arduino_joystick is an I2C joystick device for RaspberryPi.
It is made of Arduino Uno and Joystick Shield kit(https://www.sparkfun.com/products/9760).
I2C level converter is necessary for connecting Arduino Uno(5V) and RaspberryPi(3.3V).
GPIO pins are used for the input interrupt.
(See schematic.pdf)

firmware/arduino_joystick.ino
Sketch for Arduino

driver/arduino_joystick.c
Device driver for RaspberryPi(Raspbian)

How to use:

1.Compile and upload arduino_joystick.ino

2.Compile driver
First, kernel needs to be buit.
Following command makes arduino_joystick.ko
make -C /usr/src/linux M=$PWD modules

3.Install driver
insmod arduino_joystick.ko

4.Make i2c adapter detect arduino_joystick
echo arduino_joystick 0x20 > /sys/class/i2c-adapter/i2c-1/new_device

5.Test the joystick
Joystick device appears in /dev/input.
Following command tests the joystick.
jstest /dev/input/js0