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A PETRI NET MODEL OF A MODULAR, MICROPROGRAMMABLE COMPUTER (LM2)

IP.com Disclosure Number: IPCOM000128704D
Original Publication Date: 1975-Dec-31
Included in the Prior Art Database: 2005-Sep-16
Document File: 10 page(s) / 37K

Publishing Venue

Software Patent Institute

Related People

J. D. Noe: AUTHOR [+4]

Abstract

A Petri Net Model of a Modular, Microprogrammable Computer (IM4) J. D. Noe and T. H. Kehl Department of Computer Science University of Washington Seattle, Washington 98195 The recently developed Logic Machine Minicomputer utilizes a micro-programmable control processor interacting with specialized modules commun-icating over a shared bus, in order to implement a variable-structure architecture. The resulting cooperative processing can be difficult to describe with conventional methods. Modified Petri nets were investigated to examine their applicability to this level of modeling and were found to provide a means for characterizing the flow of control caused by macro-instructions establishing interactions among the hardware modules and micro-routines. The paper presents the resulting description of the minicomputer's internal operation with emphasis on the modeling method.

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THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

A PETRI NET MODEL OF A MODULAR, MICROPROGRAMMABLE COMPUTER (LM2)*

J. D. Noe and T. H. Kehl

.(Technical Report #75-09-01)

Department of Computer Science University of Washington Seattle, Washington 98195

N Supported by NSF (GJ28781 and GJ36273) and NIH DRR-BRB-RR 00374.

ABSTRACT

A Petri Net Model of a Modular, Microprogrammable Computer (IM4)

J. D. Noe and T. H. Kehl

Department of Computer Science University of Washington Seattle, Washington 98195

The recently developed Logic Machine Minicomputer utilizes a micro-programmable control processor interacting with specialized modules commun-icating over a shared bus, in order to implement a variable-structure architecture. The resulting cooperative processing can be difficult to describe with conventional methods. Modified Petri nets were investigated to examine their applicability to this level of modeling and were found to provide a means for characterizing the flow of control caused by macro-instructions establishing interactions among the hardware modules and micro-routines. The paper presents the resulting description of the minicomputer's internal operation with emphasis on the modeling method.

INTRODUCTION

A modified form of Petri Nets called Pro-Nets [11 (the name being derived from processes and processors) has been introduced for description and analysis of computer systems, particularly those embodying concurrent activities. Pro-Nets evolved from experience in applying E-Nets [2,31 to modeling a variety of systems. In this paper, Pro-Nets are used only for their descriptive capa-bility, for the purpose of explaining the operation of a distributed-control machine that is difficult to describe with more conventional means. This machine, the Logic Machine Mini- computer (LM 2 ) [4], employs a microprogrammable control processor and a number of specialized functional units communicating over a bi-directional bus. Most of the control is centralized, but some is delegated to local control in the functional units. This decreases the required communication band-width on the bus and provides other advantages: Local read only memory (ROM) control within the functional units allows a variety of responses to the same micro-program in the control processor, thus providing both economy and speed. Definition of new functional units is open-ended -- one is not constrained to a fixed set of modules -- so design of a whole family of machines can be accommodated by micro-programming to incorporate the features of new functional units (5].

University of Washington Page 1 Dec 31, 1975

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A PETRI NET MODEL OF A MODULAR, MICROPROGRAMMABLE COMPUTER (LM2)

One by-product of this flexibility is the difficulty of describing the operation of the machines. Control is distributed and related events are con-current, sometimes in a quasi-parallel sense and sometimes in actual simultaneous operation. In short, the architecture is inte...