Multi-level synthesis for safe replaceability

We describe the condition that a sequential digital design is a safe replacement for an existing design without making any assumptions about a known initial state of the design or about its environment. We formulate a safe replacement condition which guarantees that if an original design is replaced by a new design, the interacting environment cannot detect the change by observing the input-output behavior of the new design; conversely, if a replacement design does not satisfy our condition an environment can potentially detect the replacement (in this sense the replacement is potentially unsafe). Our condition allows simplification of the state transition diagram of an original design. We use the safe replacement condition to derive a sequential resynthesis method for area reduction of gate-level designs. We have implemented our resynthesis algorithm and we report experimental results.

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