HDFDirector
ptolemy.domains.hdf.kernel.HDFDirector

The Heterochronous Dataflow (HDF) domain is an extension of the Synchronous Dataflow (SDF) domain and implements the HDF model of computation [1]. In SDF, the set of port rates (called rate signatures) of an actor are constant. In HDF, however, rate signatures are allowed to change between iterations of the HDF schedule. <p> This director is often used with HDFFSMDirector. The HDFFSMDirector governs the execution of a modal model. The change of rate signatures can be modeled by state transitions of the modal model, in which each state refinement infers a set of rate signatures. Within each state, the HDF model behaves like an SDF model. <p> This director recomputes the schedules dynamically. To improve efficiency, this director uses a CachedSDFScheduler. A CachedSDFScheduler caches schedules labeled by their corresponding rate signatures, with the most recently used at the beginning of the queue. Therefore, when a state in HDF is revisited, the schedule identified by its rate signatures in the cache is used. We do not need to recompute the schedule. <p> The size of the cache in the CachedSDFScheduler is set by the <i>scheduleCacheSize</i> parameter of HDFDirector. The default value of this parameter is 100. If the cache is full, the least recently used schedule (at the end of the cache) is discarded. <p> <b>References</b> <p> <OL> <LI> A. Girault, B. Lee, and E. A. Lee, ``<A HREF="http://ptolemy.eecs.berkeley.edu/papers/98/starcharts"> Hierarchical Finite State Machines with Multiple Concurrency Models</A>, '' April 13, 1998.</LI> </ol>

Author(s): Ye Zhou. Contributor: Brian K. Vogel
Version:$Id: HDFDirector.doc.html,v 1.1 2006/02/22 18:40:27 mangal Exp $
Pt.Proposed Rating:Red (zhouye)
Pt.Accepted Rating:Red (cxh)




scheduleCacheSize
A parameter representing the size of the schedule cache to use. If the value is less than or equal to zero, then schedules will never be discarded from the cache. The default value is 100. <p> Note that the number of schedules in an HDF model can be exponential in the number of actors. Setting the cache size to a very large value is therefore not recommended if the model contains a large number of HDF actors.