I2C Driver for CPP

This driver is a C++ class for abstracting I2C write and read commands on a Linux operating system.

Class definition

class I2C_Driver

This class uses the ioctl user-space framework provided by Linux for interfacing with an I2C bus. The key includes to enable this system functionality are:

• #include <fcntl.h>

• #include <linux/i2c.h>

• #include <linux/i2c-dev.h>

• #include <sys/ioctl.h>

More information about ioctl can be found here in the I2C device interface documentation of the Linux kernel. If you encounter errors arising from the ioctl function, this blog post discuss interpretting of the errno.

Enumerations

enum class I2C_Driver::I2C_State : int

A scoped enum for this class that indicates that current state of the I2C connection as either open or closed.

Member variables

private char I2C_Driver::m_device_name[20]

The name of the I2C device that this class interfaces with. For a Linux operating system, the device names are almost always of the form /dev/i2c-1, where the number at the end of the name indicates the specific I2C bus number.

The maximum length of 20 characters for this variable is arbitrarily chosen to be sufficiently longer than any plausible device name.

private I2C_Driver::I2C_State I2C_Driver::m_state

The current state of the I2C device that this instance manages. As per I2C_State, the state can be either open or closed.

private int I2C_Driver::m_file_descriptor

File descriptor of the I2C connection as returned by the operating system when the I2C connection is open. This variable is set to -1 if the connection is closed.

Class constructor

I2C_Driver::I2C_Driver(const char *device_name)

Class constructor that set the device name variable m_device_name. It is not possible to change the device name after construction of the object, you instead need to create a new object with the different device name.

Getter functions

const char *I2C_Driver::get_device_name()

Returns a pointer to the start of the device name variable m_device_name.

int I2C_Driver::get_state()

Returns the value of the connection state variable m_state as an integer.

int I2C_Driver::get_file_descriptor()

Returns the value of the file descriptor variable m_file_descriptor, which is set to -1 if the connection state is closed.

Member functions

bool I2C_Driver::open_i2c_device()

Attempts to open the I2C device with name m_device_name. Uses the open() function provided by the <fcntl.h> header and specifies the mode as 0_RDWR, i.e., read-write mode.

Returns: bool

Boolean flag indicating the status.

true indicates that a valid file descriptor was provided and hence the I2C device is open.

false indicates that I2C device could not be opened, hence the file descriptor is -1.

bool I2C_Driver::close_i2c_device()

Closes the I2C device that corresponds to the value of the m_file_descriptor variable. Uses the close() function provided by the <fcntl.h> header.

Returns: bool

Boolean flag indicating the status.

true indicates that the device designated by m_file_descriptor was successfully closed, and hence m_file_descriptor was set to -1.

false indicates that there was not an I2C device to close because m_file_descriptor has the value -1.

bool I2C_Driver::write_data(uint8_t address, uint16_t num_write_btyes, uint8_t *write_data_array)

Writes the specified device address on the the I2C bus with the write bit set, and then write the data provided onto the bus, hence sending that data to that device.

Parameters:

uint8_t address

I2C address of the device to communicate with.

uint16_t num_write_btyes

Number of bytes of data to be written.

uint8_t * write_data_array

Pointer to the array that contains the data to be written.

Returns: bool

Boolean flag indicating the status of the I2C write, true for successful, false otherwise.

bool I2C_Driver::write_data_then_read_data(uint8_t address, uint16_t num_write_btyes, uint8_t *write_data_array, uint16_t num_read_btyes, uint8_t *read_data_array)

Writes the specified device address on the the I2C bus with the write bit set, and then write the data provided onto the bus, hence sending that data to that device. Subsequently listens for and reads the number of bytes specified.

Parameters:

uint8_t address

I2C address of the device to communicate with.

uint16_t num_write_btyes

Number of bytes of data to be written.

uint8_t * write_data_array

Pointer to the array that contains the data to be written.

uint16_t num_read_btyes

Number of bytes of data to be read.

uint8_t * read_data_array

Pointer to the array where the read data is stored.

Returns: bool

Boolean flag indicating the status of the I2C write-then-read, true for successful, false otherwise.

bool I2C_Driver::check_for_device_at_address(uint8_t address)

Checks whether or not there is a device connected at the specified address.

There is no standard I2C detection command or function. The method used by this function to write one byte with value 0x00 to the specified address and then attempt to read one byte worth of response.

Important

This detection method works well for most devices. However, is not guaranteed to work for all devices and can in some circumstances it cause unexpected behaviour (see Ubuntu manual page for i2cdetect for further information).

Parameters:

uint8_t address

I2C address to check whether there is a device currently connected.

Returns: bool

Boolean flag indicating the status for that address.

true indicates that a byte of data was receive in response to probing the address, hence that is a device connected at the address.

false indicates that no response was received, hence it is unlikley for there to be a device connected at the address.