Antw: RE: [lwip-users] pbuf_header fails in etharp_output

[Matthias Weisser]

>>> "Goldschmidt Simon" <address@hidden> 
>> lwIP is a little bit cheeky and reuses the pbuf with the ICMP 
>> request to form the ICMP reply.  It is therefore assuming 
>> that there is room at the front for the necessary headers.  I 
>> suppose if your ethernet driver was being very efficient and 
>> had stripped off the ethernet header before creating the 
>> pbuf, this might not be the case.  Can you show how you're 

Yes, that's what I am doing. If a ethernet frame with type IP arrives I strip 
the 14 byte ethernet header. But not because I want to save memory (RAM is not 
the big problem in my system) but because I need the IP header aligned at a 4 
byte boundary.

> If that's the case, it should be changed so that etharp can add
> a PBUF_RAM in front. To me such a driver seems a good idea
> for low memory targets (if you don't want to pass received IP
> frames through etharp).

Can you give me a little hint on how to do this or a advise how to put the 
ethernet packets into the pbufs to prevent alignment problems.


Matthias