I2C

I2C API.

Functions for the Inter-IC-Communication Bus

Sysprops

sysprop	description
gpio_sda	SDA GPIO
gpio_scl	SCL GPIO

Example

#include <i2c.h>

#define SENSOR_ADDR    0x68
#define REG_WHO_AM_I   0x75

int sensor_probe(void) {
    int h = open("i2c0");
    if (h < 0) return -1;

    uint8_t id = 0;
    // write-then-read with repeated-start: select register, then read its value
    if (i2c_read_reg(h, SENSOR_ADDR, REG_WHO_AM_I, &id, 1) != 0) {
        close(h);
        return -1;
    }

    close(h);
    return id;
}

Functions Overview

	Name
cw_driver_return_t	i2c_read(int hDev, uint8_t addr, uint8_t * data, uint8_t len)
cw_driver_return_t	i2c_read_reg(int hDev, uint8_t addr, uint8_t reg, uint8_t * data, uint8_t len)
cw_driver_return_t	i2c_write(int hDev, uint8_t addr, const uint8_t * data, uint8_t len) Writes a buffer of bytes to an I²C device.
cw_driver_return_t	i2c_write_reg(int hDev, uint8_t addr, uint8_t reg, const uint8_t * data, uint8_t len)
cw_driver_return_t	i2c_transfer(int hDev, uint8_t addr, const uint8_t * data_w, uint8_t len_w, uint8_t * data_r, uint8_t len_r) Performs a combined write-then-read transaction with a repeated start.
cw_driver_return_t	i2c_clear(int hDev) resets a stuck bus by sending 9 clock pulses

Function Details

function i2c_read

cw_driver_return_t i2c_read(
    int hDev,
    uint8_t addr,
    uint8_t * data,
    uint8_t len
)

Parameters:

• hDev device handle as returned by open(const char*)
• addr the 7bit address of the device to read from.
• data buffer holding the space for the data to be read.
• len length of the data buffer in bytes.

Return: 0 if the data has successfully been read.

function i2c_read_reg

cw_driver_return_t i2c_read_reg(
    int hDev,
    uint8_t addr,
    uint8_t reg,
    uint8_t * data,
    uint8_t len
)

Parameters:

• hDev device handle as returned by open(const char*)
• addr the 7bit address of the device to read from.
• reg the device register to read data from
• data buffer holding the space for the data to be read.
• len length of the data buffer in bytes.

Return: 0 if the data has successfully been read.

function i2c_write

cw_driver_return_t i2c_write(
    int hDev,
    uint8_t addr,
    const uint8_t * data,
    uint8_t len
)

Writes a buffer of bytes to an I²C device.

Parameters:

• hDev device handle as returned by open(const char*)
• addr the 7bit address of the device to write to.
• data buffer containing the data to be written.
• len length of the data buffer in bytes.

Return: 0 if the data has been successfully written, negative on error.

function i2c_write_reg

cw_driver_return_t i2c_write_reg(
    int hDev,
    uint8_t addr,
    uint8_t reg,
    const uint8_t * data,
    uint8_t len
)

Parameters:

• hDev device handle as returned by open(const char*)
• addr the 7bit address of the device to write to.
• reg the device register to be written to
• data buffer containing the data to be written.
• len length of the data buffer in bytes.

Return: 0 if the data has been successfully written.

function i2c_transfer

cw_driver_return_t i2c_transfer(
    int hDev,
    uint8_t addr,
    const uint8_t * data_w,
    uint8_t len_w,
    uint8_t * data_r,
    uint8_t len_r
)

Performs a combined write-then-read transaction with a repeated start.

Parameters:

• hDev device handle as returned by open(const char*)
• addr the 7bit address of the device to address.
• data_w buffer containing the bytes to be written.
• len_w length of the write buffer in bytes.
• data_r buffer that receives the bytes read back.
• len_r length of the read buffer in bytes.

Return: 0 if the transaction has been successfully completed, negative on error.

Writes len_w bytes from data_w to the device at addr, issues a repeated-start condition (no STOP in between), and then reads len_r bytes into data_r. This is the typical pattern for register-based devices where the read must immediately follow the register address selection without releasing the bus.

function i2c_clear

cw_driver_return_t i2c_clear(
    int hDev
)

resets a stuck bus by sending 9 clock pulses

Parameters:

• hDev device handle as returned by open(const char*)