In this work we investigate the integration of SAT methods into a simulation-based sequential ATPG tool, STRATEGATE [11], with the aim of improving the state-of-the-art in sequential ATPG. We offer a detailed analysis of possible scenarios and algorithms for performing such an integration. Our preliminary investigations show that such hybrid approaches can be very promising.
½ ÁÒØÖÓ Ù Ø ÓÒThe sequential ATPG problem has been widely investigated for over three decades. However, despite several advancements in this area, it remains an intractable problem of significant practical importance for the core task of manufacture testing [8,11,21] as well as for design verification [2,5,26,28]. In recent years CNFbased SAT solvers [7,18,19,33] have emerged as a powerful technology for Boolean reasoning in EDA applications [4,15,31]. In this work we discuss how SAT methods may be applied to the sequential ATPG problem. This research is motivated by the industrial success of multiengine or hybrid methods in areas such as combinational equivalence checking [14,20] and property checking [9]. The key idea here is to use a carefully orchestrated combination of orthogonal core engines such as BDDs, SAT, simulation, circuit-based ATPG etc. to efficiently solve the overall problem, by using each engine to solve a portion of the problem that it is best suited to. This work aims to apply this philosoply to sequential ATPG. Specifically, our final objective is a fine-grained integration of a powerful SAT solver such as Chaff [19] with a state-of-the-art simulationbased sequential ATPG tool such as STRATEGATE [11].STRATEGATE is based on smart simulation-oriented methods, which are incomplete, while modern SAT solvers implement complete algorithms based on branch-and-bound search, enhanced with learning techniques [18]. These algorithmic features are naturally complementary and hence well-suited for being combined into a more powerful reasoning engine. Moreover, SAT methods have been able to make an impact in areas such as combinational ATPG [15,31] and combinational equivalence checking [20,23], which were thought to be the forte of more traditional technologies such as BDDs or network and rule-based branch-and-bound engines. Therefore, we strongly believe that SAT solvers can significantly improve the state-of-the-art in sequential ATPG.The main contribution of this work is the development of methods for combining state-of-the-art simulation-based sequential ATPG algorithms with efficient (deterministic) SAT techniques. Specifically, we identify places in the sequential ATPG flow of STRATEGATE where SAT methods could symbiotically work with and enhance the existing algorithms, formulate appropriate problems in this flow as SAT problems, and experimentally analyse the comparitive performance of the SAT-based formulation and the STRATEGATE algorithms on these problems. However, the proposed ideas can be used to enhance any simulation-based sequential ATPG framework. We would like to emphasize that this work is meant to be a proof of con...