FreeRTOS_select()

[FreeRTOS-Plus-TCP API Reference]

FreeRTOS_sockets.h

BaseType_t FreeRTOS_select( SocketSet_t xSocketSet, TickType_t xBlockTimeTicks );

Block on a "socket set" until an event of interest occurs on a socket within the set. ipconfigSUPPORT_SELECT_FUNCTION must be set to 1 in FreeRTOSIPConfig.h for FreeRTOS_select() (and its associated functions) to be available.

Socket Sets allow an application RTOS task to block on multiple sockets simultaneously.

To use a socket set:

Create a socket set by calling FreeRTOS_CreateSocketSet(). A socket set is equivalent to the Berkeley sockets fd_set type.
Add one or more sockets to the set using calls to FreeRTOS_FD_SET(). FreeRTOS_FD_SET() is equivalent to the Berkeley sockets FD_SET() macro.
Call FreeRTOS_Select() to test the sockets in the set to see if any of the sockets have an event pending.
If FreeRTOS_select() returns a non-zero value then check all sockets in the set using a call to FreeRTOS_FD_ISSET() to determine which events are pending.

A socket can only be a member of one set at any time.

The FreeRTOS_FD_CLR() API function removes a socket from a set.

Parameters:

xSocketSet	The socket set being tested.
xBlockTimeTicks	The maximum time, in ticks, that the calling RTOS task will remain in the Blocked state (with other tasks executing) to wait for a member of the socket set to get an event.

Returns:

If xBlockTimeTicks expired before a socket in the socket set had an event, then zero is returned. Otherwise a non-zero value is returned. All sockets which belong to the socket set must be checked by calling FreeRTOS_FD_ISSET()

If a socket in the set receives a signal, causing the task that was blocked on the socket to abort its read operation, then the call to FreeRTOS_select() will return eSELECT_INTR.

Example usage:



/* FreeRTOS includes. */

#include "FreeRTOS.h"

#include "task.h"

#include "queue.h"



/* FreeRTOS-Plus-TCP includes. */

#include "FreeRTOS_IP.h"

#include "FreeRTOS_Sockets.h"



static void prvMultipleSocketRxTask( void *pvParameters )

{

SocketSet_t xFD_Set;

BaseType_t xResult;

Socket_t xSockets[2];

struct freertos_sockaddr xAddress;

uint32_t xClientLength = sizeof( struct freertos_sockaddr ), x;

uint32_t ulReceivedValue = 0;

int32_t lBytes;

const TickType_t xRxBlockTime = 0;



    /* Create the set of sockets that will be passed into FreeRTOS_select(). */

    xFD_Set = FreeRTOS_CreateSocketSet();



    /* Create two sockets to add to the set. */

    for( x = 0; x < 2; x++ )

    {

        /* Create the socket. */

        xSockets[x] = FreeRTOS_socket( FREERTOS_AF_INET,

                                   FREERTOS_SOCK_DGRAM,

                                   FREERTOS_IPPROTO_UDP );



        /* Bind the socket to a port number 1000, 1001... */

        xAddress.sin_port = FreeRTOS_htons( 1000 + x );

        FreeRTOS_bind( xSockets[x], &xAddress, sizeof( struct freertos_sockaddr ) );



        /* Once it has been tested that a socket has a eSELECT_READ

        event, blocking on a read call is not necessary any more.  Set the

        Rx block time to 0. */

        FreeRTOS_setsockopt( xSockets[x], 0, FREERTOS_SO_RCVTIMEO,

                             &xRxBlockTime, sizeof( xRxBlockTime ) );



        /* Add the created socket to the set for the READ event only. */

        FreeRTOS_FD_SET( xSockets[x], xFD_Set, eSELECT_READ );

    }



    for( ;; )

    {

        /* Wait for any event within the socket set. */

        xResult = FreeRTOS_select( xFD_Set, portMAX_DELAY );

        if( xResult != 0 )

        {

            /* The return value should never be zero because FreeRTOS_select() was called

            with an indefinite delay (assuming INCLUDE_vTaskSuspend is set to 1).

            Now check each socket which belongs to the set if it had an event */



            for( x = 0; x < 2; x++ )

            {

                if( FreeRTOS_FD_ISSET ( xSockets[x], xFD_Set ) )

                {

                    /* Read from the socket. */

                    lBytes = FreeRTOS_recvfrom( xSockets[x], &( ulReceivedValue ),

                                        sizeof( uint32_t ), 0, &xAddress,

                                        &xClientLength );

                    /* Process the received data here. */

                }

            }

        }

    }

}



Example use of the FreeRTOS_select() API function

Quality RTOS & Embedded Software Download FreeRTOS Menu

FreeRTOS_select() [FreeRTOS-Plus-TCP API Reference]

Quality RTOS & Embedded Software

Download FreeRTOS
Menu

FreeRTOS_select()

[FreeRTOS-Plus-TCP API Reference]