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FreeRTOS+UDP was removed from the FreeRTOS kernel download from FreeRTOS V10.1.0. See the FreeRTOS+TCP stack, which can be configured for UDP only use, as an alternative.

Example FreeRTOS+UDP Project
For the FreeRTOS Win32 Simulator

On this page:

Source Code and Project Files

This demo application is available in the following directory of the offical FreeRTOS zip file download:

Target Hardware

The project uses the FreeRTOS Windows simulator. The Windows simulator provides a convenient evaluation platform, but it does not exhibit real time behaviour. Simulated time is much slower than real time.

Compiler / Tool Chain

The project is pre-configured to build with the free Express edition of Microsoft Visual C++ (MSVC). MSVC Express Edition 2010 was used.


The demo includes the following standard demo files:
  1. The two echo client tasks
  2. A command console with IP stack specific commands

The project can optionally be built to also include:

  • Two sets of simple client and server tasks, where the client task sends data to the server task. One set of tasks uses the standard sockets interface. The other set of tasks uses the zero copy sockets interface.

  • Two tasks that demonstrate how to use FreeRTOS_select(). A number of sockets are created and added to a set. One task then blocks on the set while the other task sends data to a (pseudo) random member of the set.

Command Console Input and Output

FreeRTOS+UDP is used to allow the command console to be accessed via a UDP terminal. See the Usage Instructions section below.

Build Instructions

  1. Download the zip file that contains the source code and project files. Extract the zip file into a convenient location, ensuring the directory structure is maintained.

    Note: The directory structure is designed to fit into the standard FreeRTOS .zip file download, making it seem non-optimal when seen in isolation.

  2. Open the Visual Studio solution file FreeRTOS_Plus_UDP_with_CLI.sln from within the Visual Studio IDE. The solution file is located in the "FreeRTOS-Plus/Demo_Projects_Using_FreeRTOS_Simulator/FreeRTOS_Plus_UDP_with_CLI" directory.

  3. The demo uses WinPCap to create a virtual network connection by accessing raw Ethernet data on a real network connection. Many computers have more than one real network port. Set configNETWORK_INTERFACE_TO_USE to tell the demo which real port should be used to create the virtual port.

    configNETWORK_INTERFACE_TO_USE is defined in FreeRTOSConfig.h. Available port numbers are displayed on the console when the application is executed (see the image in the Usage Instructions section below).

  4. Follow the instructions provided on the Echo Client example documentation page to set up an echo server and set the address of the echo server in FreeRTOSConfig.h. Alternatively simple local client and server tasks can be created by setting mainCREATE_SIMPLE_UDP_CLIENT_SERVER_TASKS to 1 in main.c.

  5. The virtual port has its own MAC address. Set the constants configMAC_ADDR0 to configMAC_ADDR5 to ensure the MAC address used by the virtual network connection is unique on the network. The constants are located at the bottom of FreeRTOSConfig.h.

  6. If IP address assignment is managed by a DHCP server then no further configuration is required.

    If IP address assignment is not managed by a DHCP server then set ipconfigUSE_DHCP to 0 in FreeRTOSIPConfig.h, then edit the constants at the bottom of FreeRTOSConfig.h that set the default values for a static IP address, DNS server address, gateway address and netmask to ensure they are valid for the Ethernet network. The IP address will be valid if the first three octets of the IP address match the first three octets of other IP addresses on the same network - each IP address must be unique on the network.

  7. Select "Build Solution" from the IDE's Build menu (or press F7) to build the application.

Debug Instructions

The standard Visual Studio key used to start a debug session and break on entry to main() is F10.

The same host computer is used to build the application, debug the application, and (because the FreeRTOS Win32 simulator is used) run the application. There are no special debugging instructions.

Usage Instructions

  • The UDP/IP Related CLI Commands page contains a video that demonstrates:

    1. Connecting to the FreeRTOS command line interface. This demo uses UDP in place of the demonstrated COM port - see note 1 below.

    2. Viewing the IP address assigned to the target hardware by the DHCP server.

    3. Using the DNS resolver to ping a host name.

    4. Viewing the network traffic between the echo client (the FreeRTOS+UDP application) and the echo server.

  • Note 1: The video shows FreeRTOS+CLI being access through a virtual COM port. This demo connects to FreeRTOS+CLI though a UDP port. Suitable free UDP capable dumb terminal programs include YAT and Hercules.

    To allow a UDP connection to be established the IP address assigned by the DHCP server to the (simulated) target is displayed in the Windows console that opens when the application starts to execute.

    Available Ethernet interfaces and IP address configuration
    The available network interfaces and the configuration obtained
    from a DHCP server shown in the Windows console

    NOTE 2: FreeRTOS+CLI receives commands on UDP port 5001 and sends output to UDP port 5002.

    Configuring UDP settings to send to UDP port 5001 and receive from UDP port 5002
    Configuring the YAT terminal to access the command
    interface running on IP address

    Note 3: Ping replies are also displayed in the Windows console (so replies to ping requests sent through the FreeRTOS+CLI console are display in the Windows console).

    Sending an ICMP echo request
    Using YAT to send an ICMP echo (ping) request. In the FreeRTOS Windows simulator
    environment the ping reply is displayed in the Windows console, not the FreeRTOS console.

  • Increasing the value of echoLOOP_DELAY in TwoEchoClients.c will decrease the amount of network traffic that is generated.

  • The following constants are defined in main.c to allow tasks to be included or excluded from the build:

    /* Set the following constants to 1 or 0 to define which tasks to include and
    exclude. */
    #define mainCREATE_UDP_CLI_TASKS                     1
    #define mainCREATE_UDP_ECHO_TASKS                    1

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