I'm using FreeRTOSrecvfrom with the FREERTOSZERO_COPY flag.

Please confirm that the message received via this call is directly from the network buffer with no mid-stream coping.

Also, I am expecting a "group" of these messages being received back-to-back with little time between them. Since the stack is running at a hight priority than my task calling FreeRTOSrecvfrom, will the stack drop or "queue" another incoming message if I have not finished initial processing of the previous message and gotten back to issue another FreeRTOSrecvfrom call?

Thanks.

Joe

Please confirm that the message received via this call is directly from the network buffer with no mid-stream coping.

Assuming your network driver does not itself copy the data - then yes - at least for UDP, its more complicated for TCP.

Also, I am expecting a "group" of these messages being received back-to-back with little time between them. Since the stack is running at a hight priority than my task calling FreeRTOSrecvfrom, will the stack drop or "queue" another incoming message if I have not finished initial processing of the previous message and gotten back to issue another FreeRTOSrecvfrom call?

Again - assuming your driver does not drop messages - then it will queue messages until you run out of network buffers. If you run out of network buffers then it will drop packets. If dropped packets form part of a TCP stream then the TCP protocol will ensure the packets are re-transmitted.

Joe,

The name "+TCP stack" can be misleading, because it includes both +UDP ( the former version of FreeRTOS' IP-stack ) and +TCP.

A UDP packet travels on its own from end-point to end-point. And as +TCP doesn't implement Ethernet fragmentation, there will be single Ethernet message per UDP packet ( Fragmentation would make it possible to transmit larger datagrams ).

Only TCP sockets have a stream buffer.

UDP sockets are much simpler. A UDP socket puts the received Network Buffers into a List. As Richard wrote, UDP packets can travel zero-copy, all the way from DMA-reception in the EMAC until the user application.

In FreeRTOS_DHCP.c you find an example of zero-copy reception:

uint8_t *pucUDPPayload;
int32_t lBytes;

lBytes = FreeRTOS_recvfrom( xDHCPData.xDHCPSocket, ( void * ) &pucUDPPayload,
    0ul, FREERTOS_ZERO_COPY, &xClient, &xClientLength );
if( lBytes > 0 )
{
    /* Use the 'lBytes' UDP payload data. */
    FreeRTOS_ReleaseUDPPayloadBuffer( ( void * ) pucUDPPayload );
}

Note that pucUDPPayload is a bit of a special pointer. It points somewhere halfway in the pucEthernetBuffer of a NetworkBufferDescriptor_t. The Ethernet Header, the IP-header and UDP-header are skipped. pucUDPPayload points to the first data-byte of the UDP-payload.

FreeRTOS_ReleaseUDPPayloadBuffer() will find the pucEthernetBuffer and it will release the original NetworkBufferDescriptor_t.

Does that make sense?

I think that the FREERTOS_ZERO_COPY flag is exactly what you are looking for.

I am expecting a "group" of these messages being received back-to-back with little time between them.

Normally when you receive N packets, the network driver will queue N messages for the IP-task. When packets are received in a burst, the driver can link them together in a chain and put a single message into the queue. You can reach quite a performance gain with this technique:

#define ipconfigUSE_LINKED_RX_MESSAGES    1

Find an example at the bottom of this post.

Since the stack is running at a higher priority than my task calling FreeRTOSrecvfrom, will the stack drop or "queue" another incoming message if I have not finished initial processing of the previous message and gotten back to issue another FreeRTOSrecvfrom call?

As Richard wrote: the driver will queue-up packets as long as there are Network Buffers available.

Example of using linked RX messages:

~~~~

void linked_rx_receive()
{
NetworkBufferDescriptor_t *pxHead = NULL;
NetworkBufferDescriptor_t *pxTail = NULL;

    for( ;; )
    {
        /* driver_receive() returns the next available packet.
        It may not block. When nothing has arrived, it returns
        NULL. */

        pxNetworkBuffer = driver_receive();

        if( pxNetworkBuffer == NULL )
        {
            /* That's it for now. */
            break;
        }
        if( pxHead == NULL )
        {
            /* Remember the first packet. */
            pxHead = pxNetworkBuffer;
        }
        if( pxTail != NULL )
        {
            /* Make the link */
            pxTail->pxNextBuffer = pxNetworkBuffer;
        }
        /* Remember the last packet. */
        pxTail = pxNetworkBuffer;
    }
    if( pxHead != NULL )
    {
        IPStackEvent_t xRxEvent;

        /* Just make sure that the last item has no next buffer: */
        pxTail->pxNextBuffer = NULL;

        xRxEvent.eEventType = eNetworkRxEvent;
        xRxEvent.pvData = ( void * )pxHead;

        /* Send a linked list of packets. */
        if( xSendEventStructToIPTask( &xRxEvent, ( portTickType ) 1000 ) != pdPASS )
        {
            /* Sending failed, make sure to release every linked Network Buffer! */
        }
    }
}

~~~~