Added an optimization option that avoids multiple simultaneous broadcasts from neighbors: when a broadcast is to be sent, a sender does not send until it knows that no other nodes are broadcasting.

core/net/mac/lpp.c

@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: lpp.c,v 1.21 2009/05/06 15:06:38 adamdunkels Exp $
+ * $Id: lpp.c,v 1.22 2009/05/10 21:09:05 adamdunkels Exp $
  */
 
 /**
@@ -78,6 +78,7 @@
 #define WITH_PROBE_AFTER_TRANSMISSION 0
 #define WITH_ENCOUNTER_OPTIMIZATION   1
 #define WITH_ADAPTIVE_OFF_TIME        0
+#define WITH_PENDING_BROADCAST        1
 
 #ifdef LPP_CONF_LISTEN_TIME
 #define LISTEN_TIME LPP_CONF_LISTEN_TIME
@@ -150,10 +151,17 @@ static clock_time_t off_time = OFF_TIME;
 struct queue_list_item {
   struct queue_list_item *next;
   struct queuebuf *packet;
-  struct ctimer timer;
+  struct ctimer removal_timer;
   struct compower_activity compower;
+#if WITH_PENDING_BROADCAST
+  uint8_t broadcast_flag;
+#endif /* WITH_PENDING_BROADCAST */
 };
 
+#define BROADCAST_FLAG_NONE    0
+#define BROADCAST_FLAG_WAITING 1
+#define BROADCAST_FLAG_PENDING 2
+#define BROADCAST_FLAG_SEND    3
 
 LIST(pending_packets_list);
 LIST(queued_packets_list);
@@ -250,9 +258,11 @@ turn_radio_on_for_neighbor(rimeaddr_t *neighbor, struct queue_list_item *i)
   struct encounter *e;
 
   if(rimeaddr_cmp(neighbor, &rimeaddr_null)) {
+#if ! WITH_PENDING_BROADCAST
     /* We have been asked to turn on the radio for a broadcast, so we
        just turn on the radio. */
     turn_radio_on();
+#endif /* ! WITH_PENDING_BROADCAST */
     list_add(queued_packets_list, i);
     return;
   }
@@ -313,7 +323,7 @@ remove_queued_packet(void *item)
 	 rimeaddr_node_addr.u8[0], rimeaddr_node_addr.u8[1]);
 
   
-  ctimer_stop(&i->timer);  
+  ctimer_stop(&i->removal_timer);  
   queuebuf_free(i->packet);
   list_remove(pending_packets_list, i);
   list_remove(queued_packets_list, i);
@@ -327,6 +337,15 @@ remove_queued_packet(void *item)
   memb_free(&queued_packets_memb, i);
 }
 /*---------------------------------------------------------------------------*/
+#if WITH_PENDING_BROADCAST
+static void
+set_broadcast_flag(struct queue_list_item *i, uint8_t flag)
+{
+  i->broadcast_flag = flag;
+  ctimer_set(&i->removal_timer, PACKET_LIFETIME, remove_queued_packet, i);
+}
+#endif /* WITH_PENDING_BROADCAST */
+/*---------------------------------------------------------------------------*/
 static void
 listen_callback(int periods)
 {
@@ -379,6 +398,25 @@ send_probe(void)
   compower_accumulate(&compower_idle_activity);
 }
 /*---------------------------------------------------------------------------*/
+static int
+num_packets_to_send(void)
+{
+#if WITH_PENDING_BROADCAST
+  struct queue_list_item *i;
+  int num = 0;
+  
+  for(i = list_head(queued_packets_list); i != NULL; i = i->next) {
+    if(i->broadcast_flag == BROADCAST_FLAG_SEND ||
+       i->broadcast_flag == BROADCAST_FLAG_NONE) {
+      ++num;
+    }
+  }
+  return num;
+#else /* WITH_PENDING_BROADCAST */
+  return list_length(queued_packets_list);
+#endif /* WITH_PENDING_BROADCAST */
+}
+/*---------------------------------------------------------------------------*/
 /**
  * Duty cycle the radio and send probes. This function is called
  * repeatedly by a ctimer. The function restart_dutycycle() is used to
@@ -393,6 +431,22 @@ dutycycle(void *ptr)
 
   while(1) {
 
+#if WITH_PENDING_BROADCAST
+    {
+	struct queue_list_item *p;
+	/* Before sending the probe, we mark all broadcast packets in
+	   our output queue to be pending. This means that they are
+	   ready to be sent, once we know that no neighbor is
+	   currently broadcasting. */
+	for(p = list_head(queued_packets_list); p != NULL; p = p->next) {
+	  if(p->broadcast_flag == BROADCAST_FLAG_WAITING) {
+	    PRINTF("wait -> pending\n");
+	    set_broadcast_flag(p, BROADCAST_FLAG_PENDING);
+	  }
+	}
+      }
+#endif /* WITH_PENDING_BROADCAST */
+
     /* Send a probe packet. */
     send_probe();
     
@@ -404,11 +458,28 @@ dutycycle(void *ptr)
     ctimer_set(t, LISTEN_TIME, (void (*)(void *))dutycycle, t);
     PT_YIELD(&dutycycle_pt);
 
+#if WITH_PENDING_BROADCAST
+    {
+      struct queue_list_item *p;
+      /* Go through the list of packets we are waiting to send, and
+	 check if there are any pending broadcasts in the list. If
+	 there are pending broadcasts, and we did not receive any
+	 broadcast packets from a neighbor in response to our probe,
+	 we mark the broadcasts as being ready to send. */
+      for(p = list_head(queued_packets_list); p != NULL; p = p->next) {
+	if(p->broadcast_flag == BROADCAST_FLAG_PENDING) {
+	  PRINTF("pending -> send\n");
+	  set_broadcast_flag(p, BROADCAST_FLAG_SEND);
+	  turn_radio_on();
+	}
+      }
+    }
+#endif /* WITH_PENDING_BROADCAST */
+
     /* If we have no packets to send (indicated by the list length of
        queued_packets_list being zero), we should turn the radio
        off. Othersize, we keep the radio on. */
-    
+    if(num_packets_to_send() == 0) {
-    if(list_length(queued_packets_list) == 0) {
       
       /* If we are not listening for announcements, we turn the radio
 	 off and wait until we send the next probe. */
@@ -427,11 +498,15 @@ dutycycle(void *ptr)
 #endif /* WITH_ADAPTIVE_OFF_TIME */
 
       } else {
+	/* We are listening for annonucements, so we count down the
+	   listen time, and keep the radio on. */
 	is_listening--;
 	ctimer_set(t, OFF_TIME, (void (*)(void *))dutycycle, t);
 	PT_YIELD(&dutycycle_pt);
       }
     } else {
+      /* We had pending packets to send, so we do not turn the radio off. */
+
       ctimer_set(t, off_time, (void (*)(void *))dutycycle, t);
       PT_YIELD(&dutycycle_pt);
     }
@@ -466,9 +541,13 @@ send_packet(void)
 {
   struct lpp_hdr hdr;
   clock_time_t timeout;
+  uint8_t is_broadcast = 0;
 
   rimeaddr_copy(&hdr.sender, &rimeaddr_node_addr);
   rimeaddr_copy(&hdr.receiver, packetbuf_addr(PACKETBUF_ADDR_RECEIVER));
+  if(rimeaddr_cmp(&hdr.receiver, &rimeaddr_null)) {
+    is_broadcast = 1;
+  }
   hdr.type = TYPE_DATA;
 
   packetbuf_hdralloc(sizeof(struct lpp_hdr));
@@ -501,17 +580,33 @@ send_packet(void)
 	memb_free(&queued_packets_memb, i);
 	return 0;
       } else {
-
+        if(is_broadcast) {
-        timeout = UNICAST_TIMEOUT;
-        if(rimeaddr_cmp(&hdr.receiver, &rimeaddr_null)) {
           timeout = PACKET_LIFETIME;
+#if WITH_PENDING_BROADCAST
+	  /* We set the broadcast state of the packet to be
+	     waiting. This means that the packet is waiting for our
+	     next probe to be sent. Our next probe is used to check if
+	     there are any neighbors currently broadcasting a
+	     packet. If so, we will get a broadcast packet in response
+	     to our probe. If no broadcast packet is received in
+	     response to our probe, we mark the packet as ready to be
+	     sent. */
+	  set_broadcast_flag(i, BROADCAST_FLAG_WAITING);
+	  PRINTF("-> waiting\n");
+#endif /* WITH_PENDING_BROADCAST */
+        } else {
+	  timeout = UNICAST_TIMEOUT;
+#if WITH_PENDING_BROADCAST
+	  i->broadcast_flag = BROADCAST_FLAG_NONE;
+#endif /* WITH_PENDING_BROADCAST */
 	}
-	ctimer_set(&i->timer, timeout, remove_queued_packet, i);
+	ctimer_set(&i->removal_timer, timeout, remove_queued_packet, i);
 
 	/* Wait for a probe packet from a neighbor. The actual packet
 	   transmission is handled by the read_packet() function,
 	   which receives the probe from the neighbor. */
         turn_radio_on_for_neighbor(&hdr.receiver, i);
+
       }
     }
   }
@@ -540,6 +635,7 @@ read_packet(void)
     hdr = packetbuf_dataptr();
     packetbuf_hdrreduce(sizeof(struct lpp_hdr));
     /*    PRINTF("got packet type %d\n", hdr->type);*/
+
     if(hdr->type == TYPE_PROBE) {
       /* Parse incoming announcements */
       struct announcement_msg *adata = packetbuf_dataptr();
@@ -560,8 +656,13 @@ read_packet(void)
 			   adata->data[i].value);
       }
 
+      /* Register the encounter with the sending node. We now know the
+	 neighbor's phase. */
       register_encounter(&hdr->sender, reception_time);
 
+      /* Go through the list of packets to be sent to see if any of
+	 them match the sender of the probe, or if they are a
+	 broadcast packet that should be sent. */
       if(list_length(queued_packets_list) > 0) {
 	struct queue_list_item *i;
 	for(i = list_head(queued_packets_list); i != NULL; i = i->next) {
@@ -570,14 +671,33 @@ read_packet(void)
 	  qhdr = queuebuf_dataptr(i->packet);
 	  if(rimeaddr_cmp(&qhdr->receiver, &hdr->sender) ||
 	      rimeaddr_cmp(&qhdr->receiver, &rimeaddr_null)) {
-	    PRINTF("%d.%d: got a probe from %d.%d, sending packet to %d.%d\n",
+	    queuebuf_to_packetbuf(i->packet);
+
+#if WITH_PENDING_BROADCAST
+	    if(i->broadcast_flag == BROADCAST_FLAG_NONE ||
+	       i->broadcast_flag == BROADCAST_FLAG_SEND) {
+	      radio->send(queuebuf_dataptr(i->packet),
+			  queuebuf_datalen(i->packet));
+	      PRINTF("%d.%d: got a probe from %d.%d, sent packet to %d.%d\n",
 		   rimeaddr_node_addr.u8[0], rimeaddr_node_addr.u8[1],
 		     hdr->sender.u8[0], hdr->sender.u8[1],
 		     qhdr->receiver.u8[0], qhdr->receiver.u8[1]);
-	    queuebuf_to_packetbuf(i->packet);
 	      
+	    } else {
+	      PRINTF("%d.%d: got a probe from %d.%d, did not send packet\n",
+		     rimeaddr_node_addr.u8[0], rimeaddr_node_addr.u8[1],
+		     hdr->sender.u8[0], hdr->sender.u8[1]);
+	    }
+#else /* WITH_PENDING_BROADCAST */
 	    radio->send(queuebuf_dataptr(i->packet),
 			queuebuf_datalen(i->packet));
+	    PRINTF("%d.%d: got a probe from %d.%d, sent packet to %d.%d\n",
+		   rimeaddr_node_addr.u8[0], rimeaddr_node_addr.u8[1],
+		   hdr->sender.u8[0], hdr->sender.u8[1],
+		   qhdr->receiver.u8[0], qhdr->receiver.u8[1]);
+#endif /* WITH_PENDING_BROADCAST */
+
+
 
 	    /* Attribute the energy spent on listening for the probe
 	       to this packet transmission. */
@@ -626,6 +746,27 @@ read_packet(void)
 	 for the next packet. */
       compower_clear(&current_packet);
 
+#if WITH_PENDING_BROADCAST
+      if(rimeaddr_cmp(&hdr->receiver, &rimeaddr_null)) {
+	/* This is a broadcast packet. Check the list of pending
+	   packets to see if we are currently sending a broadcast. If
+	   so, we refrain from sending our broadcast until one sleep
+	   cycle period, so that the other broadcaster will have
+	   finished sending. */
+	
+	struct queue_list_item *i;
+	for(i = list_head(queued_packets_list); i != NULL; i = i->next) {
+	  /* If the packet is a broadcast packet that is not yet
+	     ready to be sent, we do not send it. */
+	  if(i->broadcast_flag == BROADCAST_FLAG_PENDING) {
+	    PRINTF("Someone else is sending, pending -> waiting\n");
+	    set_broadcast_flag(i, BROADCAST_FLAG_WAITING);
+	  }
+	}
+      }
+#endif /* WITH_PENDING_BROADCAST */
+	    
+      
 #if WITH_PROBE_AFTER_RECEPTION
       /* XXX send probe after receiving a packet to facilitate data
         streaming. We must first copy the contents of the packetbuf into