Novas Verdi Helps Navigate Unfamiliar Territory to Achieve IC Design Harmony:  From 1st Hire to 1st Tapeout in 8 Months

Background

D2Audio a start-up company based in Austin, Texas develops Class-D Intelligent digital amplifiers for manufacturers of audio systems. These multi-channel amplifier "modules" are used in consumer, professional, commercial and automotive audio systems to improve sound quality, decrease heat, increase power levels, and improve the aesthetics and size of their end products. The self-contained modules provide all the benefits digital IC technology brings - smaller footprints, cooler operating characteristics, and more efficient manufacturability - while addressing the traditional challenges of using digital techniques for amplification, namely sound quality and the ability to surpass the 50-watt performance barrier.

"What really impresses everyone, from the most technical audiophile to the average consumer, is the quality of sound our system can produce. It eliminates any doubt that digital technology can be used for world class audio amplification," says Joel Page, IC Design Manager at D2Audio.

D2Audio laid out aggressive product development schedules, even before it had obtained funding. This required the most efficient use of internal resources, a sharp focus on its own core competencies, and a willingness to outsource and/or purchase anything that was not central to its value-add.

From an IC design standpoint, D2Audio faced challenges common to the industry that make design reuse and third-party IP acquisition a must. At start-up, engineering resources were limited, time-to-market requirements were demanding, and its IC design was extremely complex. Design strategies which cut design time and allow efficient enhancements in product functionality were key to success. But extensive use of external off-the-shelf IP components introduces verification challenges, particularly when trying to find the causes of errors.

A mix of technology to create a complete solution

At the heart of the D2Audio Intelligent Digital Amplifier module is D2Audios unique advantage, a pulse width modulator controller, and its accompanying firmware, giving the system its ability to process sound and perform "intelligently" in different packaging and under various environmental conditions. This is where Joel Page and his team focused the majority of their creative design time, but the complete system, packaged as a 0.18 micron IC, required many other peripheral functions as well. This included a high-performance DSP core, memory blocks, and basic analog support circuitry such as PLLs and oscillator circuitry.

"We could not afford to develop everything from scratch," explains Page. "We focused on designing the IP that makes our products unique and better, and purchased the other necessary components."

Page and his team started their IC design at an architectural level and created a high-level model to do a fundamental analysis of the system. They then went right to creating a synthesizeable model in Verilog, skipping a true behavioral modeling step because of the large amount of imported IP. But, its was still critical that the design team understood the behavior of all the IP they imported, and were able to pinpoint causes of errors.

"We needed an immediate understanding of why things were happening. Our goal was to get through the integration portion of the process quickly. However, despite the promise of quick re-use of IP, it doesnt always work out that way."

Finding the errors in unfamiliar design blocks isnt always straightforward. The way engineers debug designs is typically a very manual process of correlating logic with simulation results to infer behavior from structural information. They trace back through a design signal-by-signal and driver-by-driver. They still must determine which paths actually lead back to the root cause of specific behavior. This forces them to create a mental image of cause and effect by looking at many individual pieces of information in order to correlate the observed behavior with the design structures that produced it.

This approach doesnt reveal anything about the designs behavior over time, and lacks contextual information critical to understanding why the design block doesnt work within the system as intended. To truly figure out how a design works or why it does not, an engineer must understand perfectly how the logic of a design transforms control and datapath values over time.

Recognizing the need for design understanding from the start

The D2Audio design team recognized from the beginning that the use of third-party IP would require a new methodology for verification. Past experiences with design re-use had taught them to expect the unexpected in terms of the quality, documentation and testability of components they hadnt worked on themselves. Most importantly, they knew they would need a way to understand someone elses work.

"Our design teams collective experience with IP purchases was mixed. I knew with the type of approach we were taking here, we needed a different verification and debug methodology from the start. We were doing something fundamentally different and we had to think differently to be successful."

To help them navigate through the unfamiliar territory that design re-use presented, Page and his team turned to Novas and its VerdiÔ Automated Debug System. Unlike traditional debug tools, Verdi provides a way for engineers to locate and correct errors quickly, even in portions of the design of which they have no prior knowledge. Based on its unique Design Knowledge Architecture, the Novas system connects the design knowledge extracted from HDL source code with the verification knowledge captured from other error detecting tools such as simulators or timing analyzers.

A key aspect of Verdis approach is the way it automates tracing of sequential design behavior over multiple clock cycles to reduce debug time. The D2Audio team made extensive use of Verdis ability to perform state tracing, or the chasing of signals back through logic. "This is historically a very manual process," Page notes. "With Verdi, it was really just point and click to trace a problem, and we saw tremendous efficiency in our speed in resolving design errors."

Pages team encountered several functional errors in how state machines were being executed in a portion of the design. Verdi helped them go quickly through a state analysis, tracking the problem down to an interface error with the imported blocks support for a required standard. "There were a fair amount of registers to go through, and Verdi really showed its effectiveness in helping us find errors in designs we were completely unfamiliar with."

Colleague Mike Kost appreciates Verdis intuitive visualization and symbolic design exploration capabilities. Verdi uses sophisticated data models and exploration tools to show a map of design behavior over time, which help streamline his job: "I was new to Verdi . I was surprised by how much easier it was compared to other methods I have used in the past to track functional failures in the testbench back to the RTL causing the problem. The temporal flow view allowed me to track the meaningful signals back to the root cause of the failure."

This was especially helpful since the D2Audio team often found itself debugging functional tests on purchased IP. Verdi provided an intuitive mechanism that allowed them to use their knowledge of what the IP block should be doing at a high level and navigate through both the source RTL and the waveform dump.

Further insight into unfamiliar design elements proved helpful as well. "The most useful feature was the Trace X command that allowed me to determine where unknown conditions were entering the simulation. This shortened debugging time by hours," adds Kost.

The team also liked the way Verdi integrates seamlessly into D2Audios verification environment, which includes a varied set of tool types from multiple vendors. As a result, the D2Audio designers were able to further improve productivity by using Verdi as a control point for the design process.

D2Audio is a fabless company and uses third-party partners for back-end portions of the design process such as floorplanning, place-and-route and timing closure. They were impressed with Verdis benefit at the post-timing analysis stage when they needed to track down timing errors. By using Verdi with the floor plan and timing analysis results D2Audio received from their design services partner, "any issues we had were found effectively with Verdi," says D2Audios Kost.

Understanding design behavior essential for todays IC design

With the increasing use of imported and other types of unfamiliar IP in todays complex ICs, design teams like D2Audio need more automated ways to navigate designs and understand how design elements are supposed to work and why they dont. Verdis behavior-based approach is the key to unlocking information and imparting new levels of understanding to streamline the debug process.

As a result, D2Audio was able to tape out its first silicon within 8 months of hiring its first engineers, an impressive schedule that was essential to its business plan.

"Verdi was pivotal in accomplishing our design goals. It was a tool that we had to have. It wasnt an option," says Page. "We could have found all the errors given enough time. But, with Verdi we came to resolution very quickly, which helped us stay on schedule."

 

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