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IP reuse requires a verification strategy

Posted: 16 Dec 2005 ?? ?Print Version ?Bookmark and Share

Keywords:sean smith? denali software? ip? intellectual property? verification?

IP reuse has long been touted as one of the keys to enabling today's massive SoC designs. The concept of reuse seems simple and easy in theory, but there are a number of obstacles that design and verification teams must address to be successful, especially in the case of complex commercial IP cores.

One of the first things a design team must address is evaluating if the design IP meets requirements as provided. In most cases, the IP will require some level of reconfiguration or redesign.

After conquering the most obvious obstacles, design teams may start to feel confident that the hard part is over. Unfortunately, there are several other large and complex tasks that must be addressed to ensure successful IP integration and reuse.

The most critical of these is the functional verification of the design IP, which is usually the most underestimated task. "Why do I need to test it?" and "The IP vendor already tested it, so I don't need to test it!" are phrases often heard when this subject is first broached. Unfortunately, for people striving to reuse design IP, it's not as simple as that. In reality, solid engineering work must be done to understand this aspect of IP reuse and to ensure success.

Choosing a strategy
The process of determining the verification strategy for a piece of design IP involves some important steps. One of the first is to understand the IP provider's verification process and review their verification plan and efforts to date. The particular verification methodology used by an IP vendor can greatly affect the quality and reusability of the IP.

To effectively evaluate the IP provider's verification strategy, the IP consumer must start by creating their own verification plan specific to the target application. Users need to sit down and come up with a list of important features and functions that are critical for their implementation.

In creating any verification plan, it's important to prioritize test-plan items. Once that effort has been initially completed, it becomes much more straightforward to review the provider's verification plan and see how well it is aligned with user goals for this IP usage.

It is equally important to ensure that the IP provider has a viable process and infrastructure for changing functional configurations of the IP and verifying those changes. Understanding the methodology used, how different configurations were tested and what types of coverage were measured will help the verification team understand what, and how much, they need to test.

VIP importance
Good-quality verification IP (VIP) can offer value to teams trying to integrate a commercial IP core into their device, regardless of whether teams are testing for compliance or just testing the integration of the core into the target system. In the recent past, commercial VIP often only consisted of a bus-functional model (BFM) and may have included a monitor to do some protocol checking. For VIP to be effective in enabling reuse of complex design IP, it needs to provide many more features and functions than just a BFM.

More modern commercial VIP offerings tend to be highly reconfigurable and offer more robust verification functionality, such as directed random stimulus generation, protocol and temporal checking, functional coverage metrics, and reusable stimulus libraries (scenarios). The concept of highly reconfigurable VIP stems from the nature of the highly configurable IP that people are trying to test. If the VIP cannot be reconfigured to match the ever-changing design IP, then it will not be of much value in verifying configurable IP.

Due to the complexity of today's protocols, directed stimulus is not an efficient way of verifying designs anymore. The time and effort required to generate stimulus by hand has become overwhelming. In its place, random constraint solvers that allow the user to generate interesting, complex and often unforeseen stimuluswith minimal effortare becoming widely accepted.

But having a constraint solver alone is not enough. For verification reuse to occur, VIP must provide easily or automatically configured stimulus libraries (scenarios) that are able to adapt to many different configurations and verification situations. These scenarios are more than simple test cases. They are reusable building blocks that enable teams to quickly and efficiently create the necessarily complex test cases.

In the case of interface IP blocks, the IP vendor can use VIP to encapsulate similar libraries of scenarios or streams of interface traffic for the customer to "replay" in the system environment. The end user can benefit from these scenarios in several ways. They will reduce the time it takes to get the first meaningful test running, but also allow you to complete tests with less effort and time.

Finally, functional coverage metrics give the VIP user an objective way to measure how much of the IP's functions and features have been exercised. In this case, functional coverage can be thought of as an electronic and executable version of a written test plan.

Functional coverage is an essential compliment to random stimulus generation. With directed random testing, users are not specifically targeting features, functions or even corner cases, but are using constrained randomness to exercise the design. Functional coverage determines if all interesting cases and features of the design have been hit. This is essential in answering the question, "Are we done testing yet?"

Despite all these challenges, there are clearly benefits to design IP reuse. Today's IP cores have the potential to not only address complex functionality, configurability and performance, but also provide a solution that allows for rapid and constant change of the design requirements.

Experts often cite functional verification effort at as much as 70 percent of the overall design effort. With such a large percentage of a project's resources devoted to verification, it only makes sense that verification reuse is as criticalif not more criticalthan design reuse.

One of the conclusions we can draw is that feasible reuse of IP cores requires vendors to invest in a solid methodology for dealing with the verification challenges associated with rapidly changing and widely varying IP configurations. VIP plays a key role in overcoming the verification and quality issues, which loom as one of the key barriers to IP reuse today.

Commercial IP vendors are increasingly leveraging configurable VIP solutions to increase the quality of IP-core verification. Likewise, designers are rapidly investing in reusable verification environments that leverage the same VIP for IP integration and local quality assurance, and to facilitate more efficient system-level verification.

Embracing verification reuse brings customers and vendors one step closer to realizing the benefits of IP reuse. If verification is up to 70 percent of the problem and users are primarily focusing on design IP, then they are only addressing 30 percent of the problem.

For real and substantial reuse benefits to be achieved, design teams must look at the problem of IP reuse as a whole and include all its aspects when looking for a solution. Design, verification, timing closure and test all play a part in the adoption and integration of a piece of IP. Don't make the mistake of focusing solely on the IP core when there are larger issues such as verification and system performance that must also be addressed to achieve the benefits of reuse.

- Sean Smith
Chief Verification Architect
Denali Software Inc.

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