
PSDFScheduler |
ptolemy.domains.psdf.kernel.PSDFScheduler |
A scheduler that implements basic scheduling of PSDF graphs. PSDF
scheduling is similar to SDF scheduling, EXCEPT:
<p> 1) Because parameter values may change, the solution to the
balance equation is computed symbolically. i.e. the repetitions
vector is a function of the parameter values.
<p> 2) Because the firing vector may change, the schedule determined
by this class can only be a quasi-static, or parameterized schedule.
Note that parameterized schedules cannot generally be constructed for
models with feedback or with unconstrained parameter values.
<p> This class uses a ConstVariableModelAnalysis to determine which
scheduling parameters are constants and which may change during
execution of the model. Rate parameters that can change are checked
to ensure that their change context is not strictly contained by the
model being scheduled. If this is the case, then the actor is not
locally synchronous, and cannot be statically scheduled. Dynamic
parameters with a valid changed context are treated symbolically when
computing the repetitions vector.
<p> After computing a schedule, this scheduler determines the external
rate of each of the model's external ports. Since the firing vector
is only computed symbolically, these rates can also only be computed
symbolically. The dependence of these external rates on the rates of
ports in the model is declared using a DependenceDeclaration. Higher
level directors may use this dependence information to determine the
change context of those rate variables and may refuse to schedule the
composite actor if those rates imply that this model is not locally
synchronous.
<p> This scheduler uses a version of the P-APGAN scheduling algorithm
described in [1].
<p> [1] B. Bhattacharya and S. S. Bhattacharyya. Quasi-static scheduling of
reconfigurable dataflow graphs for DSP systems. In <em> Proceedings of the
International Workshop on Rapid System Prototyping </em>,
pages 84-89, Paris, France, June 2000.
Author(s): Stephen Neuendorffer, Shuvra S. Bhattacharyya
Version:$Id: PSDFScheduler.doc.html,v 1.1 2006/02/22 18:41:22 mangal Exp $
Pt.Proposed Rating:Red (neuendor)
Pt.Accepted Rating:Red (neuendor)