code: /**
   * Copyright (c) 2004-2005, Regents of the University of California
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * Redistributions of source code must retain the above copyright notice,
   * this list of conditions and the following disclaimer.
   *
   * 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.
   *
   * Neither the name of the University of California, Los Angeles 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 COPYRIGHT HOLDERS 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 COPYRIGHT
   * OWNER 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.
   */
  
  package avrora.sim.clock;
  
  import avrora.sim.Simulator;
  
  /**
   * The <code>ClockPrescaler</code> class represents a clock that is another clock scaled appropriately; e.g.
   * 8x slower.
   *
   * @author Ben L. Titzer
   */
  public class ClockPrescaler extends Clock {
  
      /**
       * The <code>driveClock</code> field stores a reference to the clock that the prescaler is derived from.
       */
      protected final Clock driveClock;
  
      /**
       * The <code>divider</code> stores the number of cycles of the underlying clock are equivalent to one
       * cycle of this clock. For example, with a divider or 8, the underlying clock ticks 8 times for each tick
       * of this clock.
       */
      protected final int divider;
  
      /**
       * The <code>base</code> field stores the cycle count of the underlying clock at the last time that this
       * clock was reset.
       */
      protected long base;
  
      /**
       * The <code>ticksBeforeBase</code> field stores the number of ticks that were recorded before the
       * prescaler was reset. This is used in the calculation of the total number of ticks that have elapsed.
       */
      protected long ticksBeforeBase;
  
      /**
       * The constructor of the <code>ClockPrescaler</code> creates a new clock that is an integer multiple
       * slower than the clock that it is derived from. Additionally, the phase at which this clock fires can be
       * adjusted by resetting.
       *
       * @param n       the name of the new clock
       * @param drive   the clock that drives this derived clock
       * @param divider the muliple by which the derived clock is slower than the source
       */
      public ClockPrescaler(String n, Clock drive, int divider) {
          super(n, drive.getHZ() / divider);
          driveClock = drive;
          this.divider = divider;
      }
  
      /**
       * The <code>getCount()</code> method returns the number of clock cycles (ticks) that have elapsed for
       * this clock. In the implementation of the <code>ClockPrescaler</code>, this method calculates the number
       * of scaled cycles since the last reset.
       *
       * @return the number of elapsed time ticks in clock cycles
       */
      public long getCount() {
          return (driveClock.getCount() - base) / divider;
      }
  
      /**
       * The <code>getTotalCount()</code> method returns the total number of clock cycles (ticks) that have
       * elapsed for this clock. In the implementation of the <code>ClockPrescaler</code>, this method
       * calculates the number of scaled cycles since the last reset, plus the number of ticks elapsed before
       * the reset.
       *
       * @return the number of elapsed time ticks in clock cycles
       */
      public long getTotalCount() {
          return getCount() + ticksBeforeBase;
      }
  
      /**
       * The <code>insertEvent()</code> method inserts an event into the event queue of the clock with the
       * specified delay in clock cycles. The event will then be executed at the future time specified. In the
       * implementation of <code>ClockPrescaler</code>, the event will be scheduled in the underlying clock,
       * with the delay calculated correctly from the last time that the prescaler was reset.
       *
       * @param e     the event to be inserted
       * @param delta the number of (scaled) cycles in the future at which to fire
       */
      public void insertEvent(Simulator.Event e, long delta) {
          long driverCount = driveClock.getCount() - base;
          long nextTick = ((driverCount / divider) + 1) * divider;
          driveClock.insertEvent(e, nextTick - driverCount);
      }
  
      /**
       * The <code>removeEvent()</code> method removes an event from the event queue of the clock. The
       * comparison used is reference equality, not <code>.equals()</code>.
       *
       * @param e the event to remove
       */
      public void removeEvent(Simulator.Event e) {
          driveClock.removeEvent(e);
      }
  
      /**
       * The <code>reset()</code> method resets the internal clock prescaler to zero. Thus, the prescaler's
       * previous phase is broken, and the clock signal continues with the same frequency, only that the first
       * tick will happen <code>divider</code> cycles from now.
       */
      public void reset() {
          long newbase = driveClock.getCount();
          long diff = newbase - base;
          ticksBeforeBase += diff / divider;
          base = newbase;
      }
  
  }
  