Re: [lwip-users] etharp_tmr(), ip_reass_tmr()...

[Simon Goldschmidt]

I certainly can *not* tell you what the Xinlinx code does, you will have to ask 
Xilinx about that, not us! However, maybe there are users reading this list who 
can help you, but I wouldn't count on that...

In general, the timer functions for ARP and IP reassembly are there to free 
memory by removing outdated entries (IP fragments of packets that never were 
completed, ARP entries not used any more, etc.). If you don't call the timer 
functions, you will sooner or later run out of memory (or the code might free 
an arbitrary entry while trying to remove the oldest: without the timer 
function, it has no way of detecting the oldest).

Thus, lwIP might run without the timer functions, but if so, you're lucky! It 
is certainly not supported to run without timer functions!

About NO_SYS: with NO_SYS=0, the timer functions are called automatically from 
tcpip_thread, with NO_SYS=1, the port has to call the *_tmr() functions on its 
own in the correct intervals.

Simon


> In our project we use lwIP to send UDP packets, and lwIP also handle
> ARP, ICMP, IP fragmentation... All example code and documentation I have
> read include a timer in the projects, but I have tested our design
> without timer, and it works fine. Do I have to include a timer in the
> project?
> 
> I have read that etharp_tmr() and ip_reass_tmr() must be called. Our
> system is working fine without, but will it crash later because we don't
> call the timer functions? Do we have to call them or do the Xilinx
> adapter functions call them? I have tried to read the source code for
> lwIP, and it seems like the timer functions are called only if NO_SYS =
> 0. Am I right? Are there other timer functions we have to call?
> 
> We use lwIP 1.3.0 on a MicroBlaze processor without OS on a Spartan 3A
> DSP 1800 FPGA.

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