A pbuf of PBUF_POOL_BUFSIZE is alloctated for every pbuf_alloc of PBUF_POOL. So PBUF_POOL_BUFSIZE must be the same or larger than any incoming our outgoing packet that’s going to use a pbuf_alloc to obtain a packet buffer. I had a similar problem to yours in not adding ETH_PAD_SIZE (2) to PBUF_POOL_BUFSIZE and every pbuf_alloc for a packet had a chained pbuf with the second pbuf containing the 2 bytes.
PBUF_POOL_BUFSIZE doesn’t constrain the incoming our outgoing packet size – it’s the maximum size that’s going to be used for all PBUF_POOL pbuf_allocs. Bill From: [email protected] [mailto:[email protected]] On Behalf Of Gary Spivey Sent: Wednesday, December 07, 2011 5:47 PM To: Mailing list for lwIP users Subject: Re: [lwip-users] Incoming packet bigger than PBUF_POOL_BUFSIZE Thanks, this doesn’t yet work for me … but it does change the problem and leads me to another question that might help. It appears that the buffer allocate does not give me a buffer of the size requested, but constructs a chain of buffers whose total size is what has been requested. What I have been doing is getting the buffer address and copying the entire received Ethernet buffer into that address. With this change, it seems clear that I cannot do this, but that I have to manage the copy into this chain of buffers. Is there an lwip-provided method to do this, or do I just need to follow the chain myself? I am looking through the documentation, but I haven’t found anything yet. -Gary
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