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

Ensure Microsoft Visual C++ is installed. The free Express version can be used.
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 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.
Build and execute the application.

The output generated when the demo application executes