/* A register with one trigger port that accepts read requests.
Copyright (c) 2004-2006 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
SUCH DAMAGE.
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
CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
ENHANCEMENTS, OR MODIFICATIONS.
PT_COPYRIGHT_VERSION_2
COPYRIGHTENDKEY
*/
package ptolemy.actor.lib.vhdl;
import ptolemy.actor.TypedIOPort;
import ptolemy.data.type.BaseType;
import ptolemy.kernel.CompositeEntity;
import ptolemy.kernel.util.IllegalActionException;
import ptolemy.kernel.util.NameDuplicationException;
//////////////////////////////////////////////////////////////////////////
//// Register
/**
A register is a stateful actor with a trigger port that accepts
read requests.
<p>
In the fire() method, if there is an event on the <i>trigger</i>
input port, this actor will produce an output event. The value
of the output event will be the previously recorded event
from the <i>input</i> port, or the value of the <i>initialValue</i>
parameter if there has been no previous input event. If, however,
<i>initialValue</i> contains no value, then no output will be
produced. In the postfire() method, if there is an input event on
the <i>input</i> port, then its value is recorded to be used
in future firings as the value of the output.
<p>
The inputs can be of any token type, but the <i>output</i> port
is constrained to be of a type at least that of the <i>input</i>
port and the <i>initialValue</i> parameter.
<p>
This class extends Sampler. Unlike its base class, this actor
can be used to break dependencies in a feedback loop in that
the input tokens are consumed from the input ports after the outputs
are generated. Another difference is that the Register actor can be
fired when either the trigger port or the input port has a token, while
the Sampler can only be fired when the trigger port receives a token.
<p>
Both the <i>input</i> port and the <i>output</i> port are multiports.
Generally, their widths should match. Otherwise, if the width of the
<i>input</i> is greater than the width of the <i>output</i>, the extra
input tokens will not appear on any output, although they will be
consumed from the input port. If the width of the <i>output</i> is
greater than that of the <i>input</i>, then the last few channels of
the <i>output</i> will never emit tokens.
<p>
Note: If the width of the input changes during execution, then the
most recent inputs are forgotten, as if the execution of the model
were starting over.
@author Edward A. Lee, Haiyang Zheng
@version $Id$
@since Ptolemy II 4.1
@Pt.ProposedRating Yellow (eal)
@Pt.AcceptedRating Red (eal)
@see ptolemy.domains.de.lib.Sampler
*/
public class Register extends SynchronousFixTransformer {
/** Construct an actor with the given container and name.
* @param container The container.
* @param name The name of this actor.
* @exception IllegalActionException If the actor cannot be contained
* by the proposed container.
* @exception NameDuplicationException If the container already has an
* actor with this name.
*/
public Register(CompositeEntity container, String name)
throws NameDuplicationException, IllegalActionException {
super(container, name);
input = new TypedIOPort(this, "input", true, false);
input.setTypeEquals(BaseType.FIX);
}
///////////////////////////////////////////////////////////////////
//// public methods ////
/** If there is a token in the <i>trigger</i> port, emit the previously
* seen inputs from the <i>input</i> port. If there has been no
* previous input tokens, but the <i>initialValue</i> parameter
* has been set, emit the value of the <i>initialValue</i> parameter.
* Otherwise, emit nothing.
* @exception IllegalActionException If there is no director.
*/
public void fire() throws IllegalActionException {
if (input.hasToken(0)) {
sendOutput(output, 0, input.get(0));
}
}
/** Override the base class to declare that the <i>input</i> and
* port does not depend on the <i>output</i> in a firing.
*/
public void preinitialize() throws IllegalActionException {
super.preinitialize();
removeDependency(input, output);
}
/** Input for tokens to be added. This is a multiport of fix point
* type
*/
public TypedIOPort input;
}