Coordinating State Machines with Signal Events

Overview

Similarly to call events, which you learned about in the previous tutorial, signal events enable state machines to interact with each other. Signal events, however, are less direct: they trigger in response to a signal from another state machine instead of being called directly by that state machine. Additionally, these signals can only be sent in a Behavior Execution Engine simulation from within the delegate code. In this section, you will replace the ground station's call to shutdown the UAV with a signal event.

This section covers the following concepts:

• Signal events
• The Behavior Execution Engine StateMachineRemoteControl

public void sendShutDownSignal(UAV target) {
    mStateMachineRemoteControl.sendSignalEvent("Simulation::ShutDown", target);
}

Figure A1: Sending a signal event from a delegate

Prerequisites

Instructions

Replace the call event with the signal event

1. Open the UAVMission.mdzip project from the previous section.
2. In the Containment Tree, right-click the Simulation package and select Create Element (or press CtrlShiftE).
3. Select Signal and enter ShutDown as its name.
4. In the UAV State Machine diagram, double-click the transition going from the TransmittingData state to the final state.
5. In the Trigger category, set the Event Type to SignalEvent.
6. Set the Signal to ShutDown and click Close.

Replace the call with the signal

1. In the System Definition (the BDD), select the GroundStation block, click the Create Element button () on the upper-right corner of the block, and select Operation.
2. Enter sendShutDownSignal( target : UAV ) as the operation's name and parameter.
3. Double-click the new operation, set the Visibility to private, and click Close.
4. In the GroundStation State Machine diagram, double-click the transition going from the ReceivingSensorData state to the final state.
5. In the Effect category, set the Body and Language to the string sendShutDownSignal(uav);, (optionally) add a line break before sendShutDownSignal(uav);, and click Close.

Add the supporting delegate code

You can use the StateMachineRemoteControl dependency from the analysis tool controller to send a signal to another state machine, triggering any signal events that expect that signal.

1. In the GroundStationDelegate class, add the following import statement:

   import com.agi.moxie.api.StateMachineRemoteControl;

2. Add the following private field:

   private StateMachineRemoteControl mStateMachineRemoteControl;

3. Add the following dependency injection and field initialization in the constructor:

   public GroundStationDelegate( ...
           @InjectByName("stateMachineRemoteControl") StateMachineRemoteControl stateMachineRemoteControl,
            ... ) {
      mStateMachineRemoteControl = stateMachineRemoteControl;
       ...
   }

4. Create the following public method:

   public void sendShutDownSignal(UAV target) {
       mStateMachineRemoteControl.sendSignalEvent("Simulation::ShutDown", target);
   }

5. Save your work and reinstall the delegate module.
6. Execute the simulation and look in the state history trace to observe that the UAV still shuts down (reaches its final state) at the end of the simulation.