Re: [lwip-users] problems and solutions (?)

[Chris WIlliams]

In message , address@hidden writes
>Subject: Re: [lwip-users] problems and solutions (?)
>To: "Mailing list for lwIP users" <address@hidden>
>Message-ID: <address@hidden>
>Content-Type: text/plain;      charset="iso-8859-1"
>
>Hi Kieran,
>
>I'll follow your suggestion to inform you about problems I encountered. I'm
>working on a XC161-Board with CS8900a using GNU-C (from Hightec). I tried to
>build an easy webserver application using the minimal unix 'echo server'
>application as an example how to use the raw api.
>
>It didn't work. Not even the TCP SYN frame from the browser of my PC had
>been answered by lwip. The reason for this was that a call to pbuf_header()
>from etharp_output() failed because there was not enough space allocated for
>the pbuf to hold the link layer header.
>
>I was able to fix this by changing the definition of PBUF_LINK_HLEN (which
>was set to 0 !?) in opt.h to the actual size of 14 for the link layer
>header. Afterwards everything seemed to work quite well.
>
>Are there any applications or drivers where a definition of
>
>#define PBUF_LINK_HLEN        0
>
>makes any sense?
>
>Uwe


I have a file lwipopts.h with the definition:

/* PBUF_LINK_HLEN: the number of bytes that should be allocated for a
        link level header. */
#define PBUF_LINK_HLEN          16

This is overriding the value of 0 quoted above so my system works.

Can anyone explain why I have an override of 16 and could I change it to
14?

Thanks, Chris.
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