Constructing Ports

Background

A port is the endpoint of a connection between two components. A port definition is like a function signature; it defines the type of the data carried on a port.

Requirements

For this tutorial, you will need two port definitions:

• OpRequest for sending an arithmetic operation request from MathSender to MathReceiver.

• MathResult for sending the result of an arithmetic operation from MathReceiver to MathSender.

In this section

In this section, you will create a Ports directory where you will create two ports in MathPorts.fpp. You will add the ports directory into the project build and built Ports.

Setup

Start by making a directory where the ports will be defined. Create a directory called Ports in the MathProject directory:

# In: MathProject
mkdir Ports 
cd Ports

While in “Ports”, create an empty fpp file called MathPorts.fpp, this is where the ports will be defined:

# In: Ports
touch MathPorts.fpp

Implementing the Ports

Use your favorite text editor to add the following to MathPorts.fpp:

# In: MathPorts.fpp
module MathModule { 
  @ Port for requesting an operation on two numbers
  port OpRequest(
    val1: F32 @< The first operand
    op: MathOp @< The operation
    val2: F32 @< The second operand
  )

  @ Port for returning the result of a math operation
  port MathResult(
    result: F32 @< the result of the operation
  )
}

Notice how we define ports in MathModule, which is where we defined MathOp as well.

Here, you have created two ports. The first port, called OpRequest, carries two 32-bit floats (val1 and val2) and a math operations op. The second port only carries one 32-bit float (result). The first port is intended to send an operation and operands to the MathReceiver. The second port is designed to send the results of the operation back to MathSender.

For more information about port definitions, see The FPP User’s Guide.

Adding to the Build

Create a CMakeLists.txt file in Ports.

# In: Ports
touch CMakeLists.txt

Add the following to the CMakeLists.txt.

# In: Ports/CMakeLists.txt
set(SOURCE_FILES
  "${CMAKE_CURRENT_LIST_DIR}/MathPorts.fpp"
)

register_fprime_module()

Add the following to project.cmake. Remember that project.cmake is in MathProject, not Ports.

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

Ports should build without any issues. Use the following to build:

# In: Ports
fprime-util build

Check in MathProject/build-fprime-automatic-native/MathPorts for port definitions. The names of the auto-generated C++ files end in *PortAc.hpp and *PortAc.cpp. Note however, the auto-generated C++ port files are used by the autocoded component implementations; you won’t ever program directly against their interfaces.

Conclusion

At this point, you have successfully implemented all the ports used for this tutorial and added them to the build.

Next: Creating Components Part 1: Creating the MathSender