uORB Write Module Documentation

Toolbox: uORB Read and Write

Introduction

One-sentence Description: A uORB data publishing interface module for publishing messages of a specified format to PX4 uORB topics.

This module belongs to the RflySim toolchain’s uORB communication interface library. It enables users to publish custom computation results or control data—formatted according to PX4 uORB message specifications—to corresponding topics within the Simulink simulation environment. The module supports configurable input ports, allowing it to match the field structure of any predefined uORB topic; during code generation, the corresponding uORB topic definition file is automatically included.

Typical applications include user-defined flight control algorithm development. When used in conjunction with the uORB Read module, it facilitates uORB message exchange between Simulink-level algorithms and the PX4 flight control stack, enabling co-simulation with CopterSim, RflySim3D, and PX4. Users can directly publish custom messages to the PX4 flight controller, thereby simulating and validating custom control logic.

Port Descriptions

Input Ports (Inputs)

The input ports of this module are dynamically generated based on the configuration in the uORB Parameter Names and Data Type region. Each port corresponds to a message field of the uORB topic. A typical configuration format is as follows:

Port Name	Data Type	Dimension	Description
Custom Field Name	User-specified	User-specified	Value of the corresponding field in the uORB message to be published

Output Ports (Outputs)

This module has no output ports.

Parameter Configuration (Parameters)

The following parameters can be configured in the Mask dialog box opened by double-clicking the module:

Parameter Name	Type	Default Value	Available Values/Range	Description
uORB Topic	string	vehicle_attitude	Any valid uORB topic name	Name of the uORB topic to which the message will be published
uORB Parameter Names and Data Type	Table configuration	Empty	-	Configure the names, data types, and dimensions of all message fields to be published
Sample time (s)	double	0.01	>0	Module sampling time

Parameter Configuration Details

uORB Topic

Specifies the name of the uORB topic to which the message will be published. The name must exactly match the filename (excluding the .msg extension) of a topic definition file in the PX4 firmware’s msg directory. Click the Open.msg file button to view the field requirements of the currently selected topic’s definition file, or click Open.msg folder to open the folder containing all defined uORB topics.

uORB Parameter Names and Data Type

This region uses a table to configure all message fields to be published; each row corresponds to one input port:

• Name: Must exactly match the field name in the topic’s .msg definition file.
• Data Type: Must match the data type of the corresponding field in the topic’s .msg definition file. Supported types include double, single, int8, int16, int32, etc.
• Dimension: Must match the dimension of the corresponding field in the topic’s .msg definition file. Enter 1 for scalars, or the array length for arrays.

Sample time (s)

Specifies the sampling interval (in seconds) at which the module publishes messages to uORB.

Module Characteristics (Block Characteristics)

Characteristic	Value
Supported Data Types	double, single, int8, int16, int32, uint8, uint16, uint32, etc.
Direct Feedthrough	Yes
Sample Time	Discrete
Code Generation Support	Yes

Data Communication Protocol

This module does not involve network communication.

Related Modules

Module Name	Description
uORB Read	Reads message data from a specified uORB topic and outputs each field to corresponding ports

Usage Example

For usage examples, refer to the following path:

[RflySim Installation Path]/RflySimAPIs/5.RflySimFlyCtrl/0.ApiExps/7.uORB-Read-Write/Readme.pdf

Please consult Readme.pdf in the above path for complete example descriptions and step-by-step instructions.

Notes and Common Issues

• Initialization Order: This module must run only after the RflySim initialization configuration module has completed initialization. Do not connect the uORB Write module’s inputs/outputs directly to logic preceding PX4 flight controller startup; otherwise, topic registration may fail and message publishing may become ineffective.
• Topic Definition Matching: The specified uORB Topic name must exactly match the topic name defined in the PX4 firmware msg directory. Each input port’s field name, data type, and dimension configured in the module must precisely match the corresponding fields in the topic’s .msg definition file; otherwise, compilation errors or anomalous message publishing may occur.
• Custom Topic Handling: If using a newly added custom uORB topic, first place the custom .msg file into the PX4 firmware’s msg directory, recompile the PX4 firmware, and refresh it before the module can recognize and use the custom topic. Otherwise, the custom topic definition will not load.
• Sample Time Matching: The configured module sample time should match the update frequency of the corresponding uORB topic. Avoid setting a sample time significantly longer than the topic’s designed update frequency to prevent unnecessary resource consumption. When used with the uORB Read module, ensure both modules’ sample times align with application requirements to avoid data publishing and reading synchronization issues.
• Duplicate Publishing: Do not add multiple uORB Write modules in the same Simulink model to publish data to the same uORB topic simultaneously; this will cause topic data conflicts and unpredictable read/write errors.

Changelog

• v4.20 (2024-08-09): Initial release. Provides basic uORB topic message publishing functionality with support for configurable input ports mapping to uORB message fields.