Computer Laboratory

Technical reports

Executing behavioural definitions in higher-order logic

Albert John Camilleri

July 1988, 183 pages

This technical report is based on a dissertation submitted February 1988 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Darwin College.

Abstract

Over the past few years, computer scientists have been using formal verification techniques to show the correctness of digital systems. The verification process, however, is complicated and expensive. Even proofs of simple circuits can involve thousands of logical steps. Often it can be extremely difficult to find correct device specifications and it is desirable that one sets off to prove a correct specification from the start, rather than repeatedly backtrack from the verification process to modify the original definitions after discovering they were incorrect or inadequate.

The main idea presented in the thesis is to amalgamate the techniques of simulation and verification, rather than have the latter replace the former. The result is that behavioural definitions can be simulated until one is reasonably sure that the specification is correct. Furthermore, proving the correctness with respect to these simulated specifications avoids the inadequacies of simulation where it may not be computationally feasible to demonstrate correctness by exhaustive testing. Simulation here has a different purpose: to get specifications correct as early as possible in the verification process. Its purpose is not to demonstrate the correctness of the implementation – this is done in the verification stage when the very same specifications that were simulated are proved correct.

The thesis discusses the implementation of an executable subset of the HOL logic, the version of Higher Order Logic embedded in the HOL theorem prover. It is shown that hardware can be effectively described using both relations and functions; relations being suitable for abstract specification and functions being suitable for execution. The difference between relational and functional specifications are discussed and illustrated by the verification of an n-bit adder. Techniques for executing functional specifications are presented and various optimisation strategies are shown which make the execution of the logic efficient. It is further shown that the process of generating optimised functional definitions from relational definitions can be automated. Example simulations of three hardware devices (a factorial machine, a small computer and a communications chip) are presented.

Full text

PDF (8.1 MB)

BibTeX record

@TechReport{UCAM-CL-TR-140,
  author =	 {Camilleri, Albert John},
  title = 	 {{Executing behavioural definitions in higher-order logic}},
  year = 	 1988,
  month = 	 jul,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-140.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-140}
}