Cross-Level Processor Verification via Endless Randomized Instruction Stream Generation with Coverage-guided Aging

We propose a novel cross-level verification approach for processor verification at the Register-Transfer Level (RTL). The foundation is a randomized coverage-guided instruction stream generator that produces one endless and unrestricted instruction stream that evolves dynamically at runtime. We lever-age an Instruction Set Simulator (ISS) as a reference model in a tight co-simulation setting. Coverage information is continuously updated based on the execution state of the ISS and we employ Coverage-guided Aging to smooth out the coverage distribution of the randomized instruction stream over the time. In combination, this enables a broad and deep coverage to find intricate corner-case bugs in the RTL processor. Our case study with an industrial pipelined 32 bit RISC- V processor demonstrate the effectiveness of our approach.