Re: [lwip-users] Delelop TCP/IP Stack for Microcontroller

[David Brown]

On 14/11/2012 11:22, Thirumalesha N wrote:
> Dear All,
>
>          I'm new to lwip TCP/IP stack, I'm trying to implement udp
> protocol for MPC5566 Microcontroller based controller card, I want
> exhibit communication between controller card and PC(Running GUI based
> application (UDP protocol implemented)).
>
>         I'm trying to develop TCP(UDP)/IP protocol for controller..how
> do I proceed...?
>
> Regards
> Thiru N

I've got lwIP working on another microcontroller of that family.  I am 
not at liberty to publish any of the low-level code for the driver, but 
I can give you some hints.  (One day it would be nice to re-write the 
code so that it could be published, but it is not easy to find the time 
for such work.)

The driver itself was heavily inspired by the Coldfire FEC example for 
lwIP.  The MPC's FEC has a lot of functionality - it can do things like 
scatter-gather DMA so that you can have the IP header and the packet 
contents in different buffers in memory, or send out the different parts 
of a lwIP pbuf chain without doing any copying and concatenation in the 
program.  However, it is also possible to ignore this - my driver code 
does the concatenation and copying so that the FEC code is as simple as 
possible.  It is less efficient, but a lot easier to get working.

One thing to watch out for is that the FEC has it's own DMA engine that 
does not snoop the processor's cache (unlike the normal eDMA engine on 
the chip).  That means you have to make sure caches are flushed around 
accesses to ram that the FEC accesses, or make sure that those memory 
areas are non-cached.

Hope that helps!

David