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Fwd: [lwip-users] netconn api problem

From: Tyrel Newton
Subject: Fwd: [lwip-users] netconn api problem
Date: Wed, 24 Nov 2010 07:08:42 -0800

Resubmitting this question as I didn't get any feedback the first time around.

> I have an 10Mbit Ethernet application that strictly uses TCP via the netconn 
> API. All TCP writes are done with the NETCONN_COPY flag. I have 128MB of RAM 
> in my system and all of the resource sizes set pretty high in lwipopts.h. I 
> monitor the resources and I have yet to see the max come close to the avail.
> A problem occurs when I do the following:
> 1) send a huge buffer via a single call to netconn_write with sizes well over 
> 64kB (usually in the 0.25~1 MB range)
> 2) immediately send a pretty small buffer (much less than the MSS for 
> Ethernet) via a single call to netconn_write
> The problem is that the first byte (and only the first byte) of the second 
> netconn_write call seems to get dropped. This happens randomly and not 
> terribly frequently (maybe 10% of the time at worst). I can mitigate the 
> problem by inserting a few seconds of delay between the two calls to 
> netconn_write. The delay, I think, gives lwIP plenty of time to empty the 
> send buffer and process the numerous TCP ACKS that are required to send the 
> large buffer of data. The longer the delay, the less likely the first byte of 
> the second call gets dropped.
> I'm connecting to lwIP from a Windows PC via a socket in python. I have a 
> hard time believing the PC is dropping the byte. I know I could verify this 
> with Wireshark, but since the problem is random and not too frequent, it 
> would take me forever to wade through the lengthy packet history.
> Anybody have any insight and/or guidance on where I might go in the code or 
> what settings I might tweak to fix and/or understand this issue?
> Other lwipopts.h settings that might be relevant:


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