Applying Constrained-Random Verification to Microprocessors

Constrained-random verification (CRV) offers a highly effective way to deal with the challenges of microprocessor verification. These verification challenges are overwhelming for many reasons: complex instruction sets, multiple pipeline stages, in-order or out-of-order execution strategies, instruction parallelism, fixed- and floating-point scalar/vector operations, and other features that create a seemly never-ending list of corner cases to exercise. The time required to create traditional directed tests has become unreasonable.

Language features such as the SystemVerilog random sequence generator allow you to create instruction sequences randomly to improve stimulus quality based on a structured set of rules and scenarios. Such random-sequence generation schemes are procedural, however, and do not take full advantage of object-based randomization using constraints.

This article proposes an object-oriented solution for processor verification challenges. The solution covers both a top-down stimulus planning process and a bottom-up implementation solution using SystemVerilog and commercially available base classes (such as those in Synopsys's Verification Methodology Manual, VMM). The description that follows covers the most important parts of this solution and uses a processor supporting the MIPS-I instruction set as an example design under test (DUT).

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