csma.c

Go to the documentation of this file.

/*
 * Copyright (c) 2010, 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 1.27 2011/01/25 14:24:38 adamdunkels Exp $
 */

/**
 * \file
 *         A Carrier Sense Multiple Access (CSMA) MAC layer
 * \author
 *         Adam Dunkels <adam@sics.se>
 */

#include "net/mac/csma.h"
#include "net/packetbuf.h"
#include "net/queuebuf.h"

#include "sys/ctimer.h"

#include "lib/random.h"

#include "net/netstack.h"

#include "lib/list.h"
#include "lib/memb.h"

#include <string.h>

#include <stdio.h>

#define DEBUG 0
#if DEBUG
#include <stdio.h>
#define PRINTF(...) printf(__VA_ARGS__)
#else /* DEBUG */
#define PRINTF(...)
#endif /* DEBUG */

#ifndef CSMA_MAX_MAC_TRANSMISSIONS
#ifdef CSMA_CONF_MAX_MAC_TRANSMISSIONS
#define CSMA_MAX_MAC_TRANSMISSIONS CSMA_CONF_MAX_MAC_TRANSMISSIONS
#else
#define CSMA_MAX_MAC_TRANSMISSIONS 3
#endif /* CSMA_CONF_MAX_MAC_TRANSMISSIONS */
#endif /* CSMA_MAX_MAC_TRANSMISSIONS */

#if CSMA_MAX_MAC_TRANSMISSIONS < 1
#error CSMA_CONF_MAX_MAC_TRANSMISSIONS must be at least 1.
#error Change CSMA_CONF_MAX_MAC_TRANSMISSIONS in contiki-conf.h or in your Makefile.
#endif /* CSMA_CONF_MAX_MAC_TRANSMISSIONS < 1 */

struct queued_packet {
  struct queued_packet *next;
  struct queuebuf *buf;
  /*  struct ctimer retransmit_timer;*/
  mac_callback_t sent;
  void *cptr;
  uint8_t transmissions, max_transmissions;
  uint8_t collisions, deferrals;
};

#define MAX_QUEUED_PACKETS 6
MEMB(packet_memb, struct queued_packet, MAX_QUEUED_PACKETS);
LIST(queued_packet_list);

static struct ctimer transmit_timer;

static uint8_t rdc_is_transmitting;

static void packet_sent(void *ptr, int status, int num_transmissions);

/*---------------------------------------------------------------------------*/
static clock_time_t
default_timebase(void)
{
  clock_time_t time;
  /* The retransmission time must be proportional to the channel
     check interval of the underlying radio duty cycling layer. */
  time = NETSTACK_RDC.channel_check_interval();

  /* If the radio duty cycle has no channel check interval (i.e., it
     does not turn the radio off), we make the retransmission time
     proportional to the configured MAC channel check rate. */
  if(time == 0) {
    time = CLOCK_SECOND / NETSTACK_RDC_CHANNEL_CHECK_RATE;
  }
  return time;
}
/*---------------------------------------------------------------------------*/
static void
transmit_queued_packet(void *ptr)
{
  /*  struct queued_packet *q = ptr;*/
  struct queued_packet *q;

  /* Don't transmit a packet if the RDC is still transmitting the
     previous one. */
  if(rdc_is_transmitting) {
    return;
  }
  
  //  printf("q %d\n", list_length(queued_packet_list));

  q = list_head(queued_packet_list);

  if(q != NULL) {
    queuebuf_to_packetbuf(q->buf);
    PRINTF("csma: sending number %d %p, queue len %d\n", q->transmissions, q,
           list_length(queued_packet_list));
    //    printf("s %d\n", packetbuf_addr(PACKETBUF_ADDR_RECEIVER)->u8[0]);
    rdc_is_transmitting = 1;
    NETSTACK_RDC.send(packet_sent, q);
  }
}
/*---------------------------------------------------------------------------*/
static void
start_transmission_timer(void)
{
  PRINTF("csma: start_transmission_timer, queue len %d\n",
         list_length(queued_packet_list));
  if(list_length(queued_packet_list) > 0) {
    if(ctimer_expired(&transmit_timer)) {
      ctimer_set(&transmit_timer, 0,
                 transmit_queued_packet, NULL);
    }
  }
}
/*---------------------------------------------------------------------------*/
static void
free_queued_packet(void)
{
  struct queued_packet *q;

  //  printf("q %d\n", list_length(queued_packet_list));

  q = list_head(queued_packet_list);

  if(q != NULL) {
    queuebuf_free(q->buf);
    list_remove(queued_packet_list, q);
    memb_free(&packet_memb, q);
    PRINTF("csma: free_queued_packet, queue length %d\n",
           list_length(queued_packet_list));
    if(list_length(queued_packet_list) > 0) {
      ctimer_set(&transmit_timer, default_timebase(), transmit_queued_packet, NULL);
    }
  }
}
/*---------------------------------------------------------------------------*/
static void
packet_sent(void *ptr, int status, int num_transmissions)
{
  struct queued_packet *q = ptr;
  clock_time_t time = 0;
  mac_callback_t sent;
  void *cptr;
  int num_tx;
  int backoff_transmissions;

  rdc_is_transmitting = 0;
  
  switch(status) {
  case MAC_TX_OK:
  case MAC_TX_NOACK:
    q->transmissions++;
    break;
  case MAC_TX_COLLISION:
    q->collisions++;
    break;
  case MAC_TX_DEFERRED:
    q->deferrals++;
    break;
  }

  sent = q->sent;
  cptr = q->cptr;
  num_tx = q->transmissions;
  
  if(status == MAC_TX_COLLISION ||
     status == MAC_TX_NOACK) {

    /* If the transmission was not performed because of a collision or
       noack, we must retransmit the packet. */
    
    switch(status) {
    case MAC_TX_COLLISION:
      PRINTF("csma: rexmit collision %d\n", q->transmissions);
      break;
    case MAC_TX_NOACK:
      PRINTF("csma: rexmit noack %d\n", q->transmissions);
      break;
    default:
      PRINTF("csma: rexmit err %d, %d\n", status, q->transmissions);
    }

    /* The retransmission time must be proportional to the channel
       check interval of the underlying radio duty cycling layer. */
    time = default_timebase();

    /* The retransmission time uses a linear backoff so that the
       interval between the transmissions increase with each
       retransmit. */
    backoff_transmissions = q->transmissions + 1;

    /* Clamp the number of backoffs so that we don't get a too long
       timeout here, since that will delay all packets in the
       queue. */
    if(backoff_transmissions > 3) {
      backoff_transmissions = 3;
    }
    time = time + (random_rand() % (backoff_transmissions * time));

    if(q->transmissions < q->max_transmissions) {
      PRINTF("csma: retransmitting with time %lu %p\n", time, q);
      ctimer_set(&transmit_timer, time,
                 transmit_queued_packet, NULL);
    } else {
      PRINTF("csma: drop with status %d after %d transmissions, %d collisions\n",
             status, q->transmissions, q->collisions);
      /*      queuebuf_to_packetbuf(q->buf);*/
      free_queued_packet();
      mac_call_sent_callback(sent, cptr, status, num_tx);
    }
  } else {
    if(status == MAC_TX_OK) {
      PRINTF("csma: rexmit ok %d\n", q->transmissions);
    } else {
      PRINTF("csma: rexmit failed %d: %d\n", q->transmissions, status);
    }
    /*    queuebuf_to_packetbuf(q->buf);*/
    free_queued_packet();
    mac_call_sent_callback(sent, cptr, status, num_tx);
  }
}
/*---------------------------------------------------------------------------*/
static void
send_packet(mac_callback_t sent, void *ptr)
{
  struct queued_packet *q;
  static uint16_t seqno;
  
  packetbuf_set_attr(PACKETBUF_ATTR_MAC_SEQNO, seqno++);
  
  /* If the packet is a broadcast, do not allocate a queue
     entry. Instead, just send it out.  */
  if(!rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
                   &rimeaddr_null)) {

    /* Remember packet for later. */
    q = memb_alloc(&packet_memb);
    if(q != NULL) {
      q->buf = queuebuf_new_from_packetbuf();
      if(q->buf != NULL) {
        if(packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS) == 0) {
          /* Use default configuration for max transmissions */
          q->max_transmissions = CSMA_MAX_MAC_TRANSMISSIONS;
        } else {
          q->max_transmissions =
            packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS);
        }
        q->transmissions = 0;
        q->collisions = 0;
        q->deferrals = 0;
        q->sent = sent;
        q->cptr = ptr;
        if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
           PACKETBUF_ATTR_PACKET_TYPE_ACK) {
          list_push(queued_packet_list, q);
        } else {
          list_add(queued_packet_list, q);
        }
        start_transmission_timer();
        return;
      }
      memb_free(&packet_memb, q);
      PRINTF("csma: could not allocate queuebuf, will drop if collision or noack\n");
    }
    PRINTF("csma: could not allocate memb, will drop if collision or noack\n");
  } else {
    PRINTF("csma: send broadcast (%d) or without retransmissions (%d)\n",
           !rimeaddr_cmp(packetbuf_addr(PACKETBUF_ADDR_RECEIVER),
                         &rimeaddr_null),
           packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS));
  }
  NETSTACK_RDC.send(sent, ptr);
}
/*---------------------------------------------------------------------------*/
static void
input_packet(void)
{
  NETSTACK_NETWORK.input();
}
/*---------------------------------------------------------------------------*/
static int
on(void)
{
  return NETSTACK_RDC.on();
}
/*---------------------------------------------------------------------------*/
static int
off(int keep_radio_on)
{
  return NETSTACK_RDC.off(keep_radio_on);
}
/*---------------------------------------------------------------------------*/
static unsigned short
channel_check_interval(void)
{
  if(NETSTACK_RDC.channel_check_interval) {
    return NETSTACK_RDC.channel_check_interval();
  }
  return 0;
}
/*---------------------------------------------------------------------------*/
static void
init(void)
{
  memb_init(&packet_memb);
  rdc_is_transmitting = 0;
}
/*---------------------------------------------------------------------------*/
const struct mac_driver csma_driver = {
  "CSMA",
  init,
  send_packet,
  input_packet,
  on,
  off,
  channel_check_interval,
};
/*---------------------------------------------------------------------------*/