True story: this series of blog posts is inspired by a dream. I recently gave a presentation on the Cadence verification business to our CEO and several members of the Executive Management Team. Naturally, I took this presentation seriously and spent a lot of time preparing the material and thinking through the key points to cover in the limited time I would have with this high-powered audience. The prep work must have occupied my subconscious as well since the night before the actual event I dreamt that I was giving the presentation.
In my dream, I initially droned on through a bunch of PowerPoint slides but then enlivened the meeting by moving through a series of sets ranged around the conference room. Each set was based upon a famous movie, and a group of actors joined me in each set as we staged a scene from the movie to illustrate some sort of point about verification. That would have been great fun in real life, but of course I had neither the time nor the budget for such an extravaganza. Instead, I offer this offbeat take on metric-driven verification (MDV) using movie quotes.
When we talk about MDV, we start by noting that all verification engineers go through a similar four-phase cyclic process:
• They develop some sort of a plan for what they intend to verify
• They construct a testbench or verification environment
• They run tests using this environment
• They measure and analyze the results and either repeat the cycle or decide that they’re done
The traditional verification approach follows this process, but in a very simple way. The plan is typically nothing more than a list of tests that the verification team intends to write. They construct a very simple testbench and write a directed test by hand to exercise a specific part of the design. This test is run on a simulator, and the results are analyzed. Sometimes the test is self-checking, but in other cases the engineers may manually examine waveforms to determine if the test passed. They declare verification done when all planned tests are written and passing.
Such a simple approach does not suffice for verifying large or complex designs. That’s when MDV comes in to play by automating this process, speeding up each cycle, reducing the number of cycles, and providing the best possible metrics to determine when to stop. The following diagram shows the end result of applying the Cadence MDV flow to the standard cyclic verification process:
Good verification planning is all about communication and goes beyond just documenting intended tests. For a start, the automated MDV flow relies primarily on constrained-random stimulus rather than hand-written tests. A constrained-random testbench may exercise many parts of the design at once, so high-quality coverage metrics are needed. These metrics identify key parts of the design that must be exercised, communicating critical knowledge from both the design and verification engineers.
MDV supplements coverage with other types of metrics, such as correctness checks, that communicate critical information on the proper operation of the design. All these metrics are captured in the vPlan, an online, executable verification plan. Metrics results are gathered during the run phase and automatically reported back against the online plan. This is far safer and far more comprehensive than the traditional manual verification process. Verification is deemed complete only when all coverage metrics have been exercised and all checks are passing.
The Cadence MDV flow adds an additional, unique form of communication: between the design’s functional specification and the vPlan. As architects or marketing staff develop the specification, they can annotate it with links between specific features and specific metrics in the vPlan. Cadence Enterprise Planner can then correlate the two representations. If the specification is modified to add or delete a feature, Enterprise Planner will report that the vPlan is now out of date. This is an invaluable link, especially late in a project when such changes are often missed.
So the MDV flow ensures that there is no “failure to communicate” among marketing, architects, designers, and verification engineers during the planning phase. Of course, MDV aids the other three phases as well. These will be discussed in subsequent blogs posts, along with appropriate quotes from Hollywood movies. If you have other favorite quotes that you’d like to suggest, please post a comment!
The truth is out there...sometimes it's in a blog.