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RE: [lwip-users] lwip + sam7x = udef exception


From: Kieran Mansley
Subject: RE: [lwip-users] lwip + sam7x = udef exception
Date: Wed, 14 Feb 2007 12:52:24 +0000

On Wed, 2007-02-14 at 12:23 +0000, B B wrote:
> 
> Hi again,
>  
> correction to the below, the address calculated
> is resulting in a 2 byte aligned value and not 4 byte as required.
>  
> (struct tcp_hdr *)((u8_t *)p->payload + IPH_HL(iphdr) * 4) =
> 0x0020b1fa

This suggests that p->payload is also not 4-byte aligned (as "+ IPH_HL
(iphdr) * 4" should not change the bottom 2 bits), which in turn
suggests that when the data was put into the pbuf, it wasn't done in a
way that guarantees the headers and payloads will fall on the required
alignment.  For example, with ethernet which has 14 byte headers, a
driver will normally arrange to put the ethernet header on at a 2 byte
offset, so that the IP header, TCP header and packet data all align on 4
byte boundaries.

How are you creating and filling your packet buffers?

Kieran 





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