Create, Configure and Bind a TCP Socket
Part of the FreeRTOS+TCP Networking Tutorial

TCP Sockets are:

Created using the FreeRTOS_socket() API function with the xType (second) parameter set to FREERTOS_SOCK_STREAM,
Configured using the FreeRTOS_setsockopt() function,
and bound to a port using the FreeRTOS_bind() function.

If the socket is used to implement a server then call FreeRTOS_listen() to place the socket into the Listening state, and call FreeRTOS_accept() to accept incoming connections. Source code examples are provided on this page.

To change the size of the receive and send buffers used by the TCP socket from their defaults call FreeRTOS_setsockopt() using the FREERTOS_SO_RCVBUF and FREERTOS_SO_SNDBUF parameters respectively. This must be done immediately after the socket is created, before it is connected.

If ipconfigUSE_TCP_WIN is set to 1 in FreeRTOSIPConfig.h then the socket will use a sliding window to minimise overhead and maximise throughput. The size of the sliding window can be changed from its default using the FREERTOS_SO_WIN_PROPERTIES parameter to FreeRTOS_setsockopt(). The sliding window size is specified in units of MSS (so if the MSS is set to 200 bytes then a sliding window size of 2 is equal to 400 bytes) and must always be smaller than or equal to the size of the internal buffers in both directions.

By default a child socket is automatically created to handle any connections accepted on a listening TCP/IP socket (the default behaviour can be changed using the FREERTOS_SO_REUSE_LISTEN_SOCKET parameter in a call to FreeRTOS_setsockopt()). Child sockets inherit the buffer sizes and sliding window sizes of their parent sockets.

The first example below demonstrates how to create, configure and bind a client socket. The second example below demonstrates how to create, configure, and bind a server socket, then how to accept new connections on the server socket.


void vCreateTCPClientSocket( void )
{
Socket_t xClientSocket;
socklen_t xSize = sizeof( freertos_sockaddr );
static const TickType_t xTimeOut = pdMS_TO_TICKS( 2000 );

    /* Attempt to open the socket. */
    xClientSocket = FreeRTOS_socket( PF_INET,
                                     SOCK_STREAM,  /* SOCK_STREAM for TCP. */
                                     IPPROTO_TCP );

    /* Check the socket was created. */
    configASSERT( xClientSocket != FREERTOS_INVALID_SOCKET );

    /* If FREERTOS_SO_RCVBUF or FREERTOS_SO_SNDBUF are to be used with
    FreeRTOS_setsockopt() to change the buffer sizes from their default then do
    it here!.  (see the FreeRTOS_setsockopt() documentation. */

    /* If ipconfigUSE_TCP_WIN is set to 1 and FREERTOS_SO_WIN_PROPERTIES is to
    be used with FreeRTOS_setsockopt() to change the sliding window size from
    its default then do it here! (see the FreeRTOS_setsockopt()
    documentation. */

    /* Set send and receive time outs. */
    FreeRTOS_setsockopt( xClientSocket,
                         0,
                         FREERTOS_SO_RCVTIMEO,
                         &xTimeOut,
                         sizeof( xTimeOut ) );

    FreeRTOS_setsockopt( xClientSocket,
                         0,
                         FREERTOS_SO_SNDTIMEO,
                         &xTimeOut,
                         sizeof( xTimeOut ) );

    /* Bind the socket, but pass in NULL to let FreeRTOS+TCP choose the port number.
    See the next source code snipped for an example of how to bind to a specific
    port number. */
    FreeRTOS_bind( xClientSocket, NULL, xSize );
}

Creating, configuring and binding a TCP client socket


void vCreateTCPServerSocket( void )
{
struct freertos_sockaddr xClient, xBindAddress;
Socket_t xListeningSocket, xConnectedSocket;
socklen_t xSize = sizeof( xClient );
static const TickType_t xReceiveTimeOut = portMAX_DELAY;
const BaseType_t xBacklog = 20;

    /* Attempt to open the socket. */
    xListeningSocket = FreeRTOS_socket( PF_INET,
                                        SOCK_STREAM,  /* SOCK_STREAM for TCP. */
                                        IPPROTO_TCP );

    /* Check the socket was created. */
    configASSERT( xListeningSocket != FREERTOS_INVALID_SOCKET );

    /* If FREERTOS_SO_RCVBUF or FREERTOS_SO_SNDBUF are to be used with
    FreeRTOS_setsockopt() to change the buffer sizes from their default then do
    it here!.  (see the FreeRTOS_setsockopt() documentation. */

    /* If ipconfigUSE_TCP_WIN is set to 1 and FREERTOS_SO_WIN_PROPERTIES is to
    be used with FreeRTOS_setsockopt() to change the sliding window size from
    its default then do it here! (see the FreeRTOS_setsockopt()
    documentation. */

    /* Set a time out so accept() will just wait for a connection. */
    FreeRTOS_setsockopt( xListeningSocket,
                         0,
                         FREERTOS_SO_RCVTIMEO,
                         &xReceiveTimeOut,
                         sizeof( xReceiveTimeOut ) );

    /* Set the listening port to 10000. */
    xBindAddress.sin_port = ( uint16_t ) 10000;
    xBindAddress.sin_port = FreeRTOS_htons( xBindAddress.sin_port );

    /* Bind the socket to the port that the client RTOS task will send to. */
    FreeRTOS_bind( xListeningSocket, &xBindAddress, sizeof( xBindAddress ) );

    /* Set the socket into a listening state so it can accept connections.
    The maximum number of simultaneous connections is limited to 20. */
    FreeRTOS_listen( xListeningSocket, xBacklog );

    for( ;; )
    {
        /* Wait for incoming connections. */
        xConnectedSocket = FreeRTOS_accept( xListeningSocket, &xClient, &xSize );
        configASSERT( xConnectedSocket != FREERTOS_INVALID_SOCKET );

        /* Spawn a RTOS task to handle the connection. */
        xTaskCreate( prvServerConnectionInstance,
                     "EchoServer",
                     usUsedStackSize,
                     ( void * ) xConnectedSocket,
                     tskIDLE_PRIORITY,
                     NULL );
    }
}

Creating, configuring and binding a TCP server socket

<< Back to the RTOS TCP networking tutorial index

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Create, Configure and Bind a TCP Socket Part of the FreeRTOS+TCP Networking Tutorial

The FreeRTOS Ecosystem Showcase . . .
A Selection of Add-on and Complementary Products

Create, Configure and Bind a TCP Socket
Part of the FreeRTOS+TCP Networking Tutorial