If the driver specific header file
the driver should implement a hardware-specific function matching
this defined prototype.
The function is called when lwIP is releasing a packet buffer, allowing the low-level device driver access to the (now unused) packet buffer. This avoids the overhead of lwIP having to complete the free operation, and for the driver having to make a subsequent allocation call.
If the driver does want to make use of the packet buffer
descriptor (for example, to replace a DMA buffer slot) then it
must call the lwIP
pbuf_pool_reinit() to ensure a
valid descriptor state prior to reuse.
If the driver does not make use of the
struct pbuf then it returns
a value of 1 to indicate that the packet buffer has not been
If the driver does claim the packet buffer then it should return 0 to indicate that the packet buffer descriptor has been reused.