3 research outputs found
Algorithm to layout (ATL) systems for VLSI design
PhD ThesisThe complexities involved in custom VLSI design together with the
failure of CAD techniques to keep pace with advances in the fabrication
technology have resulted in a design bottleneck. Powerful tools are
required to exploit the processing potential offered by the densities now
available. Describing a system in a high level algorithmic notation
makes writing, understanding, modification, and verification of a design
description easier. It also removes some of the emphasis on the physical
issues of VLSI design, and focus attention on formulating a correct and
well structured design. This thesis examines how current trends in CAD
techniques might influence the evolution of advanced Algorithm To Layout
(ATL) systems. The envisaged features of an example system are
specified. Particular attention is given to the implementation of one
its features COPTS (Compilation Of Occam Programs To Schematics).
COPTS is capable of generating schematic diagrams from which an
actual layout can be derived. It takes a description written in a subset
of Occam and generates a high level schematic diagram depicting its
realisation as a VLSI system. This diagram provides the designer with
feedback on the relative placement and interconnection of the operators
used in the source code. It also gives a visual representation of the
parallelism defined in the Occam description. Such diagrams are a
valuable aid in documenting the implementation of a design.
Occam has also been selected as the input to the design system that
COPTS is a feature of. The choice of Occam was made on the assumption
that the most appropriate algorithmic notation for such a design system
will be a suitable high level programming language. This is in contrast
to current automated VLSI design systems, which typically use a hardware
des~ription language for input. These special purpose languages
currently concentrate on handling structural/behavioural information and
have limited ability to express algorithms. Using a language such as
Occam allows a designer to write a behavioural description which can be
compiled and executed as a simulator, or prototype, of the system. The
programmability introduced into the design process enables designers to
concentrate on a design's underlying algorithm. The choice of this
algorithm is the most crucial decision since it determines the
performance and area of the silicon implementation.
The thesis is divided into four sections, each of several chapters.
The first section considers VLSI design complexity, compares the expert
systems and silicon compilation approaches to tackling it, and examines
its parallels with software complexity. The second section reviews the
advantages of using a conventional programming language for VLSI system
descriptions. A number of alternative high level programming languages
are considered for application in VLSI design. The third section defines
the overall ATL system COPTS is envisaged to be part of, and considers
the schematic representation of Occam programs. The final section
presents a summary of the overall project and suggestions for future work
on realising the full ATL system
Behavioural specification and simulation of minimum configuration computer systems.
The ultimate goal of Computer-Aided Design research in the area of digital circuits is the automatic synthesis of a complete solution from a behavioural specification. This thesis describes an attempt to attain this ideal in the more limited realm of designing single-board control systems, constructed from general-purpose microprocessor components. The difficulties currently encountered in designing and implementing microprocessor control systems are outlined, and the architecture of an integrated, knowledge-based design system is proposed as a method of overcoming these difficulties. The design system encompasses both behavioural and structural design functions. However, only the tools and techniques required to fulfil the behavioural design functions are considered in detail in this project.A review of previous work in the field of automated digital circuit design and software and hardware specification languages is presented. The major features of a novel language for specifying and simulating control system behaviour are then described, together with an intermediate design description notation, which facilitates the generation of microprocessor assembly language code directly from behavioural specifications. The design and implementation of a fast, generalised microprocessor simulation facility constructed from transputers is discussed, and its performance potential analysed. The simulation facility enables the complete design for a given application to be tested, before any actual hardware construction takes place. Finally, an evaluation of the behavioural specification, synthesis and simulation techniques developed in this project is presented, and the benefits perceived from adopting such techniques are summarised. Issues concerning the integration of these techniques with the knowledge-based structural design tools are also dealt with, and suggestions for further developments and enhancements are identified
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Transformational maintenance by reuse of design histories
This thesis provides theory and procedures for modifying software artifacts implemented by a formal transformation process. Installing modifications requires knowing not only what transformations were applied (a derivation history) to construct the artifact, but also why the application sequence ensures that the artifact meets its specification. The derivation history and the justification are collectively called a design history. A Design Maintenance System (DMS), when provided with a formal change called a maintenance delta, revises a design history to guide construction of a new artifact. A DMS can be used to integrate a stream of deltas into a history, providing implementations as a side effect, leading to an incremental-evolution model for software construction.We provide a broadly applicable formal model of transformation systems in which specifications are performance predicates, subsuming the functional specifications which are traditional for transformation systems. Such performance predicates provide vocabulary used in the design history to describe the effect of applying sets of transformations.A nonprocedural, performance-goal-oriented Transformation Control Language (TCL) is defined to control navigation of the design space for a transformation system. Recording the execution of a TCL metaprogram directly provides a design history.A complete classification of, and representation for, the set of possible maintenance deltas is given in terms of the inputs defined by the transformation system model. Such deltas include not only specification changes, but also changes to implementation support technologies. Delta integration procedures for revising derivation histories given functional or support technology deltas are provided, based on rearranging the order of transformations in the design space. Building on these operations, integration procedures that revise the design history for each type of delta are described. An agenda-oriented TCL execution process dovetails smoothly with the integration procedures.Our DMS is compared to a number of other maintenance systems. By using an explicit delta and verified commutativity, our DMS often reuses transformations correctly when others fail