PTOLEMY II - CiteSeerX

Designing Actors
be used in domains with fixed-point semantics, such as SR.
When using a PortParameter in an actor, care must be exercised to call update() exactly once per
firing prior to calling getToken(). Each time update() is called, a new token will be consumed from the
associated port (if the port is connected and has a token). If this is called multiple times in an iteration,
it may result in consuming tokens that were intended for subsequent iterations. Thus, for example,
update() should not be called in fire() and then again in postfire(). Moreover, in some domains (such
public class Ramp extends SequenceSource {
}
}
public Ramp(CompositeEntity container, String name)
throws NameDuplicationException, IllegalActionException {
super(container, name);
init = new Parameter(this, "init");
init.setExpression("0");
step = new PortParameter(this, "step");
step.setExpression("1");
// set the type constraints.
output.setTypeAtLeast(init);
output.setTypeAtLeast(step);
public Parameter init;
public PortParameter step;
public void attributeChanged(Attribute attribute) throws IllegalActionException {
if (attribute == init) {
_stateToken = init.getToken();
} else {
super.attributeChanged(attribute);
}
}
public Object clone(Workspace workspace) throws CloneNotSupportedException {
Ramp newObject = (Ramp)super.clone(workspace);
newObject.output.setTypeAtLeast(newObject.init);
newObject.output.setTypeAtLeast(newObject.step);
...
return newObject;
}
public void fire() throws IllegalActionException {
super.fire();
output.send(0, _stateToken);
}
public void initialize() throws IllegalActionException {
super.initialize();
_stateToken = init.getToken();
}
...
public boolean postfire() throws IllegalActionException {
step.update();
_stateToken = _stateToken.add(step.getToken());
return super.postfire();
}
private Token _stateToken = null;
FIGURE 5.10. Code segments from the Ramp actor.
Heterogeneous Concurrent Modeling and Design 169