xref: /gem5/src/systemc/ext/tlm_utils/tlm_quantumkeeper.h

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#ifndef __SYSTEMC_EXT_TLM_UTILS_TLM_QUANTUMKEEPER_H__
#define __SYSTEMC_EXT_TLM_UTILS_TLM_QUANTUMKEEPER_H__

#include "../core/sc_time.hh"

namespace tlm_utils
{

// tlm_quantumkeeper class
//
// The tlm_quantumkeeper class is used to keep track of the local time in
// an initiator (how much it has run ahead of the SystemC time), to
// synchronize with SystemC time etc.
class tlm_quantumkeeper
{
  public:
    //
    // Static setters/getters for the global quantum value.
    //
    // The global quantum is the maximum time an initiator can run ahead of
    // SystemC time. All initiators will synchronize on timing points that are
    // multiples of the global quantum value.
    //
    static void
    set_global_quantum(const sc_core::sc_time &t)
    {
        tlm::tlm_global_quantum::instance().set(t);
    }

    static const sc_core::sc_time &
    get_global_quantum()
    {
        return tlm::tlm_global_quantum::instance().get();
    }

  public:
    tlm_quantumkeeper() : m_next_sync_point(sc_core::SC_ZERO_TIME),
                          m_local_time(sc_core::SC_ZERO_TIME)
    {}

    virtual ~tlm_quantumkeeper() {}

    // Increment the local time (the time the initiator is ahead of the
    // systemC time) After incrementing the local time an initiator should
    // check (with the need_sync method) if a sync is required.
    virtual void inc(const sc_core::sc_time &t) { m_local_time += t; }

    // Sets the local time (the time the initiator is ahead of the
    // systemC time) After changing the local time an initiator should
    // check (with the need_sync method) if a sync is required.
    virtual void set(const sc_core::sc_time &t) { m_local_time = t; }

    // Checks if a sync to systemC is required for this initiator. This will
    // be the case if the local time becomes greater than the local (current)
    // quantum value for this initiator.
    virtual bool
    need_sync() const
    {
        return sc_core::sc_time_stamp() + m_local_time >= m_next_sync_point;
    }

    // Synchronize to systemC. This call will do a wait for the time the
    // initiator was running ahead of systemC time and reset the
    // tlm_quantumkeeper.
    virtual void
    sync()
    {
        sc_core::wait(m_local_time);
        reset();
    }

    // Non-virtual convenience method to set the local time and sync only if
    // needed
    void
    set_and_sync(const sc_core::sc_time &t)
    {
        set(t);
        if (need_sync())
            sync();
    }

    // Resets the local time to SC_ZERO_TIME and computes the value of the
    // next local quantum. This method should be called by an initiator after
    // a wait because of a synchronization request by a target (TLM_ACCEPTED,
    // or TLM_UPDATED).
    virtual void
    reset()
    {
        m_local_time = sc_core::SC_ZERO_TIME;
        m_next_sync_point = sc_core::sc_time_stamp() + compute_local_quantum();
    }

    // Helper function to get the current systemC time, taken the local time
    // into account. The current systemC time is calculated as the time
    // returned by sc_time_stamp incremeneted with the time the initiator is
    // running ahead.
    virtual sc_core::sc_time
    get_current_time() const
    {
        return sc_core::sc_time_stamp() + m_local_time;
    }

    // Helper functions to get the time the initiator is running ahead of
    // systenC (local time). This time should be passed to a target in the
    // nb_transport call
    virtual sc_core::sc_time
    get_local_time() const
    {
        return m_local_time;
    }

  protected:
    // Calculate the next local quantum for this initiator.
    //
    // The method can be overloaded in a derived object if an initiator wants
    // to use another local quantum. This derived object should also take the
    // global quantum into account. It's local quantum should not be set to a
    // value that is larger than the quantum returned by the
    // compute_local_quantum of the tlm_global_quantum singleton.
    virtual sc_core::sc_time
    compute_local_quantum()
    {
        return tlm::tlm_global_quantum::instance().compute_local_quantum();
    }

  protected:
    sc_core::sc_time m_next_sync_point;
    sc_core::sc_time m_local_time;
};

} // namespace tlm_utils

#endif /* __SYSTEMC_EXT_TLM_UTILS_TLM_QUANTUMKEEPER_H__ */