Hi Timmy,
It did cross my mind but unfortunately I could only set single value as the FEC
buffer size (unless I am misinformed by the user guide).
Greetings,
Ikhwan
Date: Sun, 25 May 2008 17:47:36 +0200From: [EMAIL PROTECTED]: [EMAIL
PROTECTED]: Re: [lwip-users] Misalignment problems on PowerPC (little endian
mode)
If your FEC does not allow storing of packets at an 2 byte offset, then you
could try setting up the FEC to store the Ethernet header in one small PBUF,
and the rest of the packet in a large 1500 byte PBUF. That way your IP headers
will be aligned.The downside is of course that for this to work all incomming
packets regardless of size will use the full 1500 bytes.You would need to setup
every other pbuf in the FEC Rx DMA chain to 14 bytes and 1500 bytes
respectively.Regards,Timmy BrolinMuhamad Ikhwan Ismail wrote:
Hi Timmy, If you read my prev post, you would know why the padding is useless
to me. To Simon, Understandable. Well if someone has the same problem, and
checks this thread I guess he can always just bring it back up.PowerPC is more
robust in big endian mode, it even corrects the misalignment in big endian mode
internallly (hardware). Why and howto be honest I dont know (barely had any
training on PowerPC, learned all through books.)There are certain PowerPC
assembler intructions that cause problems in little endian mode, I dont
remember them by hard, needto check the book. Though you are correct about my
method of correcting the problem would make lwip slower : 1. My driver didnt
have to copy the received buffer at all. So I spare a lot there.2. Fixing
alignment in little endian mode is a very2 long process/routine.3. And I dont
have to copy the header everytime. E.g in TCP I only had to copy the header
once for the multiple header processing. So I hope this brings the end to the
thread, at least till someone might need something out of it. I am thankful
that so many peoplehad tried to help. Greetings,Ikhwan
> Date: Sat, 24 May 2008 22:28:38 +0200> From: [EMAIL PROTECTED]> To:
> [email protected]> Subject: Re: [lwip-users] Misalignment problems on
> PowerPC (little endian mode)> > > >> I have the source which can be compiled
> if the option > >> LWIP_MISALIGNMENT is set to 1. If anyone interested and
> have the same > >> problem, I am more than willing to share and help. If you
> guys want > >> to incorporate it to lwip as alternative solution to structure
> > >> packing I am glad I can help. This lowers the stack performance a bit >
> >> though.> >> >> > Not to offend you, but personally, I see this as a bug in
> the compiler > > you are using and we don't support broken compilers:
> structure packing > > _is_ a must for lwIP!> >> > Hope you are still having
> fun with lwIP!> >> > Simon> >> Actually, no. Structure packing is not
> necessarily a must for lwip.> In many cases lwip should work just fine
> without structure packing. I > know that Texas Instruments DSP compilers will
> work with lwip without > structure packing.> Patches made to lwip several
> years ago ensured that if ETH_PAD_SIZE is > set to 2, then no variable will
> ever be unaligned. This solves most of > the problems which would otherwise
> require structure packing.> > There are two things a compiler may do which
> will still mess up the lwip > structs:> 1: Some compilers pad the size of all
> structs so that the size of a > struct becomes a multiple of 4.> 2: Some
> comiplers put all structs on an address boundary of 4, > regardless of the
> actual boundary requirements of the members of the struct.> Compilers which
> does any of the above would still require packed > structs. Compilers which
> does neither of the above should work without > packed structs, if
> ETH_PAD_SIZE is set to 2.> > Regards,> Timmy Brolin> > >
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