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Abstract. This paper presents an innovative tool used during the verification of the UltraSPARC #IIIi (TM) processor. UltraSparc #IIIi operates in a multi-processor environment. Verifying the robustness of the cache coherency maintaining parts of the design was one of the main challenges facing the functional verification team. The team adopted a combination of standard, "classic" techniques and methodologies, as well as some new innovative approaches. This mixture of old and new led to a well-balanced, robust verification flow which enabled finding the majority of the design problems (bugs) early in the pre-silicon stage of the project. This paper discusses an internal tool (Sniper) (patent pending) which increases the processor bus activity in a way which would uncover subtle coherency problems. Architecture OverviewThe UltraSPARC #IIIi processor is a third generation 64b 4-instruction issue SPARC(TM) RISC processor which supports high-end desktop workstations and workgroup servers with focus on higher system integration and cost reduction. The chip operates at 1.1GHz to 1.4GHz. The processor core uses a 14-stage pipeline described in [1,2,3] that supports the concurrent launch of up to six instructions which can consist of 2 integer operations, 2 floating point operations, 1 memory operation and 1 control transfer instruction.[5] On-chip, level 1 caches include 64KB 4-way data cache, a 32KB 4-way instruction cache, a 2KB 4-way data prefetch cache, and a 2KB 4-way write cache. The instruction and data caches have data parity protection. The design includes a 1MB on-chip, (64B line size) level 2 cache that is used for both instruction and data caching. It implements a pseudo-random cache line replacement algorithm. The level 2 cache is a writeback, write-allocate cache, supporting the MOESI coherency protocol.[5] The proprietary 200MHz, 128 bit system interface (JBUS) enables processors and other bus agents to communicate via the shared address and data bus with 3.2GB/s maximum bandwidth.[5] The on-chip memory controller