Nunchuk Driver

A sample Linux I2C driver for the Nintendo Wii Nunchuk (RVL-004). The driver supports the following inputs using the input subsystem:

• Z Button
• C Button
• Joystick (X and Y)

This project is based on Bootlin's embedded Linux trainings (see References section below).

Tested on BeagleBone Black hardware running mainline Linux version 5.10.179.

Hardware

• BeagleBone Black
• Nintendo Wii Nunchuk
• UEXT connector for Wii Nunchuck

Building the kernel module

To cross-compile, run the following command (using a cross-compiling toolchain provided by Ubuntu as an example):

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-

Device Tree

To enable Nunchuk functionality on your board, add the following entry to the device tree:

&i2c1 {
	pinctrl-names = "default";
	pinctrl-0 = <&i2c1_pins>;
	
	status = "okay";
	clock-frequency = <100000>;
	
	joystick@52 {
		compatible = "nintendo,nunchuk";
		reg = <0x52>;
	};
};

Nunchuk

Connect the Nunchuk to the I2C1 bus of the BeagleBone Black board (pins 17 and 18 of P9, see pinout). The Nunchuk should show up at address 0x52:

# i2cdetect -r 1
i2cdetect: WARNING! This program can confuse your I2C bus
Continue? [y/N] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- 52 -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Load the kernel module to verify the driver finds the device:

# modprobe nunchuk

Finally, run the evtest application to test the inputs:

# evtest

References

• Bootlin: Embedded Linux kernel and driver development training.