4 | Teensy 2.0, Adafruit Atmega32u4 Breakout Board |
| AT90USB1286 | Teensy++ 2.0 |
| AT90USB646 v1.0+ | Teensy++ (no longer available) |
| ATmega16U4 v1.0+ | ??? |
Make sure you pick the right .hex file for your dev board!
ATmega32U4 breakout boards are usually the best choice, on a price basis.
AT90USB1286 boards work equally as well, and have more memory (which can be essential if you want to set up a very large number of layers and/or macros), but cost more.
Note: the ATmega16U4 build is very close to 16KB in size, and probably does not leave room for a USB bootloader on the chip.
So, ATmega16U4 based breakout boards are not recommended for novices!
The Teensy family have the PJRC bootloader installed and are programmed using PJRC's Teensy Loader, available for all common OS.
Other breakout boards usually have the Atmel DFU bootloader installed and can be programmed using FLIP.
FLIP is available for Windows and Linux. For Mac OS-X, see this guide on how use DFU-programmer.
Arduino Leonardo can be programmed using avrdude, or the Arduino IDE.