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Re: [lwip-users] Question about socket send

From: Kieran Mansley
Subject: Re: [lwip-users] Question about socket send
Date: Mon, 20 Jul 2009 10:53:23 +0100

On Mon, 2009-07-20 at 02:28 -0700, megatron wrote:
> Thanks kieran for your reply.
> I tried 1.3.1 rc1 these days,But I got  the same result. I  enabled LWIP
> STATS,and used wireshark to capture tcp packets. The attchement is the stats
> and packets.  IP is the PC with WINXP,IP is the
> lpc2368 runs lwip and ucos-ii. The original packets are huge,there are
> 620482 packets ,I only get NO.1 to NO.199 packets here, packet from NO.200
> to NO.620481 are repetition of [TCP zerowindow][TCP Keep-Alive],[TCP
> Keep-Alive ACK],just the same with NO.162 to NO.163,until NO.620482,the PC
> sends TCP RST.

The windows XP node has reduced the available window to < 1 MSS, and
lwIP is waiting for it to get bigger.  Windows XP never seems to make
any more available, so the connection has deadlocked.  I'm not sure who
is technically at fault here - probably both - but the solution to this
would be to make lwIP tolerate very small windows and send what data it
can.  Until now we've deliberately avoided splitting packets in the send
queue.  This won't be fixed before 1.3.1 as I think it needs more
thought.  I'm sure it's something that has been discussed before but I
don't remember the conclusion.

The stats show that you are occasionally running out of memory, so you
might like to look at the balance between different users of memory to
tune how much is available.


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