Verification Vertigo

Perhaps the most common question at DAC is “What did you find that was new and interesting?” I often wonder if this is because they had not found anything themselves and need some ideas, or that there is so much information flying around, that they have problems sorting out the wheat from the chaff. Of course, there is a third possibility that there was nothing that was new and interesting within your field of interest. I have to admit that I have found myself in the same position some years, especially when the theme was in an area that was not central to my interests.

This year was easy for me. While DAC continues to short change verification, with almost all of the related sessions being pushed to Thursday afternoon, when most people are heading for home, the show floor was vibrant in the area of functional verification. The most notable for this year was the emergence of intelligent testbench tools. First I should define what I think they are before I talk about the options available.

An intelligent testbench can either replace or enhance existing simulation based or formal verification methodologies. Constrained random generation techniques manage to create huge quantities of stimulus, but at the end of the day they have difficulties both with closure (achieving the desired verification goals) and secondly with efficiency (huge server farms required). An intelligent testbench can help either by determining efficient stimulus sets or by finding ways to reach difficult to reach coverage points.

There were four tools on show at DAC this year, three of which are being shown for the first time. This number shows the need and the maturation of the technology necessary to implement them. Within those four entrants, they fell into two distinct classes, each of which had two examples. The first pair are those that work from a user created graph of the functionality. The two entrants in this field and inFact from Mentor Graphics and Trek from Breker Verification Systems, the only one that has appeared at DAC in the past. These tools derive the graph from the specification and thus have the ability to identify missing functionality in the design. On the downside, it requires the user to build the graph, which contrary to some peoples view does not imply graphics! The other two entrants create the graph from the design basically by performing simulation on the design and keeping track of the information required to create efficient paths through the design. While the way they do this is somewhat different, the end result is similar. The two entrants are from NuSym and from Avery. Both of these tools are in Beta testing at the moment. While they are based on the structure of the design, they require very small changes in the user environment, being able to make use of the existing testbenches.

I look forward to seeing all of these tools develop in the market, as the need for them is very real - especially as constrained random techniques begin to struggle with more complex designs.