Electronic Design
Static Timing Analyzer Addresses Corner-Case Explosion

Static Timing Analyzer Addresses Corner-Case Explosion

Static timing analysis (STA) is used throughout chip design. It’s employed for the creation of basic constraints in synthesis, for block- and chip-level timing closure in physical implementation, and for engineering change order (ECO) analysis and final timing signoff prior to physical verification and tapeout.

Despite the fact that chip complexity has since skyrocketed, the predominant architecture for STA tools was designed more than 15 years ago. At that time, the state-of-the-art process technology was 250 nm. The largest chips contained about a million instances. Most importantly, those 1997-era chips required analysis of perhaps six STA scenarios (number of operating modes times the number of PVT, or process-voltage-temperature, corners).

Contrast that with today’s 28-nm process technology, which yields chips of more than 50 million instances and over 400 STA scenarios to be run. The explosion in corner-case analysis stems from the number of operating modes, such as full power, reduced power, standby, and so on, found in today’s consumer electronics, particularly cell phones. Transitioning among these modes often means changes in chip operating voltages or clock speeds. Thus, each mode must be analyzed for timing at all PVT points.

These factors translate into numerous pain points for SVT users, most of which center around runtime and capacity issues. Another associated issue is the need to spend on larger servers and multiple licenses. With the release of its Tekton static timing analyzer, Magma Design Automation aims to address all of these issues in one fell swoop.

Centered on a next-generation architecture, Tekton is designed to more efficiently handle on-chip variation (OCV), composite current-source models, and crosstalk analysis. A key capability is its multi-mode/multi-corner (MM/MC) analysis technology, which enables users to run a large number of STA scenarios on one machine.

Tekton performs fast and accurate what-if analysis for engineering change orders. It can be used in such scenarios along with Tekton QCP, a high-capacity full-chip extraction platform that enables MC extraction with minimal increases in runtime. With the combination of Tekton and Tekton QCP, designers can change their netlist and get very quick extraction feedback on how the changes impact timing. Further, Tekton is tightly correlated to existing signoff tools. It has Magma’s FineSim Spice simulation built in as well for even more accuracy enhancement.

Extraction is an important part of any flow, but it becomes critically important in the later stages for analysis of ECO. In a traditional flow, changing the netlist results in an iterative trial-and-error loop. “The timer gives some feedback on how the changes impact timing, but it doesn’t account for layout,” says Bob Smith, vice president of product marketing within Magma’s Design Implementation Business Unit. In a flow with Tekton, because the QCP extractor runs at the same time, netlist changes are responded to with instant feedback on how timing is affected. As a result, the ECO cycle (see the figure) is less fraught with iterations and is much faster.

Magma is making a very bold claim for Tekton, which is that any design can be timed in less than one hour. One benchmark involved a design of 1 million instances, for which 12 scenarios were analyzed. With both crosstalk and on-chip variation analysis in force, this design took just 13.4 minutes of runtime. A design with 11.4 million instances ran in 41 minutes on a single-CPU machine and in just 8.8 minutes on an eight-core machine.

Why is the multiple-STA-scenario issue so important? Consider an example from a Magma customer. In this case, the design isn’t huge, with 1.3 million cells and targeted at 65 nm. The chip has three operating modes and nine PVT corners to analyze, giving the designers 27 STA scenarios to analyze. According to Smith, this led to an unwieldy analysis problem with the customer’s existing flow. “That flow, without involving crosstalk analysis, takes 65 minutes to do one run. Running all 27 scenarios means 27 runs at 65 minutes each,” Smith said. Invoking crosstalk analysis would further significantly impact runtime.

In contrast, Tekton, running on a single four-CPU machine with one license, ran all 27 scenarios in under 30 minutes with crosstalk analysis. The architecture is fully multi-threaded, resulting in orders-of-magnitude improvements in runtime without having to invest in multiple licenses or large costly servers. Magma’s benchmarks have shown that scaling is almost linear with up to 24 CPUs.

Magma Design Automation

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