接收 UDP 数据（零拷贝接口）
FreeRTOS-Plus-TCP 联网教程节选

static void vUDPReceivingUsingZeroCopyInterface( void *pvParameters )

{

int32_t lBytes;

uint8_t *pucUDPPayloadBuffer;

struct freertos_sockaddr xClient, xBindAddress;

uint32_t xClientLength = sizeof( xClient ), ulIPAddress;

Socket_t xListeningSocket;



   /* Attempt to open the socket. */

   xListeningSocket = FreeRTOS_socket( FREERTOS_AF_INET, 

                                          /* FREERTOS_AF_INET6 to be used for IPv6 */

                                       FREERTOS_SOCK_DGRAM, 

                                          /*FREERTOS_SOCK_DGRAM for UDP.*/

                                       FREERTOS_IPPROTO_UDP );



   /* Check the socket was created. */

   configASSERT( xListeningSocket != FREERTOS_INVALID_SOCKET );



   /* Bind to port 10000. */

   xBindAddress.sin_port = FreeRTOS_htons( 10000 );

   FreeRTOS_bind( xListeningSocket, &xBindAddress, sizeof( xBindAddress ) );



   for( ;; )

   {

       /* Receive data from the socket.  ulFlags has the zero copy bit set

          (FREERTOS_ZERO_COPY) indicating to the stack that a reference to the

          received data should be passed out to this RTOS task using the second

          parameter to the FreeRTOS_recvfrom() call.  When this is done the

          IP stack is no longer responsible for releasing the buffer, and

          the RTOS task must return the buffer to the stack when it is no longer

          needed.  By default the block time is portMAX_DELAY but it can be

          changed using FreeRTOS_setsockopt(). */

       lBytes = FreeRTOS_recvfrom( xListeningSocket,

                                   &pucUDPPayloadBuffer,

                                   0,

                                   FREERTOS_ZERO_COPY,

                                   &xClient,

                                   &xClientLength );



       if( lBytes > 0 )

       {

           /* Data was received and can be processed here. */

       }



       if( lBytes >= 0 )

       {

           /* The receive was successful so this RTOS task is now responsible for

              the buffer.  The buffer must be freed once it is no longer

              needed. */



           /*

            * The data can be processed here.

            */



           /* Return the buffer to the TCP/IP stack. */

           FreeRTOS_ReleaseUDPPayloadBuffer( pucUDPPayloadBuffer );

       }

   }

}