Showing papers on "Petri net published in 1974"

Analysis of asynchronous concurrent systems by timed petri nets

Abstract: This thesis is concerned with the modeling and performance analysis of systems which consist of concurrently acting components, an example of which is an asynchronous pipelined processor. The work is divided into two parts. In the first part, a suitable model is developed for describing the structure of asynchronous concurrent systems. In conventional automata theory, the finite-state machine model is used to describe the behavior of systems; the problem with this is that a large number of states results when practical systems are modeled. In this thesis, each system component is modeled as a finite-state machine, and a system is viewed as an ensemble of interconnected finite-state machines. This has the advantage that the size of a system model grows linearly rather than exponentially with the number of system components. A subclass of Petri nets known as SMD (State Machine Decomposable) Petri nets is identified in order to formalize the notions of finite-state machines and their inter-connection. For convenience, systems of interest are divided into two broad categories: (a) deterministic, or decision free, (b) non-deterministic, or systems with decisions. SMD Petri nets are used to model both classes of systems; in addition, a subclass of Petri nets known as LSP Petri nets is used to model those deterministic systems that cannot be modeled by SMD Petri nets. The second part of the thesis is concerned with finding the computation rate of activities in real-world asynchronous concurrent systems. Practical systems are constructed from devices which have a finite speed of operation. Since Petri nets do not have time parameters as part of their definition, they can model the structure of systems but cannot be used to study their computation rate. The definition of Petri nets is augmented to model the speed of operation of a device in a system by assuming that the corresponding activity in the Petri net has a finite, non-zero time duration. The resulting nets are termed timed Petri nets, and methods are given for finding the computation rate of activities in times SMD and LSP Petri nets. The results are applied to the analysis of several asynchronous systems drawn from areas within and outside the domain of computer systems.

Cellular arrays for asynchronous control

Abstract: The microprogrammed controls which have evolved following Wilkes' suggestion are for synchronous control structures. This paper presents a micro-programmable array for realizing an asynchronous control structure. The work presented here extends Jump's asynchronous control arrays to include many essential control capabilities which were lacking. The arrays realize structures which allow sequencing of operations, conditional branch, subroutine call, fork operation to create parallel processes, join of parallel processes, merging of control, and arbitration with semaphore primitives to achieve controlled access to limited resources. The control to be realized is specified as a Simple Petri net which is then translated into an array representation which represents the microprogram. The cellular array is then obtained by selecting cell configurations in accordance with the node of the array representation of the control. The circuits obtained are asynchronous and speed independent. The microprogrammed array is a cellular form of C, S, NOR, XOR synthesis of Petri Nets.

Petri-Netze und asynchrone Schaltwerke / Petri-nets and asynchronous sequential circuits

Abstract: Es werden die Möglichkeiten aufgezeigt, welche Petri-Netze als Darstellungsmittel bei der Analyse und Synthese von Schaltwerken bieten. Die Netze werden als konsequente Weiterentwicklung von Zustandsgraphen dargestellt. Als Sonderfall wird das Aktionennetz betrachtet, welches zur Beschreibung und Realisierung von Steuerflüssen für Parallelprozeßsysteme dient. Dabei wird ein einfaches Aktionenschaltwerk eingeführt. Am Beispiel einer Standardschnittstelle wird demonstriert, wie man durch einfache Zuordnung von Signalflanken zu Netzereignissen zu einem Petri-Netz gelangt, welches die Funktion eines gegebenen Systems verkoppelter asynchroner Schaltwerke geschlossen und übersichtlich beschreibt.

Performance Evaluation of a Process Control System by Simulation Model

Abstract: In this paper the problems met with in the performance evaluation of a process computer system are faced. After pointing out the meaning of performance evaluation for such an application and identifying the set of measurements characterising the behaviour of the controlled physical process and the computer system, the evaluation method employed is described; this consists of a set of direct software measurements and a simulation model fed by event trace. The simulation model structure is analysed and some problems relating to its feeding are illustrated. To facilitate choice of the set of measurements to be carried out and their interpretation, the system behaviour is described through a model derived from the Petri net. Finally, the results relative to the behaviour of a computer system dedicated to the control of a gaschromatographic laboratory is reported.