RE: [lwip-users] Transferring large data fast and pointing pbufs directly to Ethernet receive buffers

[Bill Auerbach]

> This sounds very similar to the buffer descriptors on the Atmel
> AT91SAM7X chips that I'm using. Like Jonathan was saying, there are some
> changes being tossed around for changing the way pbuf's work that should
> make something like this more elegant.
> 
> For now, this is how I solved the problem:
> 
> I use in lwipopts:
> #define PBUF_POOL_SIZE          100   // Allows for about 8 full-size
> (1500 byte) packets
> #define PBUF_POOL_BUFSIZE       128 // The receive descriptors are fixed
> at 128 bytes
> 
> I fill the buffer descriptor table with 32 empty pbuf's from this pool
> (setting the table entry to point to the pbuf payload itself, so a
> couple words after the start of the pointer I get back from pbuf_alloc).
> As packets come in, I pull them out of the descriptor table, chain them
> together, and then send it up the stack (no copy necessary). I replace
> their entries with fresh pbuf's from the pool. When the pbuf is freed
> after the application is done, then it gets put back in the pool.

Jared, you and Simon straightened me out, finally.  It's seems so obvious
now - changing the BD to point to a new pbuf and sending the previous one on
for processing which will be freed when it's done is perfect.  I was in the
wrong mindset of thinking the BDs were static.

Thank you again!

Bill