PX4 User Guide (v1.12)

# I2C Bus Overview

I2C is a packet-switched serial communication protocol that allows multiple master devices to connect to multiple slave devices using only 2 wires per connection. It is intended for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.

Pixhawk/PX4 support it for:

  • Connecting off board components that require greater data rates than provided by a strict serial UART: e.g. rangefinders.
  • Compatibility with peripheral devices that only support I2C.
  • Allowing multiple devices to attach to a single bus (useful for conserving ports). For example, LEDs, Compass, rangefinders etc.

TIP

IMUs (accelerometers/gyroscopes) should not be attached via I2C (typically the SPI (opens new window) bus is used). The bus is not fast enough even with a single device attached to allow vibration filtering (for instance), and the performance degrades further with every additional device on the bus.

# Integrating I2C Devices

Drivers should #include <drivers/device/i2c.h> and then provide an implementation of the abstract base class I2C defined in I2C.hpp for the target hardware (i.e. for NuttX here (opens new window)).

A small number of drivers will also need to include headers for their type of device (drv_*.h) in /src/drivers/ (opens new window) - e.g. drv_airspeed.h (opens new window).

To include a driver in firmware you must add the driver to the board-specific cmake file that corresponds to the target you want to build for. You can do this for a single driver:

drivers/distance_sensor/lightware_laser_i2c

You can also include all drivers of a particular type.

distance_sensor # all available distance sensor drivers

TIP

For example, you can see/search for distance_sensor in the px4_fmu-v4_default (opens new window) configuration.

# I2C Driver Examples

To find I2C driver examples, search for i2c.h in /src/drivers/ (opens new window).

Just a few examples are:

# Further Information

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