Advanced: Redirecting Module Output to Stand-Alone Message#

Consider a more advanced Basilisk simulation setup where you have two modules that both need to write to the same stand-alone message. The motivation here is to simultaneously run two or more flight guidance algorithm modules, but only one gets executed depending on the flight mode. Regardless of which guidance module is executed, the guidance output message must be fed to the same control module. This cannot be accomplished if the third module subscribes either to the output message of module 1 or 2. To avoid trying to re-subscribe to different module output messages when switching flight modes, we can choose to have both modules 1 and 2 write to the same stand-alone message as illustrated below.

The benefit is that the 3rd module can subscribe its input message to this one stand-alone message. To be clear, this sample application assumes either module 1 or 2 is executed, but not both. Otherwise, one would overwrite the others’ message output.

The sample simulation script creates two modules which have their individual output messages redirected to a stand-alone message.

In the following sample code, two modules are created. To create a stand-alone message, assume a message of type SomeMsg needs to be created. This is done using:

standAloneMsg = messaging.SomeMsg()

To redirect the output of a module someModule to this stand-alone message, simply set:

someModule.dataOutMsg = standAloneMsg

from Basilisk.architecture import messaging
from Basilisk.moduleTemplates import cppModuleTemplate
from Basilisk.utilities import SimulationBaseClass
from Basilisk.utilities import macros


def run():
    """
    Illustration of re-directing module output message to stand-alone messages
    """

    #  Create a sim module as an empty container
    scSim = SimulationBaseClass.SimBaseClass()

    #  create the simulation process
    dynProcess = scSim.CreateNewProcess("dynamicsProcess")

    # create the dynamics task and specify the integration update time
    dynProcess.addTask(scSim.CreateNewTask("dynamicsTask", macros.sec2nano(1.)))

    # create modules
    mod2 = cppModuleTemplate.CppModuleTemplate()
    mod2.modelTag = "cppModule2"
    scSim.AddModelToTask("dynamicsTask", mod2)

    # create stand-along message with a C++ interface and re-direct
    # the C++ module output message writing to this stand-alone message
    cppMsg = messaging.ModuleTemplateMsg()
    mod2.dataOutMsg = cppMsg

    #  initialize Simulation:
    scSim.InitializeSimulation()

    #   configure a simulation stop time and execute the simulation run
    scSim.ConfigureStopTime(macros.sec2nano(1.0))
    scSim.ExecuteSimulation()

    # read the message values and print them to the terminal
    print("mod2.dataOutMsg:")
    print(mod2.dataOutMsg.read().dataVector)
    print("cppMsg:")
    print(cppMsg.read().dataVector)

    return


if __name__ == "__main__":
    run()

Note

In C++, we are setting standAloneMsg equal to someModule.dataOutMsg. Recording either one will give the same result. Be sure to record standAloneMsg to ensure you capture the redirected message output.

To see the message states of both the module internal message objects and the stand-alone messages, the sample script shows how to use .read() to read the current state of the message object. This will return a copy of the message payload structure.

After executing the script you should see the following terminal output:

source/codeSamples % python bsk-7.py
BSK_INFORMATION: Variable dummy set to 0.000000 in reset.
BSK_INFORMATION: Variable dummy set to 0.000000 in reset.
BSK_INFORMATION: Module ID 1 ran Update at 0.000000s
BSK_INFORMATION: Module ID 2 ran Update at 0.000000s
BSK_INFORMATION: Module ID 1 ran Update at 1.000000s
BSK_INFORMATION: Module ID 2 ran Update at 1.000000s
mod1.dataOutMsg:
[2.0, 0.0, 0.0]
cppMsg:
[2.0, 0.0, 0.0]
mod2.dataOutMsg:
[2.0, 0.0, 0.0]
cppMsg:
[2.0, 0.0, 0.0]

Advanced: Redirecting Module Output to Stand-Alone Message#

This Page