src/sim/clocked_object.hh

   1 /*
   2  * Copyright (c) 2012-2013 ARM Limited
   3  * Copyright (c) 2013 Cornell University
   4  * All rights reserved
   5  *
   6  * The license below extends only to copyright in the software and shall
   7  * not be construed as granting a license to any other intellectual
   8  * property including but not limited to intellectual property relating
   9  * to a hardware implementation of the functionality of the software
  10  * licensed hereunder.  You may use the software subject to the license
  11  * terms below provided that you ensure that this notice is replicated
  12  * unmodified and in its entirety in all distributions of the software,
  13  * modified or unmodified, in source code or in binary form.
  14  *
  15  * Redistribution and use in source and binary forms, with or without
  16  * modification, are permitted provided that the following conditions are
  17  * met: redistributions of source code must retain the above copyright
  18  * notice, this list of conditions and the following disclaimer;
  19  * redistributions in binary form must reproduce the above copyright
  20  * notice, this list of conditions and the following disclaimer in the
  21  * documentation and/or other materials provided with the distribution;
  22  * neither the name of the copyright holders nor the names of its
  23  * contributors may be used to endorse or promote products derived from
  24  * this software without specific prior written permission.
  25  *
  26  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  27  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  28  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  29  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  30  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  31  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  32  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  33  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  34  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  35  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  36  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  37  *
  38  * Authors: Andreas Hansson
  39  *          Christopher Torng
  40  */
  41
  42 /**
  43  * @file
  44  * ClockedObject declaration and implementation.
  45  */
  46
  47 #ifndef __SIM_CLOCKED_OBJECT_HH__
  48 #define __SIM_CLOCKED_OBJECT_HH__
  49
  50 #include "base/intmath.hh"
  51 #include "base/misc.hh"
  52 #include "params/ClockedObject.hh"
  53 #include "sim/core.hh"
  54 #include "sim/clock_domain.hh"
  55 #include "sim/sim_object.hh"
  56
  57 /**
  58  * The ClockedObject class extends the SimObject with a clock and
  59  * accessor functions to relate ticks to the cycles of the object.
  60  */
  61 class ClockedObject : public SimObject
  62 {
  63
  64   private:
  65
  66     // the tick value of the next clock edge (>= curTick()) at the
  67     // time of the last call to update()
  68     mutable Tick tick;
  69
  70     // The cycle counter value corresponding to the current value of
  71     // 'tick'
  72     mutable Cycles cycle;
  73
  74     /**
  75      * Prevent inadvertent use of the copy constructor and assignment
  76      * operator by making them private.
  77      */
  78     ClockedObject(ClockedObject&);
  79     ClockedObject& operator=(ClockedObject&);
  80
  81     /**
  82      *  Align cycle and tick to the next clock edge if not already done. When
  83      *  complete, tick must be at least curTick().
  84      */
  85     void update() const
  86     {
  87         // both tick and cycle are up-to-date and we are done, note
  88         // that the >= is important as it captures cases where tick
  89         // has already passed curTick()
  90         if (tick >= curTick())
  91             return;
  92
  93         // optimise for the common case and see if the tick should be
  94         // advanced by a single clock period
  95         tick += clockPeriod();
  96         ++cycle;
  97
  98         // see if we are done at this point
  99         if (tick >= curTick())
 100             return;
 101
 102         // if not, we have to recalculate the cycle and tick, we
 103         // perform the calculations in terms of relative cycles to
 104         // allow changes to the clock period in the future
 105         Cycles elapsedCycles(divCeil(curTick() - tick, clockPeriod()));
 106         cycle += elapsedCycles;
 107         tick += elapsedCycles * clockPeriod();
 108     }
 109
 110     /**
 111      * The clock domain this clocked object belongs to
 112      */
 113     ClockDomain &clockDomain;
 114
 115   protected:
 116
 117     /**
 118      * Create a clocked object and set the clock domain based on the
 119      * parameters.
 120      */
 121     ClockedObject(const ClockedObjectParams* p) :
 122         SimObject(p), tick(0), cycle(0), clockDomain(*p->clk_domain)
 123     {
 124         // Register with the clock domain, so that if the clock domain
 125         // frequency changes, we can update this object's tick.
 126         clockDomain.registerWithClockDomain(this);
 127     }
 128
 129     /**
 130      * Virtual destructor due to inheritance.
 131      */
 132     virtual ~ClockedObject() { }
 133
 134     /**
 135      * Reset the object's clock using the current global tick value. Likely
 136      * to be used only when the global clock is reset. Currently, this done
 137      * only when Ruby is done warming up the memory system.
 138      */
 139     void resetClock() const
 140     {
 141         Cycles elapsedCycles(divCeil(curTick(), clockPeriod()));
 142         cycle = elapsedCycles;
 143         tick = elapsedCycles * clockPeriod();
 144     }
 145
 146   public:
 147
 148     /**
 149      * Update the tick to the current tick.
 150      *
 151      */
 152     inline void updateClockPeriod() const
 153     {
 154         update();
 155     }
 156
 157     /**
 158      * Determine the tick when a cycle begins, by default the current one, but
 159      * the argument also enables the caller to determine a future cycle. When
 160      * curTick() is on a clock edge, the number of cycles in the parameter is
 161      * added to curTick() to be returned. When curTick() is not aligned to a
 162      * clock edge, the number of cycles in the parameter is added to the next
 163      * clock edge.
 164      *
 165      * @param cycles The number of cycles into the future
 166      *
 167      * @return The start tick when the requested clock edge occurs. Precisely,
 168      * this tick can be
 169      *     curTick() + [0, clockPeriod()) + clockPeriod() * cycles
 170      */
 171     inline Tick clockEdge(Cycles cycles = Cycles(0)) const
 172     {
 173         // align tick to the next clock edge
 174         update();
 175
 176         // figure out when this future cycle is
 177         return tick + clockPeriod() * cycles;
 178     }
 179
 180     /**
 181      * Determine the current cycle, corresponding to a tick aligned to
 182      * a clock edge.
 183      *
 184      * @return When curTick() is on a clock edge, return the Cycle corresponding
 185      * to that clock edge. When curTick() is not on a clock edge, return the
 186      * Cycle corresponding to the next clock edge.
 187      */
 188     inline Cycles curCycle() const
 189     {
 190         // align cycle to the next clock edge.
 191         update();
 192
 193         return cycle;
 194     }
 195
 196     /**
 197      * Based on the clock of the object, determine the start tick of the first
 198      * cycle that is at least one cycle in the future. When curTick() is at the
 199      * current cycle edge, this returns the next clock edge. When calling this
 200      * during the middle of a cycle, this returns 2 clock edges in the future.
 201      *
 202      * @return The start tick of the first cycle that is at least one cycle in
 203      * the future. Precisely, the returned tick can be in the range
 204      *     curTick() + [clockPeriod(), 2 * clockPeriod())
 205      */
 206     Tick nextCycle() const
 207     { return clockEdge(Cycles(1)); }
 208
 209     inline uint64_t frequency() const
 210     {
 211         return SimClock::Frequency / clockPeriod();
 212     }
 213
 214     inline Tick clockPeriod() const
 215     {
 216         return clockDomain.clockPeriod();
 217     }
 218
 219     inline Cycles ticksToCycles(Tick t) const
 220     { return Cycles(divCeil(t, clockPeriod())); }
 221
 222 };
 223
 224 #endif //__SIM_CLOCKED_OBJECT_HH__