Re: [lwip-users] Understanding retransmission

[Jan Menzel]

On 19.01.2015 17:31, Simon Goldschmidt wrote:
> "Jan Menzel" wrote:
>> Your patch is already part of my code. I just disabled
>> LWIP_CHECKSUM_ON_COPY and have not seen a bad packet since then.
> 
> Great to hear that! Although LWIP_CHECKSUM_ON_COPY is not enabled by default, 
> are you in a position to debug this?
> 
> This should trigger the point where it fails:
> #define LWIP_CHECKSUM_ON_COPY          1
> #define TCP_CHECKSUM_ON_COPY_SANITY_CHECK 1
> #define TCP_CHECKSUM_ON_COPY_SANITY_CHECK_FAIL(msg) 
> LWIP_ASSERT("TCP_CHECKSUM_ON_COPY_SANITY_CHECK_FAIL", 0)
> 
> And you could then see what was enqueued by setting this:
> #define TCP_OUTPUT_DEBUG  (LWIP_DBG_ON | LWIP_DBG_TRACE)
> #define LWIP_DBG_TYPES_ON         (LWIP_DBG_ON|LWIP_DBG_TRACE)
> 
> That would be great!
> 
I've tried my very best, but I'm not sure if I captured what you need.
Please find some Wireshark frames together with corresponding log output
and lwip options file. I also captured lwip statistics in case thats of
any relevance. Maybe I did not enabled all options as I have not seen
the ASSERT() message.
        I'm not sure thats exactly going on. It seems that under very special
conditions, the checksum of outgoing TCP packets gets corrupted and is
also used for all retransmission.
        If you need anything else, please let me know. In the mean while I'll
try to force all outgoing checksums to be recomputed to get my project
back online.

        Jan

TCP checksum.zip
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