[lwip-users] Ang: Re: Ang: Re: Bare Metal / Memory Alignment
From:
ake . forslund
Subject:
[lwip-users] Ang: Re: Ang: Re: Bare Metal / Memory Alignment
Date:
Wed, 7 Sep 2011 22:54:15 +0200
I seems like I've misinterpreted something once again =) Now that I look for it I see that an array of u8_t's are inserted in the eth_header struct.
My compiler hints for structure packing should however be functional for the compiler shipped with Keil uVision 3.x (and probably for the 4.x aswell) as long as there are no partially packed structs...
/Åke ----------------------------- Åke Forslund 0433-273296 NIBE AB Box 14 S-285 21 Markaryd Tel +46-(0)433-273296
address@hidden skrev: -----
Till: Mailing list for lwIP users <address@hidden> Från: Simon Goldschmidt Sänt av: address@hidden Datum: 2011-09-07 22:31 Ärende: Re: [lwip-users] Ang: Re: Bare Metal / Memory Alignment
Kieran Mansley <address@hidden> wrote:
> > On 7 Sep 2011, at 16:59, address@hidden wrote: > >> I recently got the impression that structure-packing wasn't mandatory and could be replaced with padding, I'm not at all sure about this > > I think structure packing is the only sensible way of ensuring you get correct behaviour.
> Most protocol headers happen to be aligned correctly for 32-bit processors if you insert 2 bytes before the Ethernet header. However, that's not supported by us, currently. So if it works, it does so by chance... If you get it to work without packing, you're lucky enough, but I doubt that it has too big of an influence on throughput, as many header members are only read once.