Re: [lwip-users] STM32F4+lwIP: TCP MSS sets to 536 bytes on its own

[Jagdish Panchal]

Hi,

First of all thanks for responding.

Want to inform that the problem is solved. The issue was in the firmware build.  

As of now the problem is solved, but curious to know why the PC was dividing the packets because of this. OS is Windows 10. 

​regards,

Jagdish​

On Sat, Jun 23, 2018 at 9:30 PM, <address@hidden> wrote:

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Today's Topics:

   1. Re: STM32F4+lwIP: TCP MSS sets to 536 bytes on its own
      (address@hidden)
   2. lwIP Packets are not received (M S ARUL)


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Message: 1
Date: Fri, 22 Jun 2018 20:26:56 +0200
From: "address@hidden" <address@hidden>
To: Mailing list for lwIP users <address@hidden>
Subject: Re: [lwip-users] STM32F4+lwIP: TCP MSS sets to 536 bytes on
        its own
Message-ID: <d86190b3-f6d9-e0da-ab23-address@hidden>
Content-Type: text/plain; charset=utf-8; format=flowed

On 21.06.2018 17:52, Jagdish wrote:
> Hi,
> Am using lwIP stack with STM32F4 series micro-controller in one of project
> board. Trying to connect this board to pc based application. I observed,
> When host sends packet of size 1088 bytes, the packet gets divided into 2.
> Please refer the packet where length column shows 590 and 552.

If you want a packet trace to be analyzed, send a packet trace, not a
picture. In the case of a tcp transfer, be sure to include the start of
the connection and describe as much what you think you are seeing (e.g.
OS to IP etc.).

> In lwiopts.h, i have set TCP_MSS to 1460. Also the initial TCP handshake
> shows the MSS is 1460 from both PC and stm32f4 board.
> My understanding is that if in initial handshake the MSS is 1460. Host must
> not divide the packet in 2 segments restricting the length of packet to 536
> bytes.

No, "must not" is wrong here. A remote host can send at any small size
it wants. Note the "M" in MSS, which stands for "maximum". There's no
minimum defined.

> Kindly help me to understand and set this right. Is there a configuration in
> lwIP or on PC side that i am missing?

You could start by telling us which side is sending smaller segments, is
it lwIP or the PC? Which OS is the PC running?


Simon



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Message: 2
Date: Sat, 23 Jun 2018 17:25:27 +0530
From: M S ARUL <address@hidden>
To: Mailing list for lwIP users <address@hidden>
Subject: [lwip-users] lwIP Packets are not received
Message-ID:
        <CALokJnogMKkJycauZsP4Og7K+xYiUsuRaAeDT4qx26ok5GnNFQ@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hello All,
I`m using sama5d3xek development board. I have integrated lwIP with embOS.
It was working fine when D-Cache & I-Cache weren`t enabled. But no packets
are received after enabling the Cache Unit. Also in IAR if I select
SAMA5D35 as a device in options tab, no bytes are received. I had to select
the device as None, then only stack was working. Can someone help me find
the issue? Thanks in Advance.

Best Regards,
ARUL PRAKASH M
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