[lwip-users] lwip_standard_chksum()

[Christiaan Simons]

Hi all,

It seems lwip_standard_chksum() from inet.c 1.22 and up
is disfunctional for the c16x and likely other 16 bit mcu's.

As far as I understand the problem is in that the source data
(void *dataptr ... ) can be at an odd (unaligned) address.

This was "solved" by a patch posted by Peter Jolasson
a few months ago and was partially committed by Leon.
(a crude/dubious runtime test for odd addresses was removed)

IMHO we need to change our reference implementation
to be correct for any architecture.

I've got some ideas:

* Add octets (byte-by-byte) instead of 16 bit words as shown in RFC1071 p5.
This will lower the performance for >8 bit architectures (a lot),
but will be alignment independant.

* Revert to the pre 1.22 routine, and enforce compile-time alignment by
changing
the function argument "void* dataptr" into "u16_t* dataptr" _and_ ensure
that  pbuf->payload pointers (all args passed to LWIP_CHKSUM) are aligned
to u16_t.

Anyone got another (better) idea?

Christiaan Simons

Hardware Engineer
Axon Digital Design

+31 (0)13 511 66 66
+31 (0)13 511 41 51

http://www.axon.tv



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