I2C Interface

1. I2C Pins

There are two groups of I2C available on the 40PIN pins, namely i2c-5 and i2c-8.

I2C	Pin	Function
I2C5-SCL	27	I2C5 clock signal line
I2C5-SDA	28	I2C5 data line
I2C8-SCL	3	I2C8 clock signal line
I2C8-SDA	5	I2C8 data line

2. I2C Interface Enable

These two interfaces can be enabled by modifying the device tree.

    &i2c5{
        status = "okay";
    };

    &i2c8{
        status = "okay";
    };

3. Mount I2C Device

When registering an I2C device, you need the i2c_client structure to describe the I2C device. However, in standard Linux, users only need to provide corresponding I2C device information, and Linux will construct the i2c_client structure based on the provided information.

The I2C device information provided by users is written as nodes in the DTS file, as follows:

    &i2c5{
        nca9555:nca9555@20{
            reg=<0x20>;
            compatible = "novosense,nca9555";
            status="okay";
            gpio-controller;
            #gpio-cells = <2>;
        };
    };

The driver mounts the device by obtaining node information from DTS.

Note

NCA9555 is a 24-pin CMOS device that provides 16-bit general parallel I2C bus input/output GPIO expansion function.

4. Check I2C Device

Use the following command to check if the i2c bus is enabled.

As shown in the figure:

5. I2C Testing Tools

The board comes with i2c testing commands: i2cdetect, i2cdump, i2cset, and i2cget. They are used to scan devices on the I2C bus, read/write registers of specified devices, etc.

For example, to view the device situation mounted on i2c5, the output is as follows:

    # i2cdetect -y 5
        0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
    00:          -- -- -- -- -- -- -- -- -- -- -- -- --
    10: -- -- -- -- -- 15 -- -- -- -- -- -- -- -- -- --
    20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    50: -- UU -- -- -- -- -- -- -- -- -- -- -- -- -- --
    60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
    70: -- -- -- -- -- -- -- --

Tips

"15" indicates a device with address 15 but the driver is not loaded. UU indicates a device with address 50 and the driver has been loaded successfully.

Other common command usage examples are as follows:

    # Check how many i2c buses the current system has
    i2cdetect -l

    # View devices on i2c-3 interface
    i2cdetect -a 3

    # Read all register values of the specified device.
    i2cdump -f -y 3 0x20

    # Read the value of a specific register of the specified I2C device, e.g., read register 0x01 from device at address 0x68.
    i2cget -f -y 3 0x20 0x01

    # Write a value to a specific register of the specified I2C device, e.g., set register 0x01 of device at address 0x68 to 0x6f.
    i2cset -f -y 3 0x20 0x01 0x6f b

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