Added a simple CSMA (Carrier Sense Multiple Access) mechanism that

works on top of an underlying duty cycling mechanism. The CSMA layer
retransmits packets that could not be sent because of a collision was
detected.

core/net/mac/Makefile.mac

@@ -1,2 +1,2 @@
 CONTIKI_SOURCEFILES += xmac.c nullmac.c lpp.c frame802154.c sicslowmac.c
-CONTIKI_SOURCEFILES += framer.c framer-nullmac.c framer-802154.c
+CONTIKI_SOURCEFILES += framer.c framer-nullmac.c framer-802154.c csma.c

core/net/mac/csma.c

@@ -0,0 +1,206 @@
+/*
+ * Copyright (c) 2007, Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * This file is part of the Contiki operating system.
+ *
+ * $Id: csma.c,v 1.1 2010/01/25 11:46:44 adamdunkels Exp $
+ */
+
+/**
+ * \file
+ *         A MAC 
+ * \author
+ *         Adam Dunkels <adam@sics.se>
+ */
+
+#define CSMA_CONF_REXMIT 1
+
+#include "net/mac/csma.h"
+#include "net/rime/packetbuf.h"
+#include "net/rime/queuebuf.h"
+#include "net/rime/ctimer.h"
+
+#include "lib/random.h"
+
+#include "lib/list.h"
+#include "lib/memb.h"
+
+struct queued_packet {
+  struct queued_packet *next;
+  struct queuebuf *buf;
+  struct ctimer retransmit_timer;
+  uint8_t retransmits;
+};
+
+#define MAX_QUEUED_PACKETS 4
+LIST(packet_list);
+MEMB(packet_memb, struct queued_packet, MAX_QUEUED_PACKETS);
+
+static const struct mac_driver *mac;
+static void (* receiver_callback)(const struct mac_driver *);
+
+const struct mac_driver *csma_init(const struct mac_driver *psc);
+
+/*---------------------------------------------------------------------------*/
+#if CSMA_CONF_REXMIT
+static void
+retransmit_packet(void *ptr)
+{
+  int ret;
+  struct queued_packet *q = ptr;
+
+  queuebuf_to_packetbuf(q->buf);
+  ret = mac->send();
+
+  queuebuf_free(q->buf);
+  list_remove(packet_list, q);
+  memb_free(&packet_memb, q);
+}
+/*---------------------------------------------------------------------------*/
+static int
+send_packet(void)
+{
+  struct queuebuf *buf;
+  int ret;
+  clock_time_t time;
+  rimeaddr_t receiver;
+
+  /* Remember packet for later. */
+  rimeaddr_copy(&receiver, packetbuf_addr(PACKETBUF_ADDR_RECEIVER));
+  buf = queuebuf_new_from_packetbuf();
+  ret = mac->send();
+  /*  if(ret != MAC_TX_OK) {
+    printf("CSMA: err %d\n", ret);
+    }*/
+
+  /* Check if we saw a collission, and if we have a queuebuf with the
+     packet available. Only retransmit unicast packets. Retransmit
+     only once, for now. */
+  if(ret == MAC_TX_COLLISION && buf != NULL &&
+     !rimeaddr_cmp(&receiver, &rimeaddr_null)) {
+    struct queued_packet *q;
+
+    q = memb_alloc(&packet_memb);
+    if(q == NULL) {
+      queuebuf_free(buf);
+      return ret;
+    }
+    q->buf = buf;
+    q->retransmits = 0;
+
+    time = mac->channel_check_interval();
+    if(time == 0) {
+      time = CLOCK_SECOND;
+    }
+    time = time + (random_rand() % (3 * time));
+    
+    ctimer_set(&q->retransmit_timer, time,
+	       retransmit_packet, q);
+    list_add(packet_list, q);
+  }
+  queuebuf_free(buf);
+  return ret;
+}
+#else /* CSMA_CONF_REXMIT */
+static int
+send_packet(void)
+{
+  return mac->send();
+}
+#endif /* CSMA_CONF_REXMIT */
+/*---------------------------------------------------------------------------*/
+static void
+input_packet(const struct mac_driver *d)
+{
+  if(receiver_callback) {
+    receiver_callback(&csma_driver);
+  }
+}
+/*---------------------------------------------------------------------------*/
+static int
+read_packet(void)
+{
+  int len;
+  len = mac->read();
+  return len;
+}
+/*---------------------------------------------------------------------------*/
+static void
+set_receive_function(void (* recv)(const struct mac_driver *))
+{
+  receiver_callback = recv;
+}
+/*---------------------------------------------------------------------------*/
+static int
+on(void)
+{
+  return mac->on();
+}
+/*---------------------------------------------------------------------------*/
+static int
+off(int keep_radio_on)
+{
+  return mac->off(keep_radio_on);
+}
+/*---------------------------------------------------------------------------*/
+static unsigned short
+channel_check_interval(void)
+{
+  if(mac->channel_check_interval) {
+    return mac->channel_check_interval();
+  }
+  return 0;
+}
+/*---------------------------------------------------------------------------*/
+#define NAMEBUF_LEN 16
+static char namebuf[NAMEBUF_LEN];
+const struct mac_driver csma_driver = {
+  namebuf,
+  csma_init,
+  send_packet,
+  read_packet,
+  set_receive_function,
+  on,
+  off,
+  channel_check_interval,
+};
+/*---------------------------------------------------------------------------*/
+const struct mac_driver *
+csma_init(const struct mac_driver *psc)
+{
+  memb_init(&packet_memb);
+  list_init(packet_list);
+  mac = psc;
+  mac->set_receive_function(input_packet);
+  /*  printf("CSMA with MAC %s, channel check rate %d Hz\n", mac->name,
+      CLOCK_SECOND / channel_check_interval());*/
+  memcpy(namebuf, "CSMA ", 5);
+  memcpy(namebuf + 5, psc->name, NAMEBUF_LEN - 6);
+  return &csma_driver;
+}
+/*---------------------------------------------------------------------------*/

core/net/mac/csma.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (c) 2007, Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * This file is part of the Contiki operating system.
+ *
+ * $Id: csma.h,v 1.1 2010/01/25 11:46:44 adamdunkels Exp $
+ */
+
+/**
+ * \file
+ *         A MAC stack protocol that performs retransmissions when the
+ *         underlying MAC layer has problems with collisions
+ * \author
+ *         Adam Dunkels <adam@sics.se>
+ */
+
+#ifndef __CSMA_H__
+#define __CSMA_H__
+
+#include "net/mac/mac.h"
+#include "dev/radio.h"
+
+extern const struct mac_driver csma_driver;
+
+const struct mac_driver *csma_init(const struct mac_driver *r);
+
+#endif /* __CSMA_H__ */