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RE: [lwip-devel] Help with TCP stream errors.

From: Bill Auerbach
Subject: RE: [lwip-devel] Help with TCP stream errors.
Date: Thu, 30 Apr 2009 17:35:02 -0400

>Sounds like the hardware might be generating the wrong checksum.  If it
>did this consistently, the connection would never be able to recover, as
>the sequence would go something like this:

Wow, Kieran, I'm impressed.  You are in fact correct.  Although we had 
thoroughly tested the hardware implementation, there was a small race condition 
in handling carry-outs and very intermittently we were missing the ending carry 
and were off by 1.  In a tight loop comparing hardware and software methods 
with random data and data sizes and alignment for thousands of passes, it never 
failed.  Only in the full application sending and receiving data "live" would 
it do this.

After you posted this, I tested the 2 methods while running live and did catch 
hardware checksums that didn't match the software checksum. I did this check a 
lot sooner than I would have had it not been for your help.  Thank you!!!


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