I want to use jaspergold to formally verify functionality of my custom multiplier. I am computing the expected result using A*B to check against output of my multiplier. Here, A and B are two logic signed operands. However, jaspergold is performing the operation A*B incorrectly.

I have reproduced this issue using the attached example. JasperGold compiles and elaborates the module and subsequently runs a formal proof. The tool raises a counterexample to assertion whose screenshot is attached below:

I simulated the same example using xrun and it was giving the correct product output in simvision waveform. Please help me resolve this issue. I am using 2023.03 version of Jasper Apps.

Thanks and regards

Anubhav Agarwal

Formal verification is a complex technology that has traditionally required experts or specialized teams who stood apart from the IC design and verification flow. Taking a different approach, a new release of the Cadence JasperGold formal verification platform (June 8, 2015) provides formal techniques that complement simulation, emulation, and debugging in the form of “Apps” or under-the-hood solutions that any design or verification engineer can use.

JasperGold was the initial (in fact only) product of Jasper Design Automation, acquired by Cadence in 2014. Jasper pioneered the formal Apps concept several years ago. While the company had previously sold JasperGold as a one-size-fits-all solution, Jasper began selling semi-automated JasperGold Apps that solved specific problems using formal analysis technology.

The new release is the next generation of JasperGold and will be available later this month. It includes three major improvements over previous Cadence and Jasper formal analysis offerings:

• A unified Cadence Incisive and JasperGold formal verification platform delivers up to 15X performance gain over previous solutions.
• JasperGold is integrated into the Cadence System Development Suite, where it provides formal-assisted simulation, emulation, and coverage. As a result, System Development Suite users can find bugs three months earlier than existing verification methods.
• JasperGold’s formal analysis engines are integrated with the recently announced Indago debug platform, automating root cause analysis and on-the-fly, what-if exploration.

Best of Both Formal Verification Worlds

Taking advantage of technologies from both Cadence and Jasper, the new JasperGold represents a “best of both worlds” solution, according to Pete Hardee, product management director at Cadence. This solution combines technologies from the Cadence Incisive Enterprise Verifier and Incisive Formal Verifier with JasperGold formal analysis engines.

For example, to ease migration from Incisive formal tools, Cadence has integrated an Incisive common front end into the JasperGold apps platform. Jasper formal engines can run within the Incisive run-time environment. Cadence has also brought some selected Incisive formal engines into JasperGold.

As shown to the right, the JasperGold platform supports both the existing JasperGold front-end parser and the Incisive front-end parser. Hardee observed that this dual parser arrangement simplifies migration from Incisive formal tools to JasperGold, and provides a common compilation environment for people who want to use JasperGold with Incisive simulation. Further, the common run-time environment enables formal-assisted simulation.

The combination of JasperGold engines and Incisive engines supports two use models for formal analysis: formal proofs and bug hunting. In the first case, formal engines try all combinations of inputs without a testbench. The test is driven by formal properties written in languages such as SVA (SystemVerilog assertions) or PSL (Property Specification Language). Completion of a property is exhaustive proof that something can or cannot happen. This provides a “much stronger result” than simulation, Hardee said.

He also noted that formal analysis doesn’t necessarily require that all properties are completed. “You can get a lot of value even if proofs don’t complete,” he said. “Proofs that run deep enough to find bugs are just fine.”

Bug hunting involves random searches, and JasperGold bug hunting engines are very fast. However, these engines don’t necessarily use the most optimal path to get to a bug. So, Cadence engineers brought a constraint solver from Incisive and integrated it into JasperGold. “It looks at the constraints in the environment and gives you a better starting point,” Hardee said. “It takes more up-front time, but once you’ve done that the bug hunting engines can actually take a shorter path and find a bug a lot quicker.”

Another new JasperGold capability from the Incisive Formal Verifier is called “search pointing.” This uses simulation to penetrate deeply into the state space, and then kicks off a random formal search from a given point that you’ve reached in simulation. This technique makes it possible to find bugs that are very deep in the design.

It is probably clear by now that a number of different formal “engines” may be required to solve a given verification problem. Traditionally, a formal tool (or user) will farm a problem out to many engines and see which one works best. To put more intelligence into that process, Cadence launched the Trident “multi-cooperating engine” a couple of years ago. That has now been brought into JasperGold, where it helps “orchestrate” the engines according to what will work best for the design. This is a big part of the reason for the 15X speedup noted earlier in this post.

Integration with System Development Suite

The Cadence System Development Suite is an integrated set of hardware/software development and verification engines, including virtual prototyping, Incisive simulation, emulation, and FPGA-based prototyping. As shown below, JasperGold technology is integrated into the System Development Suite in several places, including formal-assisted debug, formal-assisted verification closure, formal-assisted simulation, formal-assisted emulation, and the Incisive vManager verification planning tool.

Formal-assisted emulation sounds like it should be easy, especially since Cadence has both accelerated verification IP (VIP) and assertion-based VIP. However, there’s a complication. Accelerated VIP represents less verification content than simulation VIP, because you have to remove many checkers to get VIP to compile on a Palladium emulator. That’s because the Palladium requires synthesizable code.

What you can do, however, is use assertion-based VIP in “snoop mode” as shown below. Assertion-based VIP coded in synthesizable SystemVerilog can replace the missing checkers in accelerated VIP. In this diagram, everything in the green box is running in the emulator and is thus completely accelerated.

 

Another example of formal-assisted emulation has to do with deep traces. As Hardee noted, emulation will produce very long traces, and it can be very difficult to find a point of interest in the trace and determine what caused an error. With formal-assisted emulation, users can find interesting events within the traces and create properties that mark them, so a debugger can find these events and trace back to the root cause.

Formal-assisted verification closure is available with the new JasperGold release. This is possible because you can use the vManager product to determine which tasks were completed by formal engines. It’s important information for verification managers who are not used to formal tools, Hardee noted.

Another aspect of formal-assisted verification closure is the JasperGold Unreachability Analysis (UNR) App, which can save simulation users weeks of time and effort. This App takes in the simulation coverage database and RTL, and automatically generates properties to explore coverage holes and determine if holes are reachable or unreachable. The App then generates an unreachable coverage point database. If the unreachable code does something useful, there’s a bug in the design or the testbench; if not, you don’t have to worry about it. The diagram below shows how it works.

Formal-Assisted Debugging

The third major component of the JasperGold announcement is the integration of formal analysis into the Indago debugging platform. As shown below, this platform has several apps, including the Indago Debug Analyzer. Two formal debug capabilities from the Jasper Visualize environment have been added to the the Indago Debug Analyzer:

• Highlight Relevant Logic: This highlights the “cone of influence,” or the logic that is involved in reaching a given point
• Why: This button highlights the immediate causes for a given event, and allows users to trace backwards in time

 

More formal capabilities will come with the Indago Advanced Debug Analyzer app, scheduled for release towards the end of 2015. This includes Quiet Trace, a Jasper capability that reduces trace activity to transactions relevant to an event. Also, a what-if analysis allows on-the-fly trace editing and recalculation to explore effects and sensitivities, without having to re-compile and re-execute the simulation.

Finally, Cadence has a Superlint flow that is now fully integrated with the JasperGold Visualize debugger. This two-tiered flow includes a basic lint capability as well as automated formal analysis based on the JasperGold Structural Property Synthesis app. “This could be a very good entry point for designers to start using formal,” Hardee said.

“Formal is taking off,” Hardee concluded. “People are no longer talking about return on investment for formal—they have established that. Now they’re supporting a proliferation of formal in their companies such that a wider set of people experience the benefit from that proven return on investment.”

Further information is available at the JasperGold Formal Verification Platform (Apps) page.

Richard Goering

Related Blog Posts

- JUG Keynote—How Jasper Formal Verification Technology Fits into the Cadence Flow

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- Q&A: An R&D Perspective on Formal Verification—Past, Present and Future