Smart Simulation Using Collaborative Formal and Simulation Engines

Pei-Hsin Ho

Abstract

We present Ketchum, a tool that was developed to improve the productivity of simulation-based functional verification by providing two capabilities: (1) automatic test generation and (2) unreachability analysis. Given a set of "interesting" signals in the design under test (DUT), automatic test generation creates input stimuli that drive the DUT through as many different combinations (called coverage states) of these signals as possible to thoroughly exercise the DUT. Unreachability analysis identifies as many unreachable coverage states as possible.

Ketchum differs from the previous published results for several reasons. First, Ketchum provides 10x higher capacity than previous published results. The higher capacity is achieved by carefully orchestrating simulation and multiple formal methods including symbolic simulation, SAT-based BMC, symbolic fixpoint computation and automatic abstraction. Second, Ketchum performs not only automatic test generation but also unreachability analysis, which enables the test generation effort to be focused on coverage states that are not unreachable. Third, the backbone of Ketchum is an off-the-shelf commercial simulator. It enables Ketchum to reach deep states of the design quickly and supports simulation monitors through the standard API of the simulator during test generation.

We applied Ketchum to several industrial designs, including the picoJava microprocessor from SUN and the DW8051 microcontroller from Synopsys and obtained very promising results. The experiments show that Ketchum can (1) handle design blocks containing more than 4500 latches and 170K gates, (2) reach up to 6x more coverage states than random simulation and (3) identify a majority of the unreachable coverage states.

This is joint work with Thomas Shiple, Kevin Harer, James Kukula, Robert Damiano, Valeria Bertacco, Jerry Taylor and Jiang Long. The same work will also be presented at ICCAD2000 in November.


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