[lwip-devel] ARM7 data abort exception - hacky solution

[John Martindale]

Hi all,

 

Just thought I'd post here in case this information helps anyone else.

 

I've been trying to port lwIP 1.3.0 to an ARM7 platform (LPC2148) running TNKernel 2.5 as the OS and interfacing a DM9000 device. When I ran the port I would keep getting data abort asserts, caused by trying to read invalid memory locations (for a great description of how to trap and diagnose these errors, see http://www.embedded.com/192202641). This was especially apparent with DHCP enabled (crashed immediately).

 

After a period of (slightly random!) tinkering with the code I found that the problem (or maybe just *a* problem?) is due to the pointers used in memory management (I’m using the default memory scheme). In mem.h, if the memory pool is <64000 bytes, then uint16 pointers are used. By forcing these to be uint32 pointers everything starts working. Altered code:

//if MEM_SIZE > 64000l

#if 1

typedef u32_t mem_size_t;

#else

typedef u16_t mem_size_t;

#endif /* MEM_SIZE > 64000 */

 

Relevant lwipopts.h settings:

#define MEM_ALIGNMENT           4

#define ETH_PAD_SIZE                    2

 

So now I have the lwIP stack running smoothly, pinging, telnet server, (basic) http server, lovely! I haven’t had time to analyse exactly what is going on or why this works, but it might be related to this: http://lists.nongnu.org/archive/html/lwip-devel/2008-01/msg00181.html? It also doesn’t seem like a clean solution – so if anyone has a better fix please post it up.

 

Anyway, hope this helps someone else,

John Martindale

 

Practical Control Ltd

448 Brightside Lane

Sheffield

S9 2SP

T: 0114 2561888

F: 0114 2617052

www.practicalcontrol.com