Cakem1x
commented
7 months ago I think this would be a very nice tool to have. I also had exactly the same name like you in mind for it (priority mux), when searching for it. Have you made any (public) progress on this somewhere?
My use-case would be similar to what the cmd_vel_mux does, but I need to be able to "priority mux" both TwistStamped msgs and FourWheelSteeringMsgs. I use a controller that supports both Twist msgs (widespread) and FourWheelSteeringMsgs (supports more fine-graned control of wheels, e.g. change wheel orientation without moving the base).
However, I think supporting two (or, generally, more than one) input types is probably a bit cumbersome to implement. And I am not sure if that use-case is common enough to warrant a generic implementation.
mllofriu
Description
Implement a priority multiplexer like cmd_vel_mux (https://github.com/kobuki-base/cmd_vel_mux/blob/devel/src/cmd_vel_mux.cpp) for generic topic types. The multiplexer would give preference to the highest priority topic that published within a given time window, suppressing all other topics.
Note that this tool would replace cmd_vel_mux, but allow for uses with other topic types.
We are currently pursuing the implementation of input/output suppressors/inhibitors, as described in the subsumtion architecture, as described in here:
https://people.csail.mit.edu/brooks/papers/AIM-864.pdf
This other paper claims to have implemented it in ROS (1) but no source is available:
file:///home/mllofriu/Downloads/Subsumption%20Model%20Implemented%20on%20ROS%20for%20Mobile%20Robots%20_Li16.pdf
Completion Criteria
A new tool, say priority_mux, is implemented.
It allows to specify a list of topics of a generic, but equal, type. The order in which topics are published determines their relative priority, the first one being the highest priority one.
It contains a parameter that specifies the length of the time window, T, in seconds. Once an input topic publishes a message which is forwarded by the multiplexer, all lower priority topics will be suppressed for T seconds. Any topics with a higher priority topics, however, can be forwarded right away.
Implementation Notes / Suggestions
The feature could be implemented by combining features from topic_tools/mux and cmd_vel_mux. The services and selection logic can be stripped from mux, and the time window logic can be migrated from cmd_vel_mux.
We can certainly help implement or implement it. We just wanted to check if it is something this team would be interested in incorporating to topic_tools. As well as to check if you maybe know any other existing tool that can be used for this purpose.