How to: I²C Bus

This article will demonstrate how to interface I²C target devices (CHESTER is I²C controller on the bus).

caution

From the Zephyr perspective, the correct way to interface I²C target devices, is to create a proper device driver following the Zephyr device driver model.

However, for simple proof-of-concept purposes, the following guide can be used.

Code Example

Enable the I²C bus in the file prj.conf:

CONFIG_I2C=y

Include the required files in your implementation file:

#include <zephyr/device.h>
#include <zephyr/devicetree.h>
#include <zephyr/drivers/i2c.h>
#include <stderr.h>
#include <stdint.h>

This is an example function to read a single data byte from a specific register:

static int read(uint8_t devaddr, uint8_t regaddr, uint8_t *regval)
{
    int ret;

    const struct device *dev = DEVICE_DT_GET(DT_NODELABEL(i2c0));

    if (!device_is_ready(dev)) {
        LOG_ERR("Device not ready");
        return -ENODEV;
    }

    ret = i2c_write_read(dev, devaddr, &regaddr, 1, regval, 1);
    if (ret) {
        LOG_ERR("Call `i2c_write_read` failed: %d", ret);
        return ret;
    }

    return 0;
}

This is an example function to write a single data byte from a specific register:

static int write(uint8_t devaddr, uint8_t regaddr, uint8_t regval)
{
    int ret;

    const struct device *dev = DEVICE_DT_GET(DT_NODELABEL(i2c0));

    if (!device_is_ready(dev)) {
        LOG_ERR("Device not ready");
        return -ENODEV;
    }

    uint8_t buf[2] = { regaddr, regval };

    ret = i2c_write(dev, buf, 2, devaddr);
    if (ret) {
        LOG_ERR("Call `i2c_write` failed: %d", ret);
        return ret;
    }

    return 0;
}

I²C Scan

You can use a shell command i2c scan i2c@40003000 to do an I²C bus scan.

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:             -- -- -- -- -- -- -- -- -- -- -- --
10: 10 -- -- -- -- -- -- -- -- 19 -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- 48 -- -- 4b -- -- -- --
50: -- 51 -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
6 devices found on i2c@40003000

The addresses of I2C sensors are in the I²C Address Space article.

References

If you need more details on the Zephyr I²C API, see the Zephyr API documentation: https://docs.zephyrproject.org/latest/hardware/peripherals/i2c.html