Re: [lwip-users] Managing pbufs for sending UDP

[Sergio R. Caprile]

struct pbuf* p;

        if((p = pbuf_alloc(PBUF_TRANSPORT, MSG_LEN, PBUF_RAM)) == NULL){
                oops...
        }

        // do your stuff on p

        udp_send(pcb, p) or udp_sendto(pcb, p, &ipaddr, DEST_PORT);

        pbuf_free(p);

If you send from static memory, you could use PBUF_ROM

You will use PBUF_POOL on your netif. As far as I understand from the 
docs, fragmentation is "avoided" by using fixed size pbufs that are 
chained when needed to form a bigger pbuf.
As for PBUF_RAM, it is alloced from an lwIP RAM area, it won't mess with 
the rest of the system but I guess it might get fragmented.
Perhaps Simon or one of the developers can shine a light on this.

The docs (they are good friends) recommend you don't use PBUF_POOL for 
tx: 
http://www.nongnu.org/lwip/2_0_x/group__pbuf.html#ggab7e0e32fcc292c0d7107721766ed92fbac9b6ba960fdea6f2e8f35c8313b77e4e