Re: [lwip-users] Understanding pbuf's

[address@hidden]

Martin Osterloh wrote:
> My NIC driver provides an interrupt function that is called every time 
> a frame is received.
> My intuition tells me that I have to allocate a pbuf now (of the 
> frame's length).
>
> But how do i actually fill in the blanks in the pbufs (in case there 
> is a chain).
Basically, there are 2 approaches:
a) in the interupt, call pbuf_alloc(PBUF_POOL) and copy the received 
data into the pbuf chain by copying into each pbuf until all data is 
copied - this method is to be used for non-DMA enabled MACs where you 
have to use memcpy() anyway.
b) pre-allocate pbufs and set up your MAC-DMA engine to directly put the 
RX data into p->payload - ATTENTION: if your MAC doesn't support 
scattering a packet among multiple regions, PBUF_POOL pbufs must be big 
enough to hold a complete packet.

... and that's it... aside from ensuring SYS_ARCH_PROTECT is correctly 
set up to protect pbuf_alloc() against them main loop (if you call it 
from an ISR).

Hope that helps,
Simon