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Altera_Forum
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21 years ago

Checksum Error LWIP

I am seeing checksum errors when using the cyclone development board (192.168.100.5) connected to a hub connected to my PC (192.168.100.5).

The error seems to add a 1 sec delay before it moves on. The delay is to much for my application.

Any idea how to address the issue or shorten the delay after checksum error is found?

I am using IDE Version: 1.1.0 Build: 137.

Here is the trace of the packets around the 1 sec delay using Ethereal. The communication is using TCP.

No. Time Source Destination Protocol Info

29475 33.995761 192.168.100.7 192.168.100.5 TCP [TCP Dup ACK 29474#1] 2662 > 4097 [ACK] Seq=1 Ack=20109313 Win=64240 Len=0

No. Time Source Destination Protocol Info

29476 33.996663 192.168.100.5 192.168.100.7 TCP [TCP Out-Of-Order] 4097 > 2662 [PSH, ACK] Seq=20108725 Ack=1 Win=2048 [CHECKSUM INCORRECT] Len=1460

No. Time Source Destination Protocol Info

29477 33.997276 192.168.100.5 192.168.100.7 TCP [TCP Previous segment lost] 4097 > 2662 [PSH, ACK] Seq=20110773 Ack=1 Win=2048 Len=588

No. Time Source Destination Protocol Info

29478 33.997300 192.168.100.7 192.168.100.5 TCP [TCP Dup ACK 29474#2] 2662 > 4097 [ACK] Seq=1 Ack=20109313 Win=64240 Len=0

No. Time Source Destination Protocol Info

29479 35.257149 192.168.100.5 192.168.100.7 TCP [TCP Retransmission] 4097 > 2662 [ACK] Seq=20109313 Ack=1 Win=2048 Len=1460

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    21 years ago

    <div class='quotetop'>QUOTE </div>

    --- Quote Start ---

    The error seems to add a 1 sec delay before it moves on. The delay is to much for my application.

    Any idea how to address the issue or shorten the delay after checksum error is found?[/b]

    --- Quote End ---

    To be honest you need to look at the cause of the checksum errors, or provide a simple test case to reproduce it. If you really want to change the retransmission frequency, which I think will only move your problem the the function you need to look at is tcp_slowtmr in tcp.c.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    21 years ago

    Which checksum is Ethereal detecting as wrong - The &#39;frame&#39; checksum, or the TCP checksum ?

    There was a known bug in the ethernet driver with bad TCP checksums on odd length packets which I reported on this forum a couple of months back - Search for "Checksum" - The thread was called something like "lanc911.c bug - and a fix".

    - Roddy