Introduction to Embedded Software

Practice #5 Communicate with the Nunchuk over I2C

Dongkun Shin Embedded Software Laboratory

Sungkyunkwan University http://nyx.skku.ac.kr/

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Objective

• Add the WiiNunchuk device to the device tree.

• Write a kernel module for the WiiNunchuk.

- init( ), exit( )

- probe( ), remove( )

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Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Exercise

• WiiNunchuk module

- Register your I2C device driver

- Poll data from the WiiNunchuk every 50ms

- Print the polled data (dmesg)

✓ Joystick X, Y

✓ Accelerometer X, Y, Z

✓ C-button, Z-button

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Review…

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Register WiiNunchuk to the Device Tree

• Override the i2c1 node for the WiiNunchuk

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$ cd linux/arch/arm/boot/dts/ $ vim bcm2710-rpi-3-b.dts

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Rebuild the Device Tree

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$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- zImage modules dtbs -j16

$ scp arch/arm/boot/dts/*.dtb pi@115.145.209.XXX:/home/pi/

$ scp arch/arm/boot/dts/overlays/*.dtb* pi@115.145.209.XXX:/home/pi

$ sudo mv *.dtb /boot/

$ sudo mv *.dtb* /boot/overlays/ $ sudo reboot

Host PC Raspberry Pi

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Check the Device Tree

• Check that the WiiNunchuk device is registered

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$ find /sys/firmware/devicetree/ -name “*nunchuk*”

WiiNunchuk Device Driver

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Exercise

• Complete the WiiNunchuk device driver

- Device initialization

- Input polling

- Device registration

• Due ~ 5/12 (Sun) 23:59:59

- Submit to i-Campus

- File to submit: nunchuk.c

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Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

WiiNunchuk Device Driver• Device initialization

1. Send two bytes to the device (0xf0, 0x55)

2. Send two bytes to the device (0xfb, 0x00)

• Input polling - read device registers

- The nunchuk exhibits a rather weird behavior: it seems that it updates the state of its internal registers only when they have been read.→ WE WILL NEED TO READ THE REGISTERS TWICE

1. Write 0x00 to the bus. This will allow us to read the device registers

2. Read 6 bytes from the device

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Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Functions to Use• i2c_add_driver( ), i2c_del_driver( )

• i2c_transfer( )

• input_event( )

- input_report_key( ), input_report_abs( )

- input_sync( )

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linux/include/linux/i2c.h linux/include/linux/input.h

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

WiiNunchuk Output

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Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Output

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$ sudo modprobe input-polldev $ sudo insmod nunchuk.ko

Introduction to Embedded Software SWE3027-41

Practice #5 2019-05-07

Output

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