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A simple implicit network time synchronization mechanism

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adamdunkels 2007-12-16 14:29:56 +00:00
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core/sys/timesynch.c Normal file
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/**
* \addtogroup timesynch
* @{
*/
/*
* 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: timesynch.c,v 1.1 2007/12/16 14:29:56 adamdunkels Exp $
*/
/**
* \file
* A simple time synchronization mechanism
* \author
* Adam Dunkels <adam@sics.se>
*/
#include "sys/timesynch.h"
#include "net/rime/rimebuf.h"
#include "net/rime.h"
#include "dev/simple-cc2420.h"
static const struct mac_driver timesynch_driver;
static const struct mac_driver *mac;
static void (* receiver_callback)(const struct mac_driver *);
#include <stdio.h>
static int authority_level;
static rtimer_clock_t offset;
/*---------------------------------------------------------------------------*/
int
timesynch_authority_level(void)
{
return authority_level;
}
/*---------------------------------------------------------------------------*/
void
timesynch_set_authority_level(int level)
{
authority_level = level;
}
/*---------------------------------------------------------------------------*/
rtimer_clock_t
timesynch_time(void)
{
return rtimer_arch_now() + offset;
}
/*---------------------------------------------------------------------------*/
rtimer_clock_t
timesynch_time_to_rtimer(rtimer_clock_t synched_time)
{
return synched_time - offset;
}
/*---------------------------------------------------------------------------*/
rtimer_clock_t
timesynch_offset(void)
{
return offset;
}
/*---------------------------------------------------------------------------*/
static int
send(void)
{
return mac->send();
}
/*---------------------------------------------------------------------------*/
static void
input(const struct mac_driver *d)
{
if(receiver_callback) {
receiver_callback(&timesynch_driver);
}
}
/*---------------------------------------------------------------------------*/
static void
adjust_offset(rtimer_clock_t authoritative_time, rtimer_clock_t local_time)
{
offset = offset + authoritative_time - local_time;
}
/*---------------------------------------------------------------------------*/
static int
read(void)
{
int len;
len = mac->read();
/* We check the authority level of the sender of the incoming
packet. If the sending node has a lower authority level than we
have, we synchronize to the time of the sending node and set our
own authority level to be one more than the sending node. */
if(simple_cc2420_authority_level_of_sender < authority_level) {
adjust_offset(simple_cc2420_time_of_departure +
simple_cc2420_time_for_transmission,
simple_cc2420_time_of_arrival);
if(simple_cc2420_authority_level_of_sender + 1 != authority_level) {
printf("New authority %d, previous %d\n",
simple_cc2420_authority_level_of_sender + 1,
authority_level);
authority_level = simple_cc2420_authority_level_of_sender + 1;
}
/* XXX the authority level should be increased over time except
for the sink node. */
}
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(void)
{
return mac->off();
}
/*---------------------------------------------------------------------------*/
static const struct mac_driver timesynch_driver = {
send,
read,
set_receive_function,
on,
off,
};
/*---------------------------------------------------------------------------*/
const struct mac_driver *
timesynch_init(const struct mac_driver *d)
{
mac = d;
mac->set_receive_function(input);
mac->on();
return &timesynch_driver;
}
/*---------------------------------------------------------------------------*/
/** @} */

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/**
* \addtogroup sys
* @{
*/
/**
* \defgroup timesynch Implicit network time synchronization
* @{
*
* This crude and simple network time synchronization module
* synchronizes clocks of all nodes in a network. The time
* synchronization is implicit in that no explicit time
* synchronization messages are sent: the module relies on the
* underlying network device driver to timestamp all radio messages,
* both outgoing and incoming. The code currently only works on the
* Tmote Sky platform and the simple-cc2420 driver.
*
* Every node has an authority level, which is included in every
* outgoing packet. If a message is received from a node with higher
* authority (lower authority number), the node adjusts its clock
* towards the clock of the sending node.
*
* The timesynch module is implemented as a meta-MAC protocol, so that
* the module is invoked for every incoming packet.
*
*/
/*
* 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: timesynch.h,v 1.1 2007/12/16 14:29:56 adamdunkels Exp $
*/
/**
* \file
* Header file for a simple time synchronization mechanism
* \author
* Adam Dunkels <adam@sics.se>
*/
#ifndef __TIMESYNCH_H__
#define __TIMESYNCH_H__
#include "net/mac/mac.h"
#include "sys/rtimer.h"
/**
* \brief Initialize the timesynch module; should be called during the MAC initialization procedure
* \param r The underlying MAC driver
* \return A pointer to the timesynch module's meta MAC driver
*
* This function initializes the timesynch module. The
* function should be called as part of the MAC
* initialization procedure.
*
*/
const struct mac_driver *timesynch_init(const struct mac_driver *r);
/**
* \brief Get the current time-synchronized time
* \return The current time-synchronized time
*
* This function returns the current time-synchronized
* time.
*
*/
rtimer_clock_t timesynch_time(void);
/**
* \brief Get the current time-synchronized rtimer time, suitable for use with the rtimer module
* \return The current time-synchronized rtimer time
*
* This function returns the (local) rtimer-equivalent
* time corresponding to the current time-synchronized
* (global) time. The rtimer-equivalent time is used for
* setting rtimer timers that are synchronized to other
* nodes in the network.
*
*/
rtimer_clock_t timesynch_time_to_rtimer(rtimer_clock_t synched_time);
/**
* \brief Get the current time-synchronized offset from the rtimer clock, which is used mainly for debugging
* \return The current time-synchronized offset from the rtimer clock
*
* This function returns the current time-synchronized
* offset from the rtimer arch clock. This is mainly
* useful for debugging the timesynch module.
*
*/
rtimer_clock_t timesynch_offset(void);
/**
* \brief Get the current authority level of the time-synchronized time
* \return The current authority level of the time-synchronized time
*
* This function returns the current authority level of
* the time-synchronized time. A node with a lower
* authority level is defined to have a better notion of
* time than a node with a higher authority
* level. Authority level 0 is best and should be used by
* a sink node that has a connection to an outside,
* "true", clock source.
*
*/
int timesynch_authority_level(void);
/**
* \brief Set the authority level of the current time
* \param level The authority level
*/
void timesynch_set_authority_level(int level);
#endif /* __TIMESYNCH_H__ */
/** @} */
/** @} */