Communication of ROS2 with the DDS-Space/RTPS

asked 2018-10-23 05:02:40 -0500

ToRaVe gravatar image

updated 2018-10-23 05:40:55 -0500

I try to set up a communication between ROS2 and C-based RTPS-Stack. That way, I want to exchange information.

How I try:

In ROS2, I have defined a my_msg_type.msg, which consists of a single float. The file looks like this:

float32 f_time_stamp

and that's it. Based on this, I implemented a simple Publisher and a Subscriber and gave them a topic name: my_topic. They work perfectly fine together. ROS2 is - as far as i know - running on default settings, so it should be using the rmw_fastrtps_cpp middleware implementation.

On the opposite end, I am using the Micro-XRCE-DDS-Client ( ) in combination with the Micro-XRCE-DDS-Agent ( ), which are supposed to work together. Here I defined my message type in an .idl, which looks like this:

struct my_msg_type { float f_time_stamp; };

From this, I built simple Publishers and Subscribers, using Micro-XRCE-DDS-Agent ( ). I adjusted the topic and message type according to the ROS2 mappings to rt/my_topic and my_pkg/my_msg_type respectively. They also work perfectly well together and all data sent by the publisher reaches the subscriber.

What doesn't work:

Now when I am trying to let the Micro-XRCE-DDS Stack communicate with ROS2, both sides seem to have problems. When I try to listen to the topic using ros2 topic echo /my_topic, it says

Cannot echo topic '/my_topic', as it contains more than one type: [my_pkg/my_msg_type, my_pkg/my_msg_type]

So I guess that I must have gone wrong somewhere in the type definitions or that they are changing somewhere on their journey.

The header-file produced from my .msg in ROS2 contains

typedef struct my_pkg__msg__my_msg_type { float f_time_stamp; } my_pkg__msg__my_msg_type;

while the header-file produced by the Micro-XRCE-DDS-Agent contains

typedef struct my_msg_type { float f_time_stamp; } my_msg_type;

I tried changing the struct's name in the latter header-file, so it reads the same as in the header produced by ROS2, but it changed nothing on the behaviour.

Any help and idea is greatly appreciated

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So I guess that I must have f* up somewhere [..]


gvdhoorn gravatar image gvdhoorn  ( 2018-10-23 05:17:37 -0500 )edit


Have you, or has anyone else reading this, been able to find a solution for this type of communication between ROS2 and DDS and can point me in the right direction?

rhogan gravatar image rhogan  ( 2019-10-03 16:08:19 -0500 )edit