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

[address@hidden]

> BDs (Buffer Descriptors) are a sequential list of 2-word (8 byte) entries
> that contain status that the program and hardware update, the buffer length,
> and a pointer to the buffer.  The last BD has a bit marking the last and the
> PowerPC has a register to know the first. It can cycle through the BDs using
> buffers as needed.  It checks each BD status for the next free one and
> stores the packet into memory pointed to by the BD.  The program clears a
> bit when it's done with a buffer and the PPC sets the bit when it's filled a
> buffer.  It's a pretty cool mechanism I've not seen before.
Isn't that normal BD behaviour? Anyway, the opencores MAC does it that 
way, too. What you have to do is allocate one PBUF_POOL that has the 
size of the maximum received ETH frame for each BD. When one BD changes 
to 'received', use the address stored in the BD to get back the pbuf 
pointer (will be ~16 bytes below for PBUF_POOLs), allocate a fresh 
PBUF_POOL, store its payload address into the BD and set it as available 
again. At this point, you have the BD available for receiving again and 
can pass the previous PBUF_POOL into the stack (without copying at all)!

Simon