Defining Types

Background

In F Prime, a type definition defines a kind of data that you can pass between components or use in commands and telemetry.

For this tutorial, you need one type definition. The type will define an enumeration called MathOp, which represents a mathematical operation.

In this section

In this section, you will create a Types directory and add it to the project build. You will create an enumeration to represent several mathematical operations.

Setup

To start, create a directory where your type(s) will live:

# In: MathProject 
mkdir Types 
cd Types

The user defines types in an fpp (F prime prime) file. Use the the command below to create an empty fpp file to define the MathOp type:

# In: Types
touch MathTypes.fpp

Here you have created an empty fpp file named MathTypes in the Types directory.

Implementing the Types

Use your favorite text editor, visual studios, nano, vim, etc…, and add the following to MathTypes.fpp.

# In: MathTypes.fpp
module MathModule { 

    @ Math operations
    enum MathOp {
        ADD @< Addition
        SUB @< Subtraction
        MUL @< Multiplication
        DIV @< Division
  }
}

Important note: think of modules similar to a cpp namespace. Whenever you want to make use of the enumeration, MathOp, you will need to use the MathModule module.

Above you have created an enumeration of the four math types that are used in this tutorial.

Adding to the Build

To specify how MathTypes.fpp should build with the project, you need to make two modifications to the MathProject:

1. Create and edit CMakeLists.txt in Types to include MathTypes.fpp into the build.

To create CMakeLists.txt use:

# In: Types
touch CMakeLists.txt 

Note: capitalization and spelling is important when creating files!

Use a text editor to replace whatever is in CMakeLists.txt, most likely nothing, with the following.

set(SOURCE_FILES
  "${CMAKE_CURRENT_LIST_DIR}/MathTypes.fpp"
)

register_fprime_module()

1. Add the Types directory to the overall project build by adding to project.cmake.

Edit project.cmake, located in the MathProject directory, and add the following line at the end of the file:

# In: MathProject/project.cmake
add_fprime_subdirectory("${CMAKE_CURRENT_LIST_DIR}/Types/")

The Types directory should now build without any issues. Test the build with the following command before moving forward.

# In: Types 
fprime-util build 

Note: if you have not generated a build cache already, you may need to run fprime-util generate before you can build.

The output should indicate that the model built without any errors. If not, try to identify and correct what is wrong, either by deciphering the error output, or by going over the steps again. If you get stuck, you can look at the reference implementation.

The advanced user may want to go inspect the generated code. Go to the directory MathProject/build-fprime-automatic-native/MathTypes. The directory build-fprime-automatic-native is where all the generated code lives for the “automatic native” build of the project. Within that directory is a directory tree that mirrors the project structure. In particular, build-fprime-automatic-native/MathTypes contains the generated code for MathTypes. The files MathOpEnumAc.hpp and MathOpEnumAc.cpp are the auto-generated C++ files corresponding to the MathOp enum. You may wish to study the file MathOpEnumAc.hpp. This file gives the interface to the C++ class MathModule::MathOp. All enum types have a similar auto-generated class interface.

Summary

At this point you have successfully created the MathOp type and added it to the project build. You can add more types here later if you feel so inclined.

Next: Constructing Ports