Introduction U3 I/O shield on ubuntu

The ODROID-U3 I/O Shield board can be plugged on the neat of ODROID-U3 via tiny 8 pin and 4 pin IO connector.
The shape and dimension are exactly same as ODROID-U3. It comes with 12pcs of PCB spacers for easier and solid stacking assembly.
The IO shield has 3 blocks.

• I2C IO expansion block
• Arduino Compatible block
• SPI Interface block(ODROID-U3+ and I/O shield Rev_0.3 or later)

TI's TCA6416A I2C to Parallel Port Expander is used in this block.
The major benefit of this device is its wide VCC range.
It can operate from 1.65 V to 5.5 V on the P-port side and on the SDA/SCL side separately.
It allows bidirectional voltage-level translation GPIO Expansion between 1.8V SCL/SDA(VCCI) and 5Volt Port(VCCP).

Standard Linux kernel have inside a special interface allow to access to GPIO pins.

1. Need to super-user permition

sudo su
[sudo] password for odroid : odroid

2. Load the kernel modules

modprobe i2c-gpio-custom bus0=4,200,199
modprobe gpio-pca953x

3. Set the I2C address of the module

echo tca6416 0x20 > /sys/devices/platform/i2c-gpio.4/i2c-4/new_device 

4. Enable GPIO's on the board.
If Kernel version is higher than 3.8.13.30 gpio_n = 341 ~ 356
else Kernel version is older than 3.8.13.30 gpio_n = 289 ~ 304

echo NUM > /sys/class/gpio/export
cd  /sys/class/gpio/gpioNUM
echo out > direction
echo 1 > value
echo 0 > value

Atmel’s ATmega328P is used as a slave CPU to expand the IO port.
You can use the Arduino IDE on ODROID-U3 to build & upload your sketches to this Arduino-compatible block,
without additional/external cable connections.
Like the Arduino Uno, it has 14 digital input/output pins (of which 6 can be used as PWM outputs),
6 analog inputs which provides 10 bits of resolution. They operate at 5 volts range.