Adding Basilisk Modules

Source Code

The Python code shown below can be downloaded here.

Now that we understand what Basilisk processes (task groups) and tasks are, we can move forward and add modules to a task. The cppModuleTemplate example provides a basic module, that will be used in this discussion. These modules demonstrate how to create a prototypical Basilisk module.

The modules behave identically and are useful here because they print their module ID when executed. This makes it easy to observe the module execution order in the simulation.

Simulation Structure

The following simulation creates a single process called dynamicsProcess and a single 0.2 Hz task called dynamicsTask. As shown above, three instances of cppModuleTemplate are created, named mod1, mod2, and mod3 respectively. Note that in this simulation we want modules 2 and 3 to run first, and module 1 to run last.

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


def run():
    """
    Illustration of adding Basilisk modules to a task
    """

    #  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(5.)))

    # create copies of the Basilisk modules
    mod1 = cppModuleTemplate.CppModuleTemplate()
    mod1.modelTag = "module1"

    mod2 = cppModuleTemplate.CppModuleTemplate()
    mod2.modelTag = "module2"

    mod3 = cppModuleTemplate.CppModuleTemplate()
    mod3.modelTag = "module3"

    scSim.AddModelToTask("dynamicsTask", mod1)
    scSim.AddModelToTask("dynamicsTask", mod2, 10)
    scSim.AddModelToTask("dynamicsTask", mod3, 5)

    #  initialize Simulation:
    scSim.InitializeSimulation()
    print("InitializeSimulation() completed...")

    #   configure a simulation stop time and execute the simulation run
    scSim.ConfigureStopTime(macros.sec2nano(5.0))
    scSim.ExecuteSimulation()

    return


if __name__ == "__main__":
    run()

Adding Modules to a Task

To add a module to the simulation, create an instance and give it a unique name using the modelTag property:

module = someModule.someModule()
module.modelTag = "someModuleName"

For C-modules, the class name and instance name are the same. For C++ modules, the first name is the instance, and the second is the class name (which starts with a capital letter). See the example script for both styles.

Next, add the module to a task using:

scSim.AddModelToTask("taskName", module, priority)

• The first argument is the task name.

• The second is the module instance.

• The third is an optional priority (integer).

Warning

If the priority is not provided, it defaults to -1. This means the module will execute after any modules with assigned priorities, and in the order in which it was added. This behavior is consistent with how processes and tasks are handled.

Module Imports

In the example Python script:

• The module cppModuleTemplate is imported from Basilisk.simulation.

Note

Basilisk assigns unique positive ID numbers to modules upon their creation. In the example simulation, the three modules receive IDs 1, 2, and 3, corresponding to the order of creation.

Execution Priorities

In the script:

• Module1 is added without a priority, so it defaults to -1.

• Module2 and Module3 are given priorities 10 and 5, respectively.

Modules with higher priority values are executed first. This allows for deterministic execution ordering.

Note

A task list can contain C++ and Python-based Basilisk modules simultaneously. Python modules are discussed in pyModules.

Expected Output

When you run the script, you should see terminal output similar to:

source/codeSamples % python3 bsk-2.py
BSK_INFORMATION: Variable dummy set to 0.000000 in reset.
BSK_INFORMATION: Variable dummy set to 0.000000 in reset.
BSK_INFORMATION: Variable dummy set to 0.000000 in reset.
InitializeSimulation() completed...
BSK_INFORMATION: C++ Module ID 2 ran Update at 0.000000s
BSK_INFORMATION: C++ Module ID 3 ran Update at 0.000000s
BSK_INFORMATION: C++ Module ID 1 ran Update at 0.000000s
BSK_INFORMATION: C++ Module ID 2 ran Update at 5.000000s
BSK_INFORMATION: C++ Module ID 3 ran Update at 5.000000s
BSK_INFORMATION: C++ Module ID 1_Update at 5.000000s

The reset() method from cppModuleTemplate prints a statement when a variable is initialized. Since three modules are created, this reset message appears three times—once for each module.

Once scSim.InitializeSimulation() is called, Basilisk begins executing the simulation. The Update() method for each module is called in the order determined by their priorities, and the simulation time is printed each time the module executes. As shown, the desired execution order is achieved based on the set priorities.