AP_DDS: add param DDS_DOMAIN_ID

[srmainwaring]

Add a param DDS_DOMAIN_ID.

This allows the ROS_DOMAIN_ID to be set to values other than the current default of 0, useful for managing multiple vehicles or keeping various ROS 2 running instances separated. The behaviour is backward compatible with a default of 0.

The range of valid domain ids is 0 to 232 (see: https://docs.ros.org/en/rolling/Concepts/About-Domain-ID.html)

Comment: the param should really be ROS_DOMAIN_ID to be consistent with usage with the ros2 cli, but as it's in the DDS_ param tree the name DDS_ROS_DOMAIN_ID would just be confusing.

Testing

Run the default UDP instance:

ros2 launch ardupilot_sitl sitl_dds_udp.launch.py transport:=udp4 synthetic_clock:=True wipe:=False model:=quad speedup:=1 slave:=0 instance:=0 defaults:=$(ros2 pkg prefix ardupilot_sitl)/share/ardupilot_sitl/config/default_params/copter.parm,$(ros2 pkg prefix ardupilot_sitl)/share/ardupilot_sitl/config/default_params/dds_udp.parm sim_address:=127.0.0.1 master:=tcp:127.0.0.1:5760 sitl:=127.0.0.1:5501

In a separate terminal start mavproxy and set the DDS_DOMAIN_ID to a different value:

$ mavproxy.py --master 127.0.0.1:14550 --console

> param set DDS_DOMAIN_ID 1
> param show DDS*
DDS_DOMAIN_ID    1.0
DDS_ENABLE       1.0         # Enabled
DDS_IP0          127.0
DDS_IP1          0.0
DDS_IP2          0.0
DDS_IP3          1.0
DDS_UDP_PORT     2019.0

Now restart the SITL instance prefixing with the ROS_DOMAIN_ID env variable set

ROS_DOMAIN_ID=1 ros2 launch ardupilot_sitl sitl_dds_udp.launch.py transport:=udp4 synthetic_clock:=True wipe:=False model:=quad speedup:=1 slave:=0 instance:=0 defaults:=$(ros2 pkg prefix ardupilot_sitl)/share/ardupilot_sitl/config/default_params/copter.parm,$(ros2 pkg prefix ardupilot_sitl)/share/ardupilot_sitl/config/default_params/dds_udp.parm sim_address:=127.0.0.1 master:=tcp:127.0.0.1:5760 sitl:=127.0.0.1:5501

Use the ros2 cli to inspect nodes:

# expect no nodes, as the default domain is 0
$ ros2 node list

# expect the ardupilot node in domain 1
$ ROS_DOMAIN_ID=1 ros2 node list
/ardupilot_dds

[Ryanf55]

Awesome, love it. Thanks!

Can we add a wiki change to mention the param?

[rmackay9]

this has been included in Copter-4.5.7-beta1 as part of PR #27919