Gathering ROS messages for the Blackboard with different data rates

[valschmidt]

I'm trying to follow the paradigm described in the Data Gathering Tutorial. It's not fully supported yet in the version I'm using, I'm struggling to make it work, and I need some help.

I'm using py_trees v 0.7.6 and py_trees_ros v0.6.1, and I know these are old, but it is what's available via apt for noetic. I realize asking for help for versions that are so dated is asking a lot.

I have three message topics that I want to post to the Blackboard. Two come at 10Hz and the second comes only when the an event is triggered.

One out of the ordinary thing about my setup - I have a new Behavior, ToLocalBlackboard, which inherits from ToBlackboard, and overrides setup() allowing me to replace the blackboard created by ToBlackboard and pass in my own in instead. This allows me to create a single globally accessible blackboard. I did this because the blackboard Client method is not yet supported and I didn't see another way to access it.

Anyway, here's the setup:

root = py_trees.composites.Parallel(
      name="Mesobot",
      policy = py_trees.common.ParallelPolicy.SUCCESS_ON_ALL
  )

data2bb = py_trees.composites.Parallel(
  name = "Data2BB",
  memory=False,
  policy=py_trees.common.ParallelPolicy.SUCCESS_ON_ALL
)

# Comes only episodically
behavior2BB = ToLocalBlackboard(
  name="behaviorparam2BB",
  topic_name="/ben/project11/behaviors/mesobot/input",
  topic_type = BehaviorInformation,
  blackboard_variables={'behavior': None},
  blackboard = bhv_bb
)

# Comes at 10 Hz.
asvpos2BB = ToLocalBlackboard(
  name="ASVData2BB",
  topic_name="/ben/project11/odom",
  topic_type=Odometry,
  blackboard_variables={'asv_pos': None},
  blackboard = bhv_bb
)
# Comes at 10 Hz.
mesobotpos2BB = ToLocalBlackboard(
  name="MesobotData2BB",
  topic_name="/mesobot/project11/odom",  
  topic_type=Odometry,
  blackboard_variables={'mesobot_pos': None},
  blackboard=bhv_bb
)

root.add_children([data2bb,Enable,OperationalSelector])
data2bb.add_children([behavior2BB, asvpos2BB,mesobotpos2BB])

This looks something like this:

Mesobot
[‖] Data2BB
    --> behaviorparam2BB
    --> ASVData2BB
    --> MesobotData2BB
--> Enabled?
[o] Operational

My first question, in the example in the tutorial the battery2bb element is a Sequence. Why? When ToBlackboard.update() doesn't have a message it returns RUNNING. Doesn't this block, and so won't battery2bb block until messages are received on all topics? To try to prevent this, my Data2BB element is a Parallel composite. I'm not sure it's working how I hoped.

But in any case, I find that if the slow data rate topic is listed first in the Data2BB sequence like this:
data2bb.add_children([behavior2BB, asvpos2BB,mesobotpos2BB])
I never get data from any of the topics into the bulletin board. If I put it last, like this:
data2bb.add_children([asvpos2BB,mesobotpos2BB, behavior2BB])
I get data from the other two higher rate topics, but I never see any data at all from the slow rate topic. And if I remove the higher rate topics altogether, like this:
data2bb.add_children([behavior2BB])
the slow data rate topics comes through ok.

How should I architect this so that all messages populate the blackboard all the time?