LUFA
The LUFA library is Dean Camera's excellent USB library that makes it easy to make full use of the ATmega32U4 USB capabilities on the AVRPi-32U4.
The LUFA example directory that is installed through the setup menu contains a slightly modified LUFA version that adds the AVRPi-32U4 board. The examples are taken from the LUFA example directory and 'ported' to the AVRPi-32U4 board. Only the button and LED configuration needed changing for the most part.
cd src/LUFA-AVRPI32U4/examples/Keyboard make avrdude
When you connect a USB cable from the board to a linux computer (such as the Pi), run 'lsusb' and look for an 'Atmel Corp. LUFA *' USB device.
pi@raspberrypi ~ $ lsusb Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. Bus 001 Device 007: ID 03eb:2042 Atmel Corp. LUFA Keyboard Demo Application pi@raspberrypi ~ $
If you press the 'USR' button, the USB keyboard from the demo will generate 'F' characters.
Default configuration (overwrite with 'Board' directory in project):
Joystick.h: PORTF JOY_PRESS: PINF1 JOY_LEFT: PINF4 JOY_UP: PINF5 JOY_DOWN: PINF6 JOY_RIGHT: PINF7 Buttons.h: PORTE BUTTONS_BUTTON1: PINE2 BUTTONS_BUTTON2: PINE6 LEDs.h: PORTB LEDS_LED1: PINB0 LEDS_LED2: PINB1 LEDS_LED3: PINB2 LEDS_LED4: PINB3