High level static analysis of system descriptions for taming verification complexity

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Vasudevan, Shobha

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The growing complexity of VLSI and System-on-a-chip(SoC) designs has made their verification extremely expensive, time-consuming and resource intensive. Formal verification of system behavior is critical to the design cycle due to its ability to isolate subtle flaws and provide high quality assurance. However, its computational intractability limits applicability in practice, rendering the state-of-the-art insufficient to meet the needs of the industry. In this dissertation, a suite of techniques that are a significant departure from traditional Boolean level approaches to formal verification are presented. The algorithms are based on a top-down, domain-aware perspective of the system by reasoning at the system level and register transfer level (RTL) descriptions. Static analysis of these high level system descriptions using structural information and symbolic reasoning leads to effective decomposition strategies that create tractable portions of the system. These manageable system components can then be verified by deploying efficient Boolean level algorithms. The techniques presented here apply to the actual RTL source code, and are intended to blend seamlessly into the system design cycle. All approaches using high level static analyis follow a three pronged solution- domain aware analysis, high level symbolic simulation and a decision procedure for the verification task. This work advocates a marked difference in the perspective to formal hardware verification as compared to popular paradigms. The techniques shown here are illustrative of a hardware-aware viewpoint to verification, and argue this case for contemporary verification tasks. Antecedent conditioned slicing, an abstraction technique for reducing RTL design space is introduced. The reduced RTL can then be model checked. An open source RTL implementation of the USB 2.0 protocol is verified using this technique. A technique for pipelined processor verification using antecedent conditioned slicing is introduced. An open source Verilog RTL of OR1200, an embedded processor is explained in a detailed case study for verification using this technique. A static analysis technique is proposed to alleviate the complexity of the sequential equivalence checking problem between system level and RTL descriptions, by efficiently decomposing designs using sequential compare points. A satisfiability (SAT) solver is used as the lower level verification engine. In a case study, sequential equivalence checking between a system level description of a Viterbi decoder and two different RTL implementations are detailed.