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@@ -4,9 +4,10 @@ I2C is a packet-switched serial communication protocol that allows multiple mast
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It is intended for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.
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Pixhawk/PX4 support it for:
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* Connecting off board components that require higher data rates than provided by a strict serial UART, such as rangefinders.
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* Compatibility with peripheral devices that only support I2C.
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* Allowing multiple devices to attach to a single bus (useful for conserving ports).
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- Connecting off board components that require higher data rates than provided by a strict serial UART, such as rangefinders.
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- Compatibility with peripheral devices that only support I2C.
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- Allowing multiple devices to attach to a single bus (useful for conserving ports).
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For example, LEDs, Compass, rangefinders etc.
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::: info
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@@ -22,15 +23,17 @@ The bus is not fast enough even with a single device attached to allow vibration
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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](https://github.com/PX4/PX4-Autopilot/blob/main/src/lib/drivers/device/nuttx/I2C.hpp)).
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A small number of drivers will also need to include headers for their type of device (**drv_*.h**) in [/src/drivers/](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers) - e.g. [drv_led.h](https://github.com/PX4/PX4-Autopilot/blob/main/src/drivers/drv_led.h).
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A small number of drivers will also need to include headers for their type of device (**drv\_\*.h**) in [/src/drivers/](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers) - e.g. [drv_led.h](https://github.com/PX4/PX4-Autopilot/blob/main/src/drivers/drv_led.h).
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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.
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You can do this for a single driver:
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```
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CONFIG_DRIVERS_DISTANCE_SENSOR_LIGHTWARE_LASER_I2C=y
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```
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You can also include all drivers of a particular type.
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```
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CONFIG_COMMON_DISTANCE_SENSOR=y
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```
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@@ -44,12 +47,13 @@ For example, you can see/search for `CONFIG_DRIVERS_DISTANCE_SENSOR_LIGHTWARE_LA
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To find I2C driver examples, search for **i2c.h** in [/src/drivers/](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers).
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Just a few examples are:
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* [drivers/distance_sensor/lightware_laser_i2c](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/distance_sensor/lightware_laser_i2c) - I2C driver for [Lightware SF1XX LIDAR](../sensor/sfxx_lidar.md).
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* [drivers/distance_sensor/lightware_laser_serial](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/distance_sensor/lightware_laser_serial) - Serial driver for [Lightware SF1XX LIDAR](../sensor/sfxx_lidar.md).
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* [drivers/ms5611](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/barometer/ms5611) - I2C Driver for the MS5611 and MS6507 barometric pressure sensor connected via I2C (or SPI).
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- [drivers/distance_sensor/lightware_laser_i2c](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/distance_sensor/lightware_laser_i2c) - I2C driver for [Lightware SF1XX LIDAR](../sensor/sfxx_lidar.md).
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- [drivers/distance_sensor/lightware_laser_serial](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/distance_sensor/lightware_laser_serial) - Serial driver for [Lightware SF1XX LIDAR](../sensor/sfxx_lidar.md).
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- [drivers/ms5611](https://github.com/PX4/PX4-Autopilot/tree/main/src/drivers/barometer/ms5611) - I2C Driver for the MS5611 and MS6507 barometric pressure sensor connected via I2C (or SPI).
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## Further Information
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* [I2C](https://en.wikipedia.org/wiki/I%C2%B2C) (Wikipedia)
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* [I2C Comparative Overview](https://learn.sparkfun.com/tutorials/i2c) (learn.sparkfun.com)
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* [Driver Framework](../middleware/drivers.md)
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- [I2C](https://en.wikipedia.org/wiki/I%C2%B2C) (Wikipedia)
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- [I2C Comparative Overview](https://learn.sparkfun.com/tutorials/i2c) (learn.sparkfun.com)
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- [Driver Framework](../middleware/drivers.md)
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@@ -4,9 +4,9 @@
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It is recommended for:
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* Connecting offboard components that require low bandwidth and low latency communication, e.g. [rangefinders](../sensor/rangefinders.md), [magnetometers](../gps_compass/magnetometer.md), [airspeed sensors](../sensor/airspeed.md) and [tachometers](../sensor/tachometers.md).
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* Compatibility with peripheral devices that only support I2C.
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* Allowing multiple devices to attach to a single bus, which is useful for conserving ports.
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- Connecting offboard components that require low bandwidth and low latency communication, e.g. [rangefinders](../sensor/rangefinders.md), [magnetometers](../gps_compass/magnetometer.md), [airspeed sensors](../sensor/airspeed.md) and [tachometers](../sensor/tachometers.md).
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- Compatibility with peripheral devices that only support I2C.
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- Allowing multiple devices to attach to a single bus, which is useful for conserving ports.
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I2C allows multiple master devices to connect to multiple slave devices using only 2 wires per connection (SDA, SCL).
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in theory, a bus can support 128 devices, each accessed via its unique address.
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@@ -15,7 +15,6 @@ in theory, a bus can support 128 devices, each accessed via its unique address.
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UAVCAN would normally be preferred where higher data rates are required, and on larger vehicles where sensors are mounted further from the flight controller.
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:::
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## Wiring
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I2C uses a pair of wires: SDA (serial data) and SCL (serial clock).
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@@ -29,7 +28,6 @@ To ensure reliable communication and to reduce crosstalk it is advised to apply
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## Checking the Bus and Device Status
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A useful tool for bus analysis is [i2cdetect](../modules/modules_command.md#i2cdetect).
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@@ -41,8 +39,8 @@ The tool can be run in the PX4 terminal with the following command:
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```
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i2cdetect -b 1
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```
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where the bus number is specified after `-b` parameter
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where the bus number is specified after `-b` parameter
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## Common problems
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@@ -62,8 +60,9 @@ The bandwidth available for each device generally decreases as more devices are
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If too many devices are added, it can cause transmission errors and network unreliability.
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There are several ways to reduce the problem:
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* Dividing the devices into groups, each with approximately the same number of devices, and connecting each group to one autopilot port
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* Increase bus speed limit (usually set to 100kHz for external I2C bus)
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- Dividing the devices into groups, each with approximately the same number of devices, and connecting each group to one autopilot port
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- Increase bus speed limit (usually set to 100kHz for external I2C bus)
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### Excessive Wiring Capacitance
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@@ -71,9 +70,10 @@ The electrical capacity of bus wiring increases as more devices/wires are added.
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The problem can be analyzed using an oscilloscope, where we see that the edges of SDA/SCL signals are no longer sharp.
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There are several ways to reduce the problem:
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* Dividing the devices into groups, each with approximately the same number of devices, and connecting each group to one autopilot port
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* Using the shorter and higher quality I2C cables, see the [cable wiring page](../assembly/cable_wiring.md#i2c-cables) for details
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* Separating the devices with a weak open-drain driver to smaller buses with lower capacitance by using [I2C Bus Accelerators](#i2c-bus-accelerators)
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- Dividing the devices into groups, each with approximately the same number of devices, and connecting each group to one autopilot port
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- Using the shorter and higher quality I2C cables, see the [cable wiring page](../assembly/cable_wiring.md#i2c-cables) for details
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- Separating the devices with a weak open-drain driver to smaller buses with lower capacitance by using [I2C Bus Accelerators](#i2c-bus-accelerators)
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## I2C Bus Accelerators
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@@ -81,6 +81,7 @@ I2C bus accelerators are separate circuits that can be used to support longer wi
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They work by physically dividing an I2C network into 2 parts and using their own transistors to amplify I2C signals.
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Available accelerators include:
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- [Thunderfly TFI2CEXT01](https://docs.thunderfly.cz/avionics/TFI2CEXT01/):
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- This has Dronecode connectors and is hence very easy to add to a Pixhawk I2C setup.
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@@ -89,7 +90,7 @@ Available accelerators include:
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### I2C Level Converter function
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Some I2C devices have 5V on the data lines, while the Pixhawk connector standard port expects these lines to be 3.3 V.
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You can use the TFI2CEXT01 as a level converter to connect 5V devices to a Pixhawk I2C port. This feature is possible because the SCL and SDA lines of TFI2CEXT01 are 5V tolerant.
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You can use the TFI2CEXT01 as a level converter to connect 5V devices to a Pixhawk I2C port. This feature is possible because the SCL and SDA lines of TFI2CEXT01 are 5V tolerant.
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## I2C Address Translators
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@@ -112,6 +113,6 @@ Software development for I2C devices is described in [I2C Bus (Development Overv
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## Further Information
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* [I2C](https://en.wikipedia.org/wiki/I%C2%B2C) (Wikipedia)
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* [I2C Comparative Overview](https://learn.sparkfun.com/tutorials/i2c) (learn.sparkfun.com)
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* [Driver Framework](../middleware/drivers.md)
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- [I2C](https://en.wikipedia.org/wiki/I%C2%B2C) (Wikipedia)
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- [I2C Comparative Overview](https://learn.sparkfun.com/tutorials/i2c) (learn.sparkfun.com)
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- [Driver Framework](../middleware/drivers.md)
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@@ -28,7 +28,7 @@ If you need your own value for address translation, changing the configuration r
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## Example of Use
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The tachometer sensor [TFRPM01](../sensor/thunderfly_tachometer.md) can be set to two different addresses using a solder jumper.
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If the autopilot has three buses, only 6 sensors can be connected and no bus remains free (2 available addresses * 3 I2C ports).
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If the autopilot has three buses, only 6 sensors can be connected and no bus remains free (2 available addresses \* 3 I2C ports).
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In some multicopters or VTOL solutions, there is a need to measure the RPM of 8 or more elements.
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The [TFI2CADT01](https://www.tindie.com/products/26353/) is highly recommended in this case.
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@@ -39,7 +39,6 @@ By adding another TFI2CADT01, 4 more devices can be connected to the same bus.
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[](https://mermaid-js.github.io/mermaid-live-editor/edit#pako:eNptkd9rwjAQx_-VcE8dtJB2ukEfBLEWfJCJy8CHvgRznQH7gzSBDfF_33VZB2oCyf3I576XcBc4dgohh08j-xMTRdUyWuX2I6LNErY7zJh0tuv1ubNP_7csSRZsudlHS22GHlGxAduhM3fEfrdNI1GS4emK8a85fwSyGyC9A0S5yVbrg_DZKfLtCxH9JsjhaU7VvI7pfK3_NCg_NXmO3pwl5uYt9D0yAXoWoFNP4yM9H-kspJ0FtF8CdObpURtiaNA0UisaymWsrsCesMEKcnIV1tKdbQVVeyXU9UpaXCttOwO5NQ5jGKf1_t0ep9gzhZY04sYnrz9BI4mU)
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<!-- original mermaid graph
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graph TD
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FMU(FMU - PX4 autopilot)
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@@ -54,7 +53,6 @@ graph TD
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ADT -- > RPM6(Out2: TFRPM01C 0x52 - 0x2e)
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-->
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::: info
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TFI2CADT01 does not contain any I2C buffer or accelerator.
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As it adds additional capacitance on the bus, we advise combining it with some bus booster, e.g. [TFI2CEXT01](https://docs.thunderfly.cz/avionics/TFI2CEXT01/).
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@@ -62,4 +60,4 @@ As it adds additional capacitance on the bus, we advise combining it with some b
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### Other Resources
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* Datasheet of [LTC4317](https://www.analog.com/media/en/technical-documentation/data-sheets/4317fa.pdf)
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- Datasheet of [LTC4317](https://www.analog.com/media/en/technical-documentation/data-sheets/4317fa.pdf)
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