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FreeRTOS+ WolfSSL Demo
An executable example

Download

The example presented on this page is available in the following directory of the offical FreeRTOS zip file download:
FreeRTOS-Plus/Demo/FreeRTOS_Plus_WolfSSL_Windows_Simulator


Introduction

The project presented on this page demonstrates WolfSSL being used to secure communication between a TCP/IP client and a TCP/IP server.


Hardware setup

The demo uses the FreeRTOS Windows simulator. The simulator provides an extremely convenient self contained evaluation environment because it can be built using Microsoft's free Visual C++ Express tools, and it removes the need to use any external hardware. However, unlike when using a real FreeRTOS port, the FreeRTOS Windows simulator port does not exhibit real time behaviour.

As the FreeRTOS simulator runs in a Windows environment, the demo application also has access to, and therefore uses, the Windows TCP/IP stack and Windows loopback virtual network interface. Using the loopback interface allows the project to be used without a live network connection.

Although this demo application does not require any custom TCP/IP functionality to be included in the build, it is generally very easy to run WolfSSL on top of a popular (eg. lwIP) or custom TCP/IP stack, or other transport medium (eg. Bluetooth). WolfSSL offers an easy-to-use I/O abstraction layer allowing the user to write their own custom Input/Output functions.

Provided the application is executed on a standard Windows computer, no external hardware is necessary, and no hardware setup is necessary.


The TCP/IP server task

The FreeRTOS TCP/IP server task is implemented in the SecureTCPServerTask.c source file. It creates a TCP/IP socket that is configured to listen for connections from the FreeRTOS TCP/IP client task. After accepting a connection, the TCP/IP server task simply writes all the data it receives through the socket to the console until the connection is closed.

A WolfSSL object is created each time a connection is accepted, and deleted each time a connection is closed.

The server behaviour is depicted in the flowchart below.

A flowchart showing the behaviour of the RTOS TCP/IP server task
The behaviour of the RTOS server task


The TCP/IP client task

The FreeRTOS TCP/IP client task is implemented in the SecureTCPClientTask.c source file. It creates a TCP/IP socket, then repeatedly connects the socket to the FreeRTOS TCP/IP server task, sends ten strings through the socket, before closing the socket again. A short delay is used between each iteration to prevent the server task writing to the console too quickly.

A WolfSSL object is created each time the socket is connected, and deleted each time the socket is closed.

The client behaviour is depicted in the flow chart below.

A flowchart showing the behaviour of the RTOS TCP/IP client task
The behaviour of the RTOS client task


Building and executing the demo

  1. Ensure Microsoft Visual C++ is installed. The free Express version can be used.

  2. The Visual C++ solution file is called FreeRTOS_Plus_WolfSSL.sln, and is located in the \FreeRTOS-Plus\Demo_Projects_Using_FreeRTOS_Simulator\FreeRTOS_Plus_WolfSSL directory of the download. Double click the file to open Visual C++, or alternatively open the file from within the Visual C++ IDE.

    The RTOS project viewed inside the compiler development tool
    The RTOS project viewed in the Visual C++ IDE
    Within the solution explorer:
    • The source files that implement the demo application are listed in the Demo App Source folder.
    • The source files that implement the encryption functionality are listed in the FreeRTOS+/WolfSSL folder.
    • The source files that implement the RTOS functionality are listed in the FreeRTOS folder.

  3. Build and execute the application.

    The output generated when the RTOS tasks execute
    The output generated when the demo application executes




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