gem5/src/sim/root.hh

/*
 * Copyright (c) 2020 ARM Limited
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 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
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 * terms below provided that you ensure that this notice is replicated
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 * modified or unmodified, in source code or in binary form.
 *
 * Copyright (c) 2011 Advanced Micro Devices, Inc.
 * All rights reserved.
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 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
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/**
 * @file This file defines the Root simobject and the methods used to control
 * the time syncing mechanism provided through it.
 *
 * Time syncing prevents simulated time from passing faster than real time. It
 * works by scheduling a periodic event that checks to see if its simulated
 * period is shorter than its real period. If it is, it stalls the simulation
 * until they're equal.
 */

#ifndef __SIM_ROOT_HH__
#define __SIM_ROOT_HH__

#include "base/statistics.hh"
#include "base/time.hh"
#include "base/types.hh"
#include "params/Root.hh"
#include "sim/eventq.hh"
#include "sim/globals.hh"
#include "sim/sim_object.hh"

namespace gem5
{

class Root : public SimObject
{
  private:
    static Root *_root;

  protected:
    bool _enabled;
    Time _period;
    Tick _periodTick;
    Time _spinThreshold;

    Time lastTime;

    Globals globals;

    void timeSync();
    EventFunctionWrapper syncEvent;

  public:
    /**
     * Use this function to get a pointer to the single Root object in the
     * simulation. This function asserts that such an object has actual been
     * constructed to avoid having to perform that check everywhere the root
     * is used. This is to allow calling the functions below.
     *
     * @return Pointer to the single root object.
     */
    static Root *
    root()
    {
        assert(_root);
        return _root;
    }

  public: // Global statistics
    struct RootStats : public statistics::Group
    {
        void resetStats() override;

        statistics::Formula simSeconds;
        statistics::Value simTicks;
        statistics::Value finalTick;
        statistics::Value simFreq;
        statistics::Value hostSeconds;

        statistics::Formula hostTickRate;
        statistics::Value hostMemory;

        static RootStats instance;

      private:
        RootStats();

        RootStats(const RootStats &) = delete;
        RootStats &operator=(const RootStats &) = delete;

        Time statTime;
        Tick startTick;
    };

  public:

    /// Check whether time syncing is enabled.
    bool timeSyncEnabled() const { return _enabled; }
    /// Retrieve the period for the sync event.
    const Time timeSyncPeriod() const { return _period; }
    /// Retrieve the threshold for time remaining to spin wait.
    const Time timeSyncSpinThreshold() const { return _spinThreshold; }

    /// Enable or disable time syncing.
    void timeSyncEnable(bool en);
    /// Configure the period for time sync events.
    void timeSyncPeriod(Time newPeriod);
    /// Set the threshold for time remaining to spin wait.
    void timeSyncSpinThreshold(Time newThreshold);

    PARAMS(Root);

    // The int parameter is ignored, it's just so we can define a custom
    // create() method.
    Root(const Params &p, int);

    /** Schedule the timesync event at startup().
     */
    void startup() override;

    void serialize(CheckpointOut &cp) const override;
    void unserialize(CheckpointIn &cp) override;
};

/**
 * Global simulator statistics that are not associated with a
 * specific SimObject.
 */
extern Root::RootStats &rootStats;

} // namespace gem5

#endif // __SIM_ROOT_HH__