Clock domain crossings (CDC) continue to be a trouble spot for functional verification. With the number of clock domains increasing in today's complex system designs, the ability to thoroughly verify CDC has become even more important. Traditional methods have come up short in fully verifying and controlling metastability, the primary manifestation of CDC errors. Fortunately, new tools and methodologies are available to address these shortcomings.

In order to get a handle on this complex problem, this paper gives an overview of the causes and effects of metastability along with a review of the traditional strategies that have generally failed to fully address CDC problems. With this background in place, the paper progresses to a discussion of the techniques and methodologies required to successfully identify all CDC errors.

Finally, a practical solution is presented that has already been proven on real-world designs. The Mentor Graphics Questa CDC solution integrates advanced verification engines with engineered methodologies. It provides a systematic and comprehensive way to ensure that

CDC is handled reliably at the design stage, thus avoiding costly redesign of fielded products.