Download FreeRTOS

Quality RTOS & Embedded Software

Simplifying Authenticated Cloud Connectivity for Any Device.
Designing an energy efficient and cloud-connected IoT solution with CoAP.
Introducing FreeRTOS Kernel version 11.0.0:
FreeRTOS Roadmap and Code Contribution process.
OPC-UA over TSN with FreeRTOS.

Receiving Data Using a TCP Socket (zero copy interface)
Part of the FreeRTOS-Plus-TCP Networking Tutorial

Refer to Receiving UDP Data (zero copy interface) for receiving data using UDP zero copy interface.

FreeRTOS_recv() is used to receive data from a TCP socket. FreeRTOS_recv() cannot be called until the TCP socket has been created, configured, bound and connected to a remote socket.

The source code below demonstrates how to use FreeRTOS_recv() to place received data into a buffer using the zero copy interface. In the example it is assumed that the socket has already been created and connected.

#define BUFFER_SIZE 512

static void prvEchoClientRxTask( void *pvParameters )
Socket_t xSocket;
static char cRxedData[ BUFFER_SIZE ];
BaseType_t lBytesReceived;

/* It is assumed the socket has already been created and connected before

being passed into this RTOS task using the RTOS task's parameter. */

xSocket = ( Socket_t ) pvParameters;

for( ;; )

uint8_t *pucZeroCopyRxBuffPtr = NULL;

/* Receive data from the socket. xFlags 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_recv() 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 using the FreeRTOS_ReleaseTCPPayloadBuffer() API. */

lBytesReceived = FreeRTOS_recv( xSocket, /* The socket being received from. */
&pucZeroCopyRxBuffPtr, /* While using FREERTOS_ZERO_COPY flag,

pvBuffer is taken as a double pointer which will

be updated with pointer to TCP RX stream buffer. */

ipconfigTCP_MSS, /* The size of the buffer provided to

receive the data. */


zero copy. */

if( pucZeroCopyRxBuffPtr != NULL )
/* Copy the data to application buffer if its required to be processed later */
memcpy( &cRxedData, pucZeroCopyRxBuffPtr, lBytesReceived );

/* Release the memory that was previously obtained by calling FreeRTOS_recv()

with the flag 'FREERTOS_ZERO_COPY' */

FreeRTOS_ReleaseTCPPayloadBuffer( xSocket, pucZeroCopyRxBuffPtr, lBytesReceived );

if( lBytesReceived > 0 )
/* Data was received, process it here. */
prvProcessData( cRxedData, lBytesReceived );
else if( lBytesReceived == 0 )
/* No data was received, but FreeRTOS_recv() did not return an error.

Timeout? */

/* Error (maybe the connected socket already shut down the socket?).

Attempt graceful shutdown. */

FreeRTOS_shutdown( xSocket, FREERTOS_SHUT_RDWR );

/* The RTOS task will get here if an error is received on a read. Ensure the

socket has shut down (indicated by FreeRTOS_recv() returning a -pdFREERTOS_ERRNO_EINVAL

error before closing the socket). */

while( FreeRTOS_recv( xSocket, pcBufferToTransmit, xTotalLengthToSend, 0 ) >= 0 )
/* Wait for shutdown to complete. If a receive block time is used then

this delay will not be necessary as FreeRTOS_recv() will place the RTOS task

into the Blocked state anyway. */

vTaskDelay( pdTICKS_TO_MS( 250 ) );

/* Note - real applications should implement a timeout here, not just

loop forever. */


/* Shutdown is complete and the socket can be safely closed. */
FreeRTOS_closesocket( xSocket );

/* Must not drop off the end of the RTOS task - delete the RTOS task. */
xTaskDelete( NULL );
Example using FreeRTOS_recv()

<< Back to the RTOS TCP networking tutorial index

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.