Industry White Paper

Multi-Mode Clock Domain Crossing Verification Enables Analysis Efficiency and Accuracy

July 30, 2020 by Mentor, a Siemens Business


Today’s SoC designs employ advanced multi-clocking architectures to meet high-performance and low-power requirements. Since metastability from the intermixing of multiple clock signals is not modeled by digital simulation, we must perform exhaustive, automated Clock Domain Crossing (CDC) analyses to identify and correct problem areas to avoid unpredictable behavior when the chip samples come back from the fab. Given the breadth of end customers’ requirements, SoCs must support numerous configurations or “modes” for system start-up and configuration, BIST, end-customer use cases, and interface combinations. Being able to satisfy the need to perform extensive CDC analysis, and the high operational flexibility of the end product, poses a significant design and verification challenge.

In addition, while many SoC operational modes share a baseline clock and data path configuration, commonly there are a significant number of modes with different clock and data path configurations from the baseline and/or from each other. This means register paths that are “CDC safe” in a given mode can be a violation when the SoC is running in other legal modes. From an EDA methodology perspective, there is another layer of complexity to address: since the SoCs are so large (nearly 1 billion gates), we must perform the CDC analysis and aggregate the results in a hierarchical manner.

In this white paper by Mentor, a Siemens Business, explore how an automated modal CDC analysis can be used to exhaustively verify CDC issues in all test and operational modes of a large SoC with multiple IPs. Modal CDC analysis configures the design as a set of operational modes and runs CDC analysis on each modal version of the design. Before the modal analysis flow was adopted, users would have to manually set up CDC analysis runs for each of the parameter sets corresponding to each DUT mode. The main benefit of this new approach has come from the automatic consolidation of all the results from each mode, making issues very easy to interpret and debug. Now it only takes a few hours to review results and begin to take corrective action, vs. days and weeks with the prior, manual approach.

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