task #7013: Added option LWIP_NETIF_TX_SINGLE_PBUF to try to create transmit packets from only one pbuf to help MACs that don't support scatter-gather DMA.

src/include/lwip/netbuf.h

@@ -65,6 +65,7 @@ void              netbuf_first    (struct netbuf *buf);
 #define netbuf_copy_partial(buf, dataptr, len, offset) \
   pbuf_copy_partial((buf)->p, (dataptr), (len), (offset))
 #define netbuf_copy(buf,dataptr,len) netbuf_copy_partial(buf, dataptr, len, 0)
+#define netbuf_take(buf, dataptr, len) pbuf_take((buf)->p, dataptr, len)
 #define netbuf_len(buf)              ((buf)->p->tot_len)
 #define netbuf_fromaddr(buf)         ((buf)->addr)
 #define netbuf_fromport(buf)         ((buf)->port)

src/include/lwip/opt.h

@@ -965,6 +965,19 @@
 #define LWIP_NETIF_LOOPBACK_MULTITHREADING    (!NO_SYS)
 #endif
 
+/**
+ * LWIP_NETIF_TX_SINGLE_PBUF: if this is set to 1, lwIP tries to put all data
+ * to be sent into one single pbuf. This is for compatibility with DMA-enabled
+ * MACs that do not support scatter-gather.
+ * Beware that this might involve CPU-memcpy before transmitting that would not
+ * be needed without this flag! Use this only if you need to!
+ *
+ * @todo: TCP and IP-frag do not work with this, yet:
+ */
+#ifndef LWIP_NETIF_TX_SINGLE_PBUF
+#define LWIP_NETIF_TX_SINGLE_PBUF             0
+#endif /* LWIP_NETIF_TX_SINGLE_PBUF */
+
 /*
    ------------------------------------
    ---------- LOOPIF options ----------

src/include/lwip/pbuf.h

@@ -110,6 +110,8 @@ void pbuf_chain(struct pbuf *head, struct pbuf *tail);
 struct pbuf *pbuf_dechain(struct pbuf *p);
 err_t pbuf_copy(struct pbuf *p_to, struct pbuf *p_from);
 u16_t pbuf_copy_partial(struct pbuf *p, void *dataptr, u16_t len, u16_t offset);
+err_t pbuf_take(struct pbuf *buf, const void *dataptr, u16_t len);
+struct pbuf *pbuf_coalesce(struct pbuf *p, pbuf_layer layer);
 
 #ifdef __cplusplus
 }