Learning not to fear PCI Express compliance

By Mike Bartley and Jim Hutchinson, ClearSpeed Technology Plc
edadesignline.com (August 12, 2008)

Introduction

On the way to taping out its first PCI Express based SOC, ClearSpeed came face-to-face with the many difficulties of ensuring PCI Express protocol compliance within time and budget constraints. PCI Express is a complex protocol with an extremely large coverage space. From a management perspective, there is simply not an alternative but to apply a metrics-driven verification process to ensure protocol compliance. Unfortunately, even with thousands of tests covering the relevant scenarios, significant coverage holes remain, making this approach unpredictable and costly. The alternative, a general random test approach, isn't sufficiently predictable.

ClearSpeed has come to realize that the ideal approach yields significant benefits: it minimizes engineering effort while maximizing test deployment control. ClearSpeed got a head-start by using commercial PCIe Verification IP supplied by Cadence. The VIP, called a UVC, includes the Compliance Management System (CMS) which partitions and maps the coverage space to the PCIe specification. CMS also provides a compliance test suite in the form of constrained-random tests (called sequences) to automatically achieve high functional coverage for each PCIe specification section. ClearSpeed then built its own constrained random test suite on top of the UVC's. Associated coverage is analyzed after each test group run, resulting in clear understanding of where coverage holes lie and guiding where new tests must be directed to reach uncovered scenarios. This approach also has provided ClearSpeed with an invaluable project management tool since it helps them to understand and report on verification status. ClearSpeed now regularly tracks coverage, bug statistics, and test failures in each of the main specification areas.

The methodology, tools used, and implementation guidelines employed will be described including the best practices learned along the way. The paper will also describe the technical and business benefits that have accrued using this approach and how they will be deployed throughout our company going forward.

Background The ClearSpeed product range includes chips, accelerator cards, rack modules, software and support. ClearSpeed's chips, accelerator cards and rack modules are all designed to work with industry-standard x86-based systems. ClearSpeed chips are programmed in C and ClearSpeed offers the customer a complete IDE that works together with all the standard software development tools. This is diagrammed in Figure 1.

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