Allocate the pbuf large enough to handle worst case alignment and align its payload after the allocation. I do this on the PPC (8349) with Receive Buffers that must be 64 byte-aligned. I added an LWIP_ASSERT on the payload & 0x3F being 0 to be sure I had it right. I store the payload into the Rx BD and keep a pointer to the pbuf in a static array whose index is the same as the Rx BD.
Bill From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Muhamad Ikhwan Ismail Sent: Friday, May 09, 2008 9:10 AM To: [email protected] Subject: [lwip-users] Misalignment problems on PowerPC (little endian mode) Hi, I am interested in knowing if there is any other user of lwip who has managed to implement lwip in PowerPC (little endian mode) and got rid of the lil endian misalignment exceptions ? As lwip strips the Ethernet header (14 bytes) the IP addr fields (4 bytes) in the IP header sits on a non-aligned address.My FEC is setup in a way that all received buffers are stored directly into the pbufs instead of a temporary buffer to minimize latency, so the ethernet padding option does not really work for me. The FEC can only save frames into addresses multiple of 16 only. So for me (as far as my knowledge limits me :) ) there 2 other possibilities left, one is packing the structure, or apply changes on the ip address functions and macros so that it works with the ip address as 2 16 bit fields instead of 1 32 bits field. Unfortunately I couldnt make structure packing work with my compiler (Wind River Compiler). I am interested in knowing if anyone has done the same thing and mind sharing experience ? Any thoughts,ideas and feedbacks would also be welcomed. ps: I have an alignment fixing subroutine, but then again we want to minimize the latency. Greetings and thanks in advance Ikhwan Ismail ABB STOTZ-KONTAKT GmbH Heidelberg Germany _____ Stay in touch when you're away with Windows Live Messenger. IM anytime you're online. <http://www.windowslive.com/messenger/overview.html?ocid=TXT_TAGLM_WL_Refres h_messenger_052008>
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