FreeRTOS_select()

[FreeRTOS-Plus-TCP API 引用]

FreeRTOS_sockets.h

BaseType_t FreeRTOS_select( SocketSet_t xSocketSet, TickType_t xBlockTimeTicks );

阻塞“套接字集”，直到集内的套接字上发生相关事件。必须在 FreeRTOSIPConfig.h 中将 ipconfigSUPPORT_SELECT_FUNCTION 设置为 1， FreeRTOS_select()（及其相关函数）才可用。

套接字集允许应用程序 RTOS 任务在多个套接字上同时多个套接字。

要使用套接字集，请执行下列操作：

调用 FreeRTOS_CreateSocketSet() 创建套接字集。套接字集相当于 Berkeley 套接字 fd_set 类型。
调用 FreeRTOS_FD_SET() 向套接字集添加一个或多个套接字。 FreeRTOS_FD_SET() 相当于 Berkeley 套接字 FD_SET() 宏。
调用 FreeRTOS_Select() 以测试套接字集中的套接字，查看是否有任何套接字存在挂起事件。
如果 FreeRTOS_select() 返回非零值，则调用 FreeRTOS_FD_ISSET() 检查套接字集中的所有套接字，以确定哪些事件处于挂起状态。

在任何时候，套接字都只能属于一个套接字集。

FreeRTOS_FD_CLR() API 函数可删除套接字集中的套接字。

参数：

xSocketSet	当前正在测试的套接字集。
xBlockTimeTicks	调用 RTOS 任务将保持在阻塞状态（同时执行其他任务）的最大时间（以 tick 为单位），以等待套接字集成员获取事件。

返回：

如果 xBlockTimeTicks 在套接字集中的套接字发生事件之前过期，则返回零，否则返回一个非零值。所有套接字集中的套接字必须通过调用 FreeRTOS_FD_ISSET() 进行检查。

如果套接字集中的套接字接收到信号，导致套接字上阻塞的任务中止读取操作，则对 FreeRTOS_select() 的调用将返回 eSELECT_INTR。

用法示例：



/* 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_INET4,

                                   /* FREERTOS_AF_INET6 can be used for IPv6 TCP socket */

                                   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

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

出色的 RTOS & 嵌入式软件

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FreeRTOS_select()

[FreeRTOS-Plus-TCP API 引用]