Add per board/target dds_topics.yaml configuration for uXRCE

[AlexisTM]

Solved Problem

• The uXRCE configuration is buried deep within the code.
• Changing the uXRCE configuration board/target changes it for every single board.

Solution

• Keep the default configuration in the module
• Add a per target dds_config.yaml file

The selection goes as, for example make px4_fmu-v6x_rover

• Use the target file (boards/px4/fmu-v6x/rover_dds_topics.yaml)
• If not available, use the default target board file (boards/px4/fmu-v6x/default_dds_topics.yaml)
• If not available, use the module file (src/modules/uxrce_dds_client/dds_topics.yaml)

Changelog Entry

For release notes:

Feature New per board/target configuration file for uXRCE 
Use: `boards/{vendor}/{board}/{target}_dds_topics.yaml`

[dagar]

I'm certainly in favor of having customization mechanisms (for custom projects, etc), but at the moment I'm not a fan of it differing just for v6x like this.

I think what we really need here is runtime configurability.

[AlexisTM]

In this case, the v6x variant is only there as an example. It doesn't have to be within the PR at all.

Runtime configuration would mean we would need to build & assign a topic to all uOrb topics. That would be close to 230 messages, each to 1+ topics.

How would you see runtime configurability?

[dagar]

In this case, the v6x variant is only there as an example. It doesn't have to be within the PR at all.

Thanks, I just want to be careful to keep things as consistent as possible between targets and avoid future surprises when those files inevitably diverge.

Runtime configuration would mean we would need to build & assign a topic to all uOrb topics. That would be close to 230 messages, each to 1+ topics.

Yes that's one issue, we likely need both build time and runtime configurability (for the included subset that's actually in the build).

One possible baby step is to start with a few presets (like mavlink modes) so at least we can get past trying to please everyone with radically different requirements.

[dagar]

Another idea that just occurred to me regarding overriding the built in dds_topics.yaml would be to allow specifying that file in kconfig. Then the default would simply be src/modules/uxrce_dds_client/dds_topics.yaml.

For example here's how a board can set a custom mavlink dialect.

PX4-Autopilot/src/modules/mavlink/Kconfig

Line 7 in ba75b9c

menuconfig MAVLINK_DIALECT

PX4-Autopilot/src/modules/mavlink/CMakeLists.txt

Lines 60 to 79 in ba75b9c

	add_custom_command(
	OUTPUT ${MAVLINK_LIBRARY_DIR}/${CONFIG_MAVLINK_DIALECT}/${CONFIG_MAVLINK_DIALECT}.h
	COMMAND
	${PYTHON_EXECUTABLE} ${MAVLINK_GIT_DIR}/pymavlink/tools/mavgen.py
	--lang C --wire-protocol 2.0
	--output ${MAVLINK_LIBRARY_DIR}
	${MAVLINK_GIT_DIR}/message_definitions/v1.0/${CONFIG_MAVLINK_DIALECT}.xml > ${CMAKE_CURRENT_BINARY_DIR}/mavgen_${CONFIG_MAVLINK_DIALECT}.log
	DEPENDS
	git_mavlink_v2
	${MAVLINK_GIT_DIR}/pymavlink/tools/mavgen.py
	${MAVLINK_GIT_DIR}/message_definitions/v1.0/${CONFIG_MAVLINK_DIALECT}.xml
	${BOARD_DEFCONFIG}
	# generate after uAvionix
	mavlink_c_generate_uavionix
	${MAVLINK_LIBRARY_DIR}/${MAVLINK_DIALECT_UAVIONIX}/${MAVLINK_DIALECT_UAVIONIX}.h
	COMMENT "Generating Mavlink ${CONFIG_MAVLINK_DIALECT}: ${MAVLINK_GIT_DIR_RELATIVE}/message_definitions/v1.0/${CONFIG_MAVLINK_DIALECT}.xml"
	)
	add_custom_target(mavlink_c_generate DEPENDS ${MAVLINK_LIBRARY_DIR}/${CONFIG_MAVLINK_DIALECT}/${CONFIG_MAVLINK_DIALECT}.h)

[PetervdPerk-NXP]

In this case, the v6x variant is only there as an example. It doesn't have to be within the PR at all.
Runtime configuration would mean we would need to build & assign a topic to all uOrb topics. That would be close to 230 messages, each to 1+ topics.
How would you see runtime configurability?

You could take a look on how it's done for Zenoh, there it's both compile-time (generating serializers and datatypes) and runtime mapping datatypes/topics to zenoh (ros2) topic.s

[AlexisTM]

Or Mavlink's way: Configure the streams according to different default configurations.

I am a bit worried on the amount of work the runtime mapping will take, in comparison to 7 lines.

[dagar]

Or Mavlink's way: Configure the streams according to different default configurations.

I am a bit worried on the amount of work the runtime mapping will take, in comparison to 7 lines.

It's not one extreme or the other, first we can add this simple build time override mechanism immediately if it's actually helpful. I just don't want to carry an fmu-v6x difference that will likely diverge over time.

I'm suggesting the runtime configurability because there are a few common cases that cover the vast majority. Some people/projects will want to fully customize data flow in each direction (custom dds_topics.yaml), but most won't want to or need to with a few presets.

[AlexisTM]

Indeed. I removed the example, as it is not required.