FreeRTOS lwip/+TCP/+UDP

pugglewuggle wrote on Thursday, December 18, 2014:


Do the IP stacks for FreeRTOS only work on MCUs with built-in ethernet peripherals, or can it be set up to work with the UART? We use a cellular modem and it requires tunneling anything to be sent through its socket with AT commands. Please advise.


heinbali01 wrote on Friday, December 19, 2014:


FreeRTOS+TCP can also be used with external Ethernet peripherals. But it does not know the SLIP protocol, yet. It expects raw Ethernet IP-packets as input and it will also reply with Ethernet IP-packets.


pugglewuggle wrote on Saturday, December 20, 2014:

When you say ethernet IP packets - do you mean that it requires IP packets encapsulated with the ethernet protocol or are you just saying it requires raw IP? Do you have any examples of this?

heinbali01 wrote on Sunday, December 21, 2014:

With IP packets I mean a packet that would normally be sent on a LAN.

It has these fields:

  The Ethernet header:
    uint8_t destination_addr[6]
    uint8_t source_addr[6]
    uint16_t frame_type;

  IP- or ARP-header


Your platform will need to provide two things: a send routine and it must forward received packets to the IP-task:

/* A function which will forward / send the message to the NIC. */
portBASE_TYPE xNetworkInterfaceOutput(
    xNetworkBufferDescriptor_t * const pxMessage,
    portBASE_TYPE bReleaseAfterSend )
    /* Encapsulate and send a message. */
        pxMessage->xDataLength );

/* Forward received packets to the IP-task. */
static void vPassMessage( xNetworkBufferDescriptor_t *pxMessage )
xIPStackEvent_t xRxEvent;

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

    if( xSendEventStructToIPTask( &xRxEvent, 1000ul ) != pdPASS )
        /* Could not deliver the message, release it now. */
        vReleaseNetworkBufferAndDescriptor( pxMessage );

/* A tasking polling the input from the modem. */
void vEthernetTask( void pvParameter )
    for( ; ; )
    xNetworkBufferDescriptor_t *pxMessage;

        /* Wait for a new message from the NIC. */
        pxMessage = pxWaitForMessage( 1000 );
        if( pxMessage != NULL )
            vPassMessage( pxMessage );


I hope that the pseudo code above make a little clear what is expected of your NIC interface.


heinbali01 wrote on Saturday, December 27, 2014:


Just wondering, was the above answer enough to get on with it?

If not, maybe you can describe the kind of hardware setup that you are using, along with the library?


pugglewuggle wrote on Monday, January 05, 2015:

Very interesting. I’m not quite ready to do this right now so I’ll have to explore it more when it is time. Thanks for the answers!