ptolemy.domains.fsm.kernel
Class FSMCausalityInterface

java.lang.Object
  ptolemy.actor.util.DefaultCausalityInterface
      ptolemy.actor.util.CausalityInterfaceForComposites
          ptolemy.domains.fsm.kernel.FSMCausalityInterface

All Implemented Interfaces:

CausalityInterface

public class FSMCausalityInterface
extends CausalityInterfaceForComposites

This class infers the causality interface of an FSMActor by checking the guards and actions of the transitions. If any transition in the model has an output action that writes to a port and a guard that references an input port, then there is a direct dependency of that output on that input. Otherwise, there is no dependency. Note that this is a conservative analysis in that it may indicate a dependency when there is none. For example, if all outgoing transitions from a state produce the same output value, and a transition is always taken, then irrespective of the guards, the output has no dependency on the inputs. A precise analysis, however, is much more difficult (probably undecidable).

All input ports that affect the state (i.e. that are mentioned in any guard) must be in an equivalence class. Otherwise, we cannot reliably make a decision about what the next state is. In addition, if any input in a refinement affects an output, that input must also be in this equivalence class. Otherwise, the scheduler will assume there is no relationship between these inputs and could provide an event that triggers a state transition in an earlier firing than an event that triggers an output from the current refinement.

Since:

Ptolemy II 8.0

Version:

$Id: FSMCausalityInterface.java 57044 2010-01-27 22:41:05Z cxh $

Author:

Edward A. Lee

Accepted Rating:

Red (eal)

Proposed Rating:

Yellow (eal)

Field Summary

Fields inherited from class ptolemy.actor.util.CausalityInterfaceForComposites

_actorDepthVersion, _actorToDepth, _dependencyVersion, _equivalenceClasses, _forwardDependencies, _reverseDependencies

Fields inherited from class ptolemy.actor.util.DefaultCausalityInterface

_actor, _backwardPrunedDependencies, _defaultDependency, _delayDependencies, _EMPTY_COLLECTION, _forwardPrunedDependencies

Constructor Summary

FSMCausalityInterface(Actor actor, Dependency defaultDependency)
Construct a causality interface for the specified actor.

Method Summary

Dependency

getDependency(IOPort input, IOPort output) Return the dependency between the specified input port and the specified output port.

Methods inherited from class ptolemy.actor.util.CausalityInterfaceForComposites

_computeActorDepth, checkForCycles, dependentPorts, describeDepths, equivalentPorts, getDepthOfActor, getDepthOfPort, invalidate, removeDependency, topologicalSort

Methods inherited from class ptolemy.actor.util.DefaultCausalityInterface

_growDependencies, declareDelayDependency, getActor, getDefaultDependency, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

FSMCausalityInterface

public FSMCausalityInterface(Actor actor,
                             Dependency defaultDependency)
                      throws java.lang.IllegalArgumentException

Construct a causality interface for the specified actor.

Parameters:

actor - The actor for which this is a causality interface. This is required to be an instance of CompositeEntity.

defaultDependency - The default dependency of an output port on an input port.

Throws:

java.lang.IllegalArgumentException - If the actor parameter is not an instance of CompositeEntity.

Method Detail

getDependency

public Dependency getDependency(IOPort input,
                                IOPort output)
                         throws IllegalActionException

Return the dependency between the specified input port and the specified output port. This is done by checking the guards and actions of all the transitions. When called for the first time since a change in the model structure, this method performs the complete analysis of the FSM and caches the result. Subsequent calls just look up the result.

Specified by:

getDependency in interface CausalityInterface

Overrides:

getDependency in class CausalityInterfaceForComposites

Parameters:

input - The input port.

output - The output port, or null to update the dependencies (and record equivalence classes) without requiring there to be an output port.

Returns:

The dependency between the specified input port and the specified output port, or null if a null output is port specified.

Throws:

IllegalActionException - If a guard expression cannot be parsed.