001/* An actor that delays the input by the specified amount.
002
003 Copyright (c) 1998-2015 The Regents of the University of California.
004 All rights reserved.
005 Permission is hereby granted, without written agreement and without
006 license or royalty fees, to use, copy, modify, and distribute this
007 software and its documentation for any purpose, provided that the above
008 copyright notice and the following two paragraphs appear in all copies
009 of this software.
010
011 IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
012 FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
013 ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
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018 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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024 PT_COPYRIGHT_VERSION_2
025 COPYRIGHTENDKEY
026
027 */
028package ptolemy.actor.lib;
029
030import ptolemy.actor.Director;
031import ptolemy.actor.SuperdenseTimeDirector;
032import ptolemy.data.Token;
033import ptolemy.kernel.CompositeEntity;
034import ptolemy.kernel.util.IllegalActionException;
035import ptolemy.kernel.util.NameDuplicationException;
036import ptolemy.kernel.util.Workspace;
037
038///////////////////////////////////////////////////////////////////
039//// MicrostepDelay
040
041/**
042 This actor delays the input by one microstep. The output is always
043 absent in the first firing. This actor is designed
044 to be used in domains where the director implements
045 SuperdenseTimeDirector, like Continuous and DE.
046 Inputs are read only during the postfire() method.
047 If an input is present, then this actor schedules itself to fire again
048 to produce the just received token on the corresponding output channel in
049 the next microstep at the same time stamp.
050 <p>
051 When this actor is used in the Continuous domain, it requires that its
052 input be purely  discrete (specifically that it be absent at microstep 0).
053 The reason for rejecting continuous inputs is that a continuous input
054 would cause a stuttering Zeno condition, where time cannot advance.
055
056 @author Edward A. Lee
057 @version $Id$
058 @since Ptolemy II 10.0
059 @Pt.ProposedRating Yellow (eal)
060 @Pt.AcceptedRating Red (eal)
061 */
062public class MicrostepDelay extends Transformer {
063    /** Construct an actor with the specified container and name.
064     *  Constrain that the output type to be the same as the input type.
065     *  @param container The composite entity to contain this one.
066     *  @param name The name of this actor.
067     *  @exception IllegalActionException If the entity cannot be contained
068     *   by the proposed container.
069     *  @exception NameDuplicationException If the container already has an
070     *   actor with this name.
071     */
072    public MicrostepDelay(CompositeEntity container, String name)
073            throws NameDuplicationException, IllegalActionException {
074        super(container, name);
075
076        output.setTypeSameAs(input);
077    }
078
079    ///////////////////////////////////////////////////////////////////
080    ////                         public methods                    ////
081
082    /** Clone the actor into the specified workspace. Set a type
083     *  constraint that the output type is the same as the that of input.
084     *  @param workspace The workspace for the new object.
085     *  @return A new actor.
086     *  @exception CloneNotSupportedException If a derived class has
087     *   has an attribute that cannot be cloned.
088     */
089    @Override
090    public Object clone(Workspace workspace) throws CloneNotSupportedException {
091        MicrostepDelay newObject = (MicrostepDelay) super.clone(workspace);
092        newObject.output.setTypeSameAs(newObject.input);
093        return newObject;
094    }
095
096    /** Declare that the output does not depend on the input in a firing.
097     *  @exception IllegalActionException If the causality interface
098     *  cannot be computed.
099     *  @see #getCausalityInterface()
100     */
101    @Override
102    public void declareDelayDependency() throws IllegalActionException {
103        _declareDelayDependency(input, output, 0.0);
104    }
105
106    /** Read one token from the input. Send out a token that is scheduled
107     *  to be produced at the current time.
108     *  @exception IllegalActionException If there is no director, or the
109     *  input can not be read, or the output can not be sent.
110     */
111    @Override
112    public void fire() throws IllegalActionException {
113        super.fire();
114        if (_pendingOutput != null) {
115            output.send(0, _pendingOutput);
116            if (_debugging) {
117                _debug("Sending output. Value = " + _pendingOutput);
118            }
119        } else {
120            // Nothing to send. Assert the output to be absent.
121            output.send(0, null);
122            if (_debugging) {
123                _debug("Nothing to send. Asserting absent output at time "
124                        + getDirector().getModelTime());
125            }
126        }
127    }
128
129    /** Initialize the states of this actor.
130     *  @exception IllegalActionException If the director does
131     *   not implement SuperdenseTimeDirector.
132     */
133    @Override
134    public void initialize() throws IllegalActionException {
135        super.initialize();
136        _pendingOutput = null;
137
138        if (!(getDirector() instanceof SuperdenseTimeDirector)) {
139            throw new IllegalActionException(this,
140                    "MicrostepDelay can only be used with a director that implements "
141                            + "SuperdenseTimeDirector, such as ContinuousDirector or DEDirector.");
142        }
143    }
144
145    /** Return false indicating that this actor can be fired even if
146     *  the inputs are unknown.
147     *  @return False.
148     */
149    @Override
150    public boolean isStrict() {
151        return false;
152    }
153
154    /** Read the input, if there is one, and request refiring.
155     *  @exception IllegalActionException If scheduling to refire cannot
156     *  be performed, or if there is input and the current microstep is
157     *  zero, or if the superclass throws it.
158     */
159    @Override
160    public boolean postfire() throws IllegalActionException {
161        // No point in using the isTime() method here, since we need
162        // all the intermediate values.
163        Director director = getDirector();
164        if (input.hasToken(0)) {
165            /* Do not enforce this. It is useful sometimes.
166            int microstep = ((SuperdenseTimeDirector) director).getIndex();
167            if (microstep == 0) {
168                throw new IllegalActionException(this,
169                        "Input is not purely discrete.");
170            }
171             */
172            _pendingOutput = input.get(0);
173            // Do not use fireAtCurrentTime() because if synchronizeToRealTime is set,
174            // that will not necessarily match the current model time.
175            director.fireAt(this, director.getModelTime());
176            if (_debugging) {
177                _debug("Read input with value = " + _pendingOutput);
178            }
179        } else {
180            _pendingOutput = null;
181        }
182        return super.postfire();
183    }
184
185    ///////////////////////////////////////////////////////////////////
186    ////                         protected variables               ////
187
188    /** A token to send in the next microstep. */
189    protected Token _pendingOutput;
190}