[lwip-users] Re: [lwip] lwIP 0.5.3 tcp Checksum issues?

[Jani Monoses]

x86 can address individual bytes so there is no specific requierement
as far as correctness is concerned.

> What *is* the correct alignment for a Linux test application running on
> i686?
> 
> Dirk
> 
> On Mon, 2002-07-22 at 13:09, Jani Monoses wrote:
> > Hi
> > as Florian said it could be an alignment issue.
> > I had bad checksums because the data in httpd was not 4byte aligned.
> > In the file where those binary structs live (fsdata.c) make the structs 
> > aligned with the gcc attribute feature.I used an ARM processor.
> > Jani.
> > 
> > > Hi all.
> > > 
> > >   Are there any known issues with 0.5.3 with regards to checksum 
> > > calculation?
> > > 
> > >   Specifically, I am testing my own httpd server (heavily modified from 
> > > the original using the raw api) and pages don't get displayed. I am 
> > > tracking this down to the fact that the responding packet of data is 
> > > sent, but packet sniffing software says it has an invalid tcp checksum 
> > > and my PC isn't ACKing. The data just keeps getting resent with the same 
> > > incorrect checksum.
> > > 
> > >   The main index web page supplied in the lwIP archive works ok, others 
> > > don't, so it seems to depend on the data content.
> > > 
> > >   What's strange is I had tested this code and it works under the win32 
> > > port (and still does work) - although due to different timings the exact 
> > > sequence of events are different.
> > > 
> > >   What's even more annoying is that I have compared the ROM pbuf checksum 
> > > total with the win32 port's ROM pbuf checksum total - they are equal. I 
> > > have calculated manually the TCP pbuf checksum and added this all up with 
> > > the pseudo header and get the same checksum as that which was sent with 
> > > the packet !! Surely the packet sniffing software and windows 2000 
> > > checksum implementation is correct ? ! I can assume that can't I ? ! :-)
> > > 
> > > Regards,
> > > Michael Portmann
> > > 
> > > HYDRA Electronic Design Solutions Pty Ltd
> > > 140 Ashley Street, Underdale, SA 5032.
> > > Ph. +61 8 8234-0477
> > > Fx. +61 8 8234-1840
> > > 
> > > [This message was sent through the lwip discussion list.]
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> 
> 
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