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Formally Verifying Data and Control with Weak Reachability Invariants

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Formal Methods in Computer-Aided Design (FMCAD 1998)

Part of the book series: Lecture Notes in Computer Science ((LNCS,volume 1522))

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Abstract

Existing formal verification methods do not handle systems that combine state machines and data paths very well. Model checking deals with finite-state machines efficiently, but model checking full designs is infeasible because the large amount of state in the data path. Theorem-proving methods may effective for verifying data path operations, but verifying the control requires finding and proving inductive invariants that characterize the reachable states of the system.

We present a new approach to verification of systems that combine control FSMs and data path operations. Invariants are specified only for a small set of control states, called clean states, where the invariants are especially simple.We avoid the need to specify the invariants for the unclean states by symbolically simulating over all paths to find the possible next clean states.

The set of all paths from one clean state to the next is represented by a regular expression, which is extracted from the control FSMs. The number of paths is infinite only if the regular expression contains stars. The method uses a heuristic to, generalize the symbolic state to cover all of the paths of the starred expression. We have implemented a prototype tool for guiding an existing symbolic simulator and verification tool and used it successfully to prove properties of the Instruction Fetch Unit of TORCH, a superscalar microprocessor designed at Stanford. With much less effort, we were able to find all the bugs in the unit that were found earlier by manually strengthening the invariants.

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Author information

Authors and Affiliations

  1. Computer Systems Laboratory, Stanford University, Stanford, CA, 94305, USA

    Jeffrey Su, David L. Dill & Jens U. SkakkebÆk

Authors
  1. Jeffrey Su
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  2. David L. Dill
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  3. Jens U. SkakkebÆk
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Editor information

Editors and Affiliations

  1. Department of Computer Science, University of Utah, 50 S Central Campus, Salt Lake City, UT, 841112-9205, USA

    Ganesh Gopalakrishnan

  2. Department of Computer Science, Brigham Young University, 3361 TMCB, Provo, UT, 84602-6576, USA

    Phillip Windley

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© 1998 Springer-Verlag Berlin Heidelberg

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Su, J., Dill, D.L., SkakkebÆk, J.U. (1998). Formally Verifying Data and Control with Weak Reachability Invariants. In: Gopalakrishnan, G., Windley, P. (eds) Formal Methods in Computer-Aided Design. FMCAD 1998. Lecture Notes in Computer Science, vol 1522. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-49519-3_25

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  • DOI: https://doi.org/10.1007/3-540-49519-3_25

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  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-540-65191-8

  • Online ISBN: 978-3-540-49519-2

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