# Manually Generate Client and Agent Code


This content is out of date due to the replacement of the Fast RTPS Bridge in PX4 main and releases after PX4 v1.13.

This topic shows how to manually generate the code for the client and the agent (instead of automatically generating it when the PX4 firmware is compiled).

The code is generated using the python script: /Tools/generate_microRTPS_bridge.py.


This method should only be used for debugging purposes when creating new messages or if you just want to consume the generated code outside of the PX4 domain. Otherwise please use the normal method explained in PX4-Fast RTPS(DDS) Bridge, which uses the PX4-Autopilot build system.

# Disable automatic bridge code generation

First disable automatic generation of bridge code. Set the variable GENERATE_RTPS_BRIDGE to off in the .cmake file for the target platform:


# Using generate_microRTPS_bridge.py

The generate_microRTPS_bridge tool's command syntax is shown below:

$ cd /path/to/PX4/PX4-Autopilot/msg/tools
$ python generate_microRTPS_bridge.py -h
usage: generate_microRTPS_bridge.py [-h] [-a] [-c] [-i] [-j IDL_DIR] [-m] [-l]
                                    [-t MSGDIR] [-b UORB_TEMPLATES]
                                    [-q URTPS_TEMPLATES] [-y YAML_FILE]
                                    [-p PACKAGE] [-o AGENTDIR] [-u CLIENTDIR]
                                    [-f [FASTRTPSGEN]]
                                    [-g FASTRTPSGEN_INCLUDE]
                                    [-r [ROS2_DISTRO]] [--delete-tree]

optional arguments:
  -h, --help            show this help message and exit
  -a, --agent           Flag for generate the agent, by default is true if -c
                        is not specified
  -c, --client          Flag for generate the client, by default is true if -a
                        is not specified
  -i, --generate-idl    Flag for generate idl files for each msg
  -j IDL_DIR, --idl-dir IDL_DIR
                        IDL files dir
  -m, --mkdir-build     Flag to create 'build' dir
  -l, --generate-cmakelists
                        Flag to generate a CMakeLists.txt file for the micro-
                        RTPS agent
  -t MSGDIR, --topic-msg-dir MSGDIR
                        Topics message, by default using relative path 'msg/'
  -b UORB_TEMPLATES, --uorb-templates-dir UORB_TEMPLATES
                        uORB templates, by default using relative path to
                        msgdir 'templates/uorb_microcdr'
  -q URTPS_TEMPLATES, --urtps-templates-dir URTPS_TEMPLATES
                        uRTPS templates, by default using relative path to
                        msgdir 'templates/urtps'
  -y YAML_FILE, --rtps-ids-file YAML_FILE
                        RTPS msg IDs definition path, by default using
                        relative path to msgdir
  -p PACKAGE, --package PACKAGE
                        Msg package naming, by default px4
  -o AGENTDIR, --agent-outdir AGENTDIR
                        Agent output dir, by default using relative path
  -u CLIENTDIR, --client-outdir CLIENTDIR
                        Client output dir, by default using relative path
  -f [FASTRTPSGEN], --fastrtpsgen-dir [FASTRTPSGEN]
                        fastrtpsgen installation dir, only needed if
                        fastrtpsgen is not in PATH, by default empty
                        directory(ies) to add to preprocessor include paths of
                        fastrtpsgen, by default empty
  -r [ROS2_DISTRO], --ros2-distro [ROS2_DISTRO]
                        ROS 2 distro, only required if generating the agent for
                        usage with ROS 2 nodes, by default empty
  --delete-tree         Delete dir tree output dir(s)

:::caution Using with --delete-tree option erases the content of the CLIENTDIR and the AGENTDIR before creating new files and folders. :::

  • The arguments --send/-s and --receive/-r specify the uORB topics that can be sent/received from PX4. Code will only be generated for specified messages.
  • The output appears in CLIENTDIR (-o src/modules/micrortps_bridge/micrortps_client, by default) and in the AGENTDIR (-u src/modules/micrortps_bridge/micrortps_agent, by default).
  • If no flag -a or -c is specified, both the client and the agent will be generated and installed.
  • The -f option may be needed if Fast DDS was not installed in the default location (-f /path/to/fastdds/installation/bin).

The example below shows how you can generate bridge code to publish/subscribe just the sensor_baro single uORB topic.

$ cd /path/to/PX4/PX4-Autopilot
$ python Tools/generate_microRTPS_bridge.py -s msg/sensor_baro.msg -r msg/sensor_combined.msg

# Generated code

Code is generated for the Client, Agent, CDR serialization/deserialization of uORB messages, and the definition of the associated RTPS messages (IDL files).

Manually generated code for the bridge can be found here (by default):

  • Client: src/modules/micrortps_bridge/micrortps_client/
  • Agent: src/modules/micrortps_bridge/micrortps_agent/

# uORB serialization code

Serialization functions are generated for all the uORB topics as part of the normal PX4 compilation process (and also for manual generation). For example, the following functions would be generated for the sensor_combined.msg:

void serialize_sensor_combined(const struct sensor_combined_s *input, char *output, uint32_t *length, struct microCDR *microCDRWriter);
void deserialize_sensor_combined(struct sensor_combined_s *output, char *input, struct microCDR *microCDRReader);

# RTPS message IDL files

IDL files are generated from the uORB .msg files (for selected uORB topics) in the generation of the bridge. These can be found in: src/modules/micrortps_bridge/micrortps_agent/idl/

Fast DDS uses IDL files to define the structure of RTPS/DDS messages (in this case, RTPS/DDS messages that map to uORB topics). They are used to generate code for the Agent, and Fast DDS applications that need to publish/subscribe to uORB topics.


IDL files are compiled to C++ by the fastrtpsgen tool.

# Verify code generation

You can verify successful code generation by checking that the output directories match the listing shown below (On Linux, the tree command can be used for listing the file structure).

Agent directory:

$ tree src/modules/micrortps_bridge/micrortps_agent
├── build
├── CMakeLists.txt
├── idl
│   ├── sensor_baro_.idl
│   └── sensor_combined_.idl
├── microRTPS_agent.cpp
├── microRTPS_timesync.cpp
├── microRTPS_timesync.h
├── microRTPS_transport.cpp
├── microRTPS_transport.h
├── RtpsTopics.cpp
├── RtpsTopics.h
├── sensor_baro_.cpp
├── sensor_baro_.h
├── sensor_baro_Publisher.cpp
├── sensor_baro_Publisher.h
├── sensor_baro_PubSubTypes.cpp
├── sensor_baro_PubSubTypes.h
├── sensor_combined_.cpp
├── sensor_combined_.h
├── sensor_combined_PubSubTypes.cpp
├── sensor_combined_PubSubTypes.h
├── sensor_combined_Subscriber.cpp
└── sensor_combined_Subscriber.h
 2 directories, 20 files

Client directory:

$ tree src/modules/micrortps_bridge/micrortps_client
├── CMakeLists.txt
├── microRTPS_client.cpp
├── microRTPS_client_dummy.cpp
├── microRTPS_client_main.cpp
├── microRTPS_transport.cpp
└── microRTPS_transport.h
 0 directories, 4 files

# Build and use the code

The manually generated Client code is built and used in exactly the same way as automatically generated Client code.

Specifically, once manually generated, the Client source code is compiled and built into the PX4 Firmware as part of the normal build process. For example, to compile the code and include it in Firmware for NuttX/Pixhawk targets:

make px4_fmu-v4_rtps upload


You must first disable automatic bridge code generation so that the toolchain uses the manually generated source code (and does not attempt to regenerate it).

The manually generated Agent code is also compiled and used in the same way as the automatically generated code. The only difference is that the manually source code is created in src/modules/micrortps_bridge/micrortps_agent instead of build/BUILDPLATFORM/src/modules/micrortps_bridge/micrortps_agent/.