/* A nonstrict actor that delays tokens by one iteration.
Copyright (c) 1997-2007 The Regents of the University of California.
All rights reserved.
Permission is hereby granted, without written agreement and without
license or royalty fees, to use, copy, modify, and distribute this
software and its documentation for any purpose, provided that the above
copyright notice and the following two paragraphs appear in all copies
of this software.
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
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THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE
PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF
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ENHANCEMENTS, OR MODIFICATIONS.
PT_COPYRIGHT_VERSION_2
COPYRIGHTENDKEY
*/
package ptolemy.domains.sr.lib;
import java.util.List;
import ptolemy.actor.lib.Transformer;
import ptolemy.data.Token;
import ptolemy.data.expr.Parameter;
import ptolemy.graph.Inequality;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.InternalErrorException;
import ptolemy.kernel.util.NameDuplicationException;
//////////////////////////////////////////////////////////////////////////
//// NonstrictDelay
/**
This actor provides a one-tick delay. On each firing, it produces
on the output port whatever value it read on the input port in the
previous tick of the clock. If the input was absent on the previous
tick of the clock, then the output will be absent. On the first tick,
the output is <i>initialValue</i> if it is given, and absent otherwise.
In contrast to the Pre actor, this actor is non-strict, and hence can
break causality loops. Whereas Pre provides a one-step delay of
non-absent values, this actor simply delays by one clock tick.
@see Pre
@see ptolemy.domains.sdf.lib.SampleDelay
@see ptolemy.domains.de.lib.TimedDelay
@author Paul Whitaker, Elaine Cheong, and Edward A. Lee
@version $Id: NonStrictDelay.java,v 1.45 2007/12/07 06:26:57 cxh Exp $
@since Ptolemy II 2.0
@Pt.ProposedRating Yellow (celaine)
@Pt.AcceptedRating Yellow (cxh)
*/
public class NonStrictDelay extends Transformer {
/** Construct an actor in the specified container with the specified
* name.
* @param container The container.
* @param name The name of this actor within the container.
* @exception IllegalActionException If the actor cannot be contained
* by the proposed container.
* @exception NameDuplicationException If the name coincides with
* an actor already in the container.
*/
public NonStrictDelay(CompositeEntity container, String name)
throws IllegalActionException, NameDuplicationException {
super(container, name);
initialValue = new Parameter(this, "initialValue");
}
///////////////////////////////////////////////////////////////////
//// ports and parameters ////
/** Initial token value. Can be of any type.
* @see #typeConstraintList()
*/
public Parameter initialValue;
///////////////////////////////////////////////////////////////////
//// public methods ////
/** If the input known and there is a token on the input port,
* consume the token from the input port, and store it for output
* on the next iteration. Otherwise, store an AbsentToken for
* output on the next iteration.
* If a token was received on the previous iteration, output it to the
* receivers. Otherwise, notify the receivers that there will never be
* any token available in the current iteration.
* @exception IllegalActionException If there is no director.
*/
public void fire() throws IllegalActionException {
super.fire();
if (_previousToken != null) {
if (_previousToken == AbsentToken.ABSENT) {
output.sendClear(0);
} else {
output.send(0, _previousToken);
}
} else {
output.sendClear(0);
}
}
/** Initialize the state of the actor.
* @exception IllegalActionException If there is no director.
*/
public void initialize() throws IllegalActionException {
// Note that this will default to null if there is no initialValue set.
_previousToken = initialValue.getToken();
super.initialize();
}
/** Return false. This actor can produce some output event the input
* receiver has status unknown.
*
* @return False.
*/
public boolean isStrict() {
return false;
}
/** Update the state of the actor.
* @exception IllegalActionException If there is no director.
*/
public boolean postfire() throws IllegalActionException {
if (input.isKnown(0)) {
if (input.hasToken(0)) {
_previousToken = input.get(0);
} else {
_previousToken = AbsentToken.ABSENT;
}
}
return super.postfire();
}
/** Override the base class to declare that the <i>output</i>
* does not depend on the <i>input</i> in a firing.
*/
public void pruneDependencies() {
super.pruneDependencies();
removeDependency(input, output);
}
/** Override the method in the base class so that the type
* constraint for the <i>initialValue</i> parameter will be set
* if it contains a value.
* @return a list of Inequality objects.
* @see ptolemy.graph.Inequality
*/
public List typeConstraintList() {
List typeConstraints = super.typeConstraintList();
try {
if (initialValue.getToken() != null) {
Inequality ineq = new Inequality(initialValue.getTypeTerm(),
output.getTypeTerm());
typeConstraints.add(ineq);
}
} catch (IllegalActionException ex) {
// Errors in the initialValue parameter should already
// have been caught in getAttribute() method of the base
// class.
throw new InternalErrorException("Bad initialValue value!");
}
return typeConstraints;
}
///////////////////////////////////////////////////////////////////
//// protected variables ////
/** The token received on the previous iteration to be output on the
* current iteration.
*/
protected Token _previousToken;
}