Clairvoyant: A Synthesis System for Production-Based Specification

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Clairvoyant A Synthesis System for
Production-Based Specification

• IEEE Transactions on VLSI Systems (June 1994)
• A. Seawright, F. Brewer
• Presented by Jun Zhu

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Outline

• Background
• Production-Based-Specification
• Clairvoyant Implementation
• Discussion

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Background

• Specification level - To address complex, the
  non-determinism production-base-specification is
  introduced.
• Sequential synthesis level - Use symbolic Boolean
  Decision Diagrams to derivate a deterministic
  machine.

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Production-based-specification

• PBS is a hierarchical set of productions,
  including
• Symbols
• Operators
• action clauses
• Two composition symbols of productions
• Sequential production
• Boolean productions
• Extended Composition Operators
• Concatenation ( , )
• Closure ( )
• Or ( , )
• And ( , )
• Not ( ! , )
• Recursion of production is not allowed.

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Action is executed when its antecedent production
is recognized.

( 1 ) Regular expression
( 2 ) Production representation
P1
P1
P3
P3
P2
P2
P4
P4
P5
( 3 ) Production DAG (Directed Acyclic Graph)
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• Execution model
• The behavior of the PBS is determined by the
  execution of the control flow.
• Several actions may be triggered simultaneously.
• Data dependencies between actions are important.
• e.g Two actions action1x0, action2xx1
• Order1 ? x 0
• Order2 ? x 1.

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• B) Operators
• Sequential operators are a superset of the
  classical expression operators
• Exception operators are designed for exception
  handling, re-synchronizations and recovery
  mechanisms.
• e.g Exception operators - Considering the
  following nest productions
• a -gt b !! c
• b -gt d !! e
• d -gt

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Clairvoyant Implementation

• Intermediate Machine Representation
• State transition function Bn Bk ?Bn
• Output function Bn ?Bm
• ?(x1, x2,, xn) (z1, z2,, zk) ? (y1,
  y2,, yn)
• Represents a deterministic state transition
  function.
• ?(x1, x2,, xn) ? (U1, U2,, Ul)
• Moore form output function
• ?(x1, x2,, xn) ? (a1, a2,, am)
• Mealy form output function

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• Construction of the Intermediate Machine
• Input of the Build procedure
• A pointer of a node of the production DAG
• An excitation function
• Output of the Build procedure
• A boolean function on the recognition of the
  current sub-DAG
• Initiation
• A pointer of the top-level node of the production
  DAG
• An excitation function of the initial control
  point
• Work in a recursive bottom-up fashion
• Each time a leaf of the production DAG is
  reached, a new control point is added to the
  state vector.
• At intermediate nodes, left and right submachines
  are composed.

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• Action condition

(x3 x2) t2 x4
3
Action2
2
Action1
1
(x5 x1) t2 x6
t3 x1 x7
a cycle earlier
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Binary decision tree True table
variable ordering x1ltx2ltx3
Binary Decision Diagram (BDD)
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Variable Ordering in BDD
Boolean function
Order1
Order2
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• BDD in Clarivoyant
• a reasonable heuristic variable ordering based on
  circuit topology arguments and the precedence
  relations
• reachable state analysis on the constructed
  intermediate machine

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• Discussion
• Binary Decision Diagram is a bridge between
  production-based-specification and circuit
  synthesis?