/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

/*

 * Copyright (c) 2008 University of Washington

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation;

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#ifndef WALL_CLOCK_CLOCK_SYNCHRONIZER_H

#define WALL_CLOCK_CLOCK_SYNCHRONIZER_H

#include "ns3/system-condition.h"

#include "synchronizer.h"

namespace ns3 {

/**

 * @brief Class used for synchronizing the simulation events to a real-time

 * "wall clock" using Posix Clock functions.

 *

 * Enable this synchronizer using:

 *

 *   DefaultValue::Bind ("Synchronizer", "WallClockSynchronizer");

 *

 * before calling any simulator functions.

 *

 * The simulation clock is maintained as a 64-bit integer in a unit specified

 * by the user through the TimeStepPrecision::Set function. This means that

 * it is not possible to specify event expiration times with anything better

 * than this user-specified accuracy.  

 *

 * There are a couple of more issues at this level.  Posix clocks provide

 * access to several clocks we could use as a wall clock.  We don't care about

 * time in the sense of 0430 CEST, we care about some piece of hardware that

 * ticks at some regular period.  The most accurate posix clock in this

 * respect is the CLOCK_PROCESS_CPUTIME_ID clock.  This is a high-resolution

 * register in the CPU.  For example, on Intel machines this corresponds to

 * the timestamp counter (TSC) register.  The resolution of this counter will

 * be on the order of nanoseconds.

 *

 * Now, just because we can measure time in nanoseconds doesn't mean we can

 * put our process to sleep to nanosecond resolution.  We are eventualy going

 * to use the function clock_nanosleep () to sleep until a simulation Time

 * specified by the caller. 

 *

 * MORE ON JIFFIES, SLEEP, PROCESSES, etc., as required

 *

 * Nanosleep takes a struct timespec as an input so we have to deal with

 * conversion between Time and struct timespec here.  They are both 

 * interpreted as elapsed times.

 */

class WallClockSynchronizer : public Synchronizer

{

public:

  WallClockSynchronizer ();

  virtual ~WallClockSynchronizer ();

  static const uint64_t US_PER_NS = (uint64_t)1000;

  static const uint64_t US_PER_SEC = (uint64_t)1000000;

  static const uint64_t NS_PER_SEC = (uint64_t)1000000000;

protected:

/**

 * @brief Return true if this synchronizer is actually synchronizing to a

 * realtime clock.  The simulator sometimes needs to know this.

 *

 * @internal

 *

 * Subclasses are expected to implement this method to tell the outside world

 * whether or not they are synchronizing to a realtime clock.

 *

 * @returns True if locked with realtime, false if not.

 */

  virtual bool DoRealtime (void);

/**

 * @brief Retrieve the value of the origin of the underlying normalized wall

 * clock time in nanosecond units.

 *

 * @internal

 *

 * Subclasses are expected to implement this method to do the actual

 * real-time-clock-specific work of getting the current time.

 *

 * @returns The normalized wall clock time (in nanosecond units).

 * @see TimeStepPrecision::Get

 * @see Synchronizer::SetOrigin

 */

  virtual uint64_t DoGetCurrentRealtime (void);

/**

 * @brief Establish a correspondence between a simulation time and a 

 * wall-clock (real) time.

 *

 * @internal

 *

 * There are three timelines involved here:  the simulation time, the 

 * (absolute) wall-clock time and the (relative) synchronizer real time.

 * Calling this method makes a correspondence between the origin of the

 * synchronizer time and the current wall-clock time.

 *

 * This method is expected to be called at the "instant" before simulation

 * begins.  At this point, simulation time = 0, and synchronizer time is

 * set = 0 in this method.  We then associate this time with the current

 * value of the real time clock that will be used to actually perform the

 * synchronization.

 *

 * Subclasses are expected to implement this method to do the actual 

 * real-time-clock-specific work of making the correspondence mentioned above.

 * for example, this is where the differences between Time parameters and

 * parameters to clock_nanosleep would be dealt with. 

 *

 * @param ns The simulation time we need to use as the origin (normalized to

 * nanosecond units).

 */

  virtual void DoSetOrigin (uint64_t ns);

/**

 * @brief Declaration of method used to retrieve drift between the real time

 * clock used to synchronize the simulation and the current simulation time.

 *

 * @internal

 *

 * @param ns Simulation timestep from the simulator normalized to nanosecond 

 * steps.

 * @returns Drift in nanosecond units.

 * @see TimeStepPrecision::Get

 * @see Synchronizer::SetOrigin

 * @see Synchronizer::GetDrift

 */

  virtual int64_t DoGetDrift (uint64_t ns);

/**

 * @brief Wait until the real time is in sync with the specified simulation

 * time.

 *

 * @internal

 *

 * This is where the real work of synchronization is done.  The Time passed

 * in as a parameter is the simulation time.  The job of Synchronize is to

 * translate from simulation time to synchronizer time (in a perfect world

 * this is the same time) and then figure out how long in real-time it needs

 * to wait until that synchronizer / simulation time comes around.

 *

 * Subclasses are expected to implement this method to do the actual

 * real-time-clock-specific work of waiting (either busy-waiting or sleeping,

 * or some combination) until the requested simulation time.

 *

 * @param ns The simulation time we need to wait for (normalized to nanosecond

 * units).

 * @see TimeStepPrecision::Get

 */

  virtual bool DoSynchronize (uint64_t nsCurrent, uint64_t nsDelay);

  virtual void DoSignal (void);

  virtual void DoSetCondition (bool cond);

  virtual void DoEventStart (void);

  virtual uint64_t DoEventEnd (void);

  bool SpinWait (uint64_t);

  bool SleepWait (uint64_t);

  uint64_t DriftCorrect (uint64_t nsNow, uint64_t nsDelay);

  uint64_t GetRealtime (void);

  uint64_t GetNormalizedRealtime (void);

  void NsToTimeval (int64_t ns, struct timeval *tv);

  uint64_t TimevalToNs (struct timeval *tv);

  void TimevalAdd (

    struct timeval *tv1, 

    struct timeval *tv2,

    struct timeval *result);

  uint64_t m_cpuTick;

  uint64_t m_realtimeTick;

  uint64_t m_jiffy;

  uint64_t m_nsEventStart;

  SystemCondition m_condition;

};

}; // namespace ns3

#endif /* WALL_CLOCK_SYNCHRONIZER_H */