Re: [lwip-users] LLDP Implementation for lwIP

[Amit Ashara]

Hello Sergio

LLDP is a multicast information only packet. It has the be sent at fixed time 
intervals. The second approach to have a separate driver and calling it in a 
timer function seems to be the approach. Again the receive packet is easy to 
process. The transmit needs to be thought and inserted . Let me run some 
experiments and run into issues rather than sending emails on phantom issues.

Regards
Amit Ashara

On Aug 4, 2016, at 9:31 AM, Sergio R. Caprile <address@hidden> wrote:

>> psNetif->linkoutput = tivaif_transmit;
> 
>> If i check the tivaif_transmit function, "tivaif_transmit(struct
>> netif *psNetif, struct pbuf *p)" it maps the pbuf to the MAC
>> controller for transmission. It is this buffer that needs to be
>> modified for LLDP frame.
> 
> Not exactly. You need to allocate a pbuf, fill it with your data, give
> it to tivaif_transmit(), and free it when it is done. Unless there is
> some retransmission mechanism inside LLDP (which I don't know), then it
> is done when the controller has it in its memory. Unless it is a
> zero-copy driver (looks so, DMA perhaps?), in which "the controller
> memory and the pbuf memory is the same space", so you need to know when
> it has been transmitted to free it. I have no expertise in this area,
> but there is this:
> http://lwip.wikia.com/wiki/Writing_a_device_driver#Notes_on_Zero-Copy_Network_interface_drivers
> 
>> However the call stack is always from TCP or DHCP (even when ARP is
>> called which is a link layer packet).
> 
> That is because you said you just needed the output phase ;^)
> The stack is answering because it is receiving the datagrams.
> Now you need to check your input to see why. You can go two paths, and I
> suggest you take both, not necessarily in this order.
> 
> (1) Go back to my first mail, where I've shown you code that explains this
> 
> (2) Read this:
>    http://lwip.wikia.com/wiki/Writing_a_device_driver
> 
> ARP is link layer but is part of the IP suite, so the stack supports ARP
> and the link level driver has been configured to deliver ARP to lwIP
> input function.
> 
> 
> 
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