Design Compiler Graphical

Overview
Continuing the trend of delivering innovative synthesis technology, Design Compiler® Graphical streamlines the flow for a faster, more predictable design implementation. As geometries shrink to 65nm and smaller process technologies, design complexities increase multifold, making it extremely difficult for designers to complete projects on schedule. Nanometer effects such as coupling capacitances between parallel interconnects have much higher impact on interconnect delays and need to be considered during synthesis to ensure predictable design implementation. Moreover, routing congestion, whether caused by the floorplan or the presence of highlyinterconnected logic structures in the netlist, needs to be fixed early in the design cycle to avoid iterations. RTL synthesis that produces a better starting point for physical implementation improves schedule predictability and avoids costly iterations between synthesis and place-and-route.

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Design Compiler Graphical extends DC Ultra™ topographical technology to produce physical guidance to the IC Compiler place-and-route solution, tightening timing and area correlation to 5% while speeding-up IC Compiler placement by 1.5X. It also applies additional physical optimization techniques and considers smallgeometry effects such as coupling capacitances for accurate delay modeling. RTL designers gain access to IC Compiler’s design planning capabilities from inside the synthesis environment. With the push of a button, they can perform what-if floorplan exploration to identify and fix floorplan issues early and achieve an optimal floorplan efficiently. In addition, Design Compiler Graphical predicts circuit congestion “hot spots,” providing designers with visualization of congested circuit regions, and performs specialized synthesis optimizations to minimize congestion in these areas. This enables RTL designers to avoid wire-routing congestion problems that occur during detailed routing. To accelerate synthesis, Design Compiler Graphical also includes scalable multicore infrastructure that delivers significant runtime speed-up on multicore compute servers, yielding 2X faster runtimes on four cores.

Today’s complex designs need to operate under multiple conditions and in many modes such as scan, sleep and other functional modes. Optimizing serially across each mode and several operating conditions (corners) can be time-consuming and require multiple iterations to achieve optimal results. With Design Compiler Graphical, RTL designers can analyze and optimize designs across multiple modes and corners concurrently to substantially drive down design development time and cost.

Figure 1: Design Compiler Graphical

Key Benefits

Physical Guidance to IC Compiler
With designs becoming more complex along with shrinking geometries, designers require even tighter correlation between synthesis and layout results. Additionally, as geometries become smaller, the coupling capacitance between adjacent parallel wires is much higher due to the fact that spacing between wires is smaller and the relative heights of the wires are greater. Hence, the impact of coupling capacitance is much higher on design delays and needs to be accounted for in synthesis.

Design Compiler Graphical extends topographical technology in DC Ultra to create physical guidance for IC compiler, streamlining the implementation flow and accelerating IC Compiler placement runtimes by 1.5X. Physical optimizations during synthesis create a better starting for physical implementation and accurately model small-geometry effects such as coupling capacitance,bringing synthesis timing and area results to within 5% of layout.

Figure 2: Timing correlation

Figure 3: Area correlation

Figures 2 and 3 illustrate improvements in timing and area correlation, respectively, across multiple designs using physical guidance. On the X-axis are the designs and the Y-axis is % delta between synthesis and layout results. The light purple bars (on the left) show the delta between synthesis and layout without passing physical guidance. The purple bars show the delta for the same designs with physical guidance technology. As shown in these figures, results are consistently within 5% when physical guidance is passed from Design Compiler Graphical to IC Compiler. Figure 4 shows placement runtime improvements using physical guidance technology. On the X-axis are the designs and on the Y-axis are the runtimes in hours. The light purple bars represent IC Compiler placement runtime without physical guidance and the purple bars represent IC Compiler placement runtime with physical guidance. As illustrated by the figure IC Compiler placement runtime is much faster when physical guidance is passed from Design Compiler Graphical, averaging 1.5X faster.

Figure 4: IC Compiler placement runtime

Accurate Congestion Prediction and Congestion- Driven Optimization in Synthesis
Routing congestion occurs when the resources (tracks) needed to route a design exceed the available resources. With more functionality crowded onto a chip, congestion makes it difficult to route designs. During place-and-route designers deploy various techniques to alleviate congestion. These techniques can include changes to the floorplan such as port or macro locations, changing target gate utilization, adding placement blockages, etc. Making such changes during place and route is time consuming and can lead to schedule delays. Furthermore, these techniques may not work and the designer may be required to iterate back to the RTL and recode the RTL source to remove congestion-causing design characteristics. These options are not optimal and can lead to missed schedules, missed design goals and result in added costs.

Design Compiler Graphical includes Synopsys’ virtual global-routing technology that enables designers to predict wire-routing congestion during RTL synthesis. This technology allows designers to identify and fix design issues to reduce routing congestion, eliminating costly iterations between synthesis and physical implementation to achieve their design goals and speed up place and route.

Figure 5A shows a congestion map as predicted by Design Compiler Graphical. The color distribution of the map indicates the relative routability of the design, with large concentrations of white and red indicating areas of high congestion and blue representing the least-congested areas. Figure 5B shows the congestion map in IC Compiler after optimizing the design in place and route to reduce congestion. It is clear that Design Compiler Graphical is able to identify the design’s highly congested areas during RTL synthesis, thus providing designers with valuable information on the design’s ability to route during place and route.

Figure 5: Design Compiler Graphical results

Design Compiler Graphical provides an automated way to optimize the RTL to reduce routing congestion. It performs specialized optimizations to generate a routing-friendly netlist topology that minimizes highly-congested structures and wire crossings in congested areas. By intelligently choosing netlist structures that are easier to route, Design Compiler Graphical can generate a netlist that is a better starting point for physical implementation, leading to faster place and route.

Figure 6: Design Compiler Graphical and IC Compiler congestion maps

Figure 6A shows the congestion characteristics of the same design highlighted in Figure 5A. Figure 6B shows this design after optimizing it to reduce congestion using Design Compiler Graphical. It clearly shows that the congestion optimization technology has significantly reduced wire-routing congestion in synthesis, resulting in a design with minimal to no congestion as shown in Figure 6C after placement in IC Compiler. Design Compiler Graphical has automatically optimized this design to minimize wire-routing congestion by taking into consideration the congestion characteristics of the synthesized cells.

All scan compression schemes for lowering IC testing costs are susceptible to congestion because increasing the number of scan chains adds more wires between the compression logic and the scan chains. The higher the targeted compression level, the more scan chains produced and the greater the potential for congestion. Design Compiler Graphical uses several optimization methods and works with DFTMAX™ compression to minimize congestion associated with high compression.

Early Physical Visualization
Design Compiler Graphical includes a physical viewer that allows RTL designers to view layout congestion in their design during synthesis, as shown in Figure 7. Routing congestion that is related to floorplan, such as macro placement or port location, cannot be automatically optimized in synthesis. These congestion issues can only be resolved by changing the floorplan. Using Design Compiler Graphical’s physical viewer, designers can identify floorplan issues such as sub-optimal macro or port locations that are causing timing violations or congestion “hot-spots” and use the push-button floorplanning capability described later to take corrective measures to alleviate congestion problems before place and route.

Figure 7: Interactive analysis of congestion map in Design Compiler Graphical

These interactive visualization capabilities also include the ability to cross-highlight suspect physical cells in the congestion map to the netlist, as shown in Figure 8. This allows the designer to easily isolate problem timing paths and make necessary changes during RTL synthesis.

Figure 8: Design Compiler Graphical physical view

Push-Button Floorplan Exploration for Faster Design Convergence
Traditionally, if changes to design floorplans were needed, RTL designers had to ask their counterparts on physical design teams to adjust the floorplan, resulting in iterations between the teams. With immense time-tomarket pressures, designers need a solution to reduce these iterations. Design Compiler Graphical provides RTL designers access to IC Compiler design planning capabilities from within the familiar synthesis environment. After detecting design issues, such as routing congestion or timing violations due to floorplan characteristics, RTL designers can now amend the floorplan and re-synthesize the design with an updated floorplan without ever leaving the synthesis environment. The IC Compiler design planning menus have been simplified to give RTL designers ease of use for simple floorplan modifications. An option is available for expert users to utilize the full, advanced floorplanning capabilities. The Design Compiler Graphical and IC Compiler design planning link is transparent to users hence no setup or data transfer is required. Once the designer has created an optimal floorplan, he can re-synthesize the design with the new floorplan and also save it to be used for physical implementation downstream.

Figure 9 shows an example of design layout where congestion hot spots occurred due to a very narrow channel between macros as shown in Design Compiler Graphical’s layout viewer. A click on the “Start Design Planning” menu option in Design Compiler (see Figure 10) opens a new IC Compiler design planning window with the design floorplan loaded for editing. With very few maneuvers RTL designers can move the macro to eliminate this narrow channel as shown in Figure 11. Once the floorplan edits are made, designers can save the floorplan as shown in Figure 12 and re-synthesize the design with the updated floorplan. As shown by the congestion map in Figure 13, with the updated floorplan, routing congestion has been eliminated and the design is ready for physical implementation.

Figure 9: Routing congestion identified in Design Compiler

Figure 10: Accessing IC Compiler design planning within synthesis

Figure 11: Floorplan editing to address routing congestion

Figure 12: Saving Floorplan updates

Figure 13: Congestion eliminated

Design Compiler Graphical helps RTL designers perform a what-if analysis of floorplan quickly and efficiently so that they can be ensured that the design will meet its targets during physical implementation without requiring iterations.

Multicore Infrastructure Delivering 2X Faster Runtime on 4 Cores
The advent of multicore processors in computer platforms has boosted the processing power available to designers. Design Compiler Graphical has a scalable infrastructure to take advantage of multicore compute servers. Using an optimized scheme of distributed and multithreaded parallelization, Design Compiler Graphical delivers a 2X improvement in runtime on quad-core platforms. The new infrastructure delivers runtime benefits without varying the quality of results.

Multi-Mode, Multi-Corner (MCMM) Synthesis
MCMM optimization is useful for designs that can operate in many modes such as test mode, low-power active mode, stand-by mode and so on. Used along with specification of power intent in the Unified Power Format (UPF), it serves as the key enabling technology for performing dynamic voltage and frequency scaling (DVFS) design realization.

Implementation of a design must take into account all of the different operational modes that a design can have. For example, a single block can operate in fully functional, low-power active, stand-by and/or completely shut-down modes. Without multi-mode optimization, the typical flow is to perform timing optimization sequentially for the different modes targeting various corners that represent the different operating conditions and constraints. Design Compiler Graphical’s multi-mode concurrent optimization reduces the number of iterations providing faster time to results for multi-mode designs.

One of the primary benefits of performing multi-corner optimization is to get optimal leakage results. Prior to the availability of Design Compiler Graphical MCMM optimization, designers typically optimized their designs either by performing leakage power optimization on the same corner as timing optimization, or by performing leakage and timing optimization sequentially using different corners for worst case timing and worst case leakage.

The graph below (Figure 14) shows the effects of the worst case timing and leakage corner of a 65nm low power process where the higher voltage corner (1.32V) reflects the best performance but leakage is at its worst. Conversely, the low voltage corner (0.9V) reflects the best leakage; however, performance (or speed) of the design will be at its slowest at this environmental condition. Both of these corners must be accounted for simultaneously in order to achieve the optimal leakage and performance objectives for the design.

Figure 14: Worst case leakage and timing corners

In addition, with the complexities of sub-micron processes, the worst case leakage corner is now changing from the typical hot temperature (125C) at VDD+10% case to a temperature inversion corner usually occurring at a colder temperature environment. Design Compiler Graphical’s MCMM optimization can take all of these different process corners into account to provide the best leakage results while trying to minimize impact to performance. The ability to concurrently optimize for multiple modes and corners reduces iterations between the front- and back-end implementation, allowing designers to achieve rapid design convergence.

Easy to Adopt
Design Compiler Graphical is designed for seamless integration into the current RTL synthesis use model. It uses the same setup as DC Ultra topographical technology. Similarly, it is designed for RTL designers, does not require deep physical design expertise, and improves productivity by enabling more informed decisions during RTL synthesis with early visibility into what the design characteristics will be during place and route. The inputs to Design Compiler Graphical, which are the same as DC Ultra with topographical technology, are listed below and also shown in Figure 15:

Design RTL
Logical Library (db)
Physical Library (Milkyway™)
Design constraints (SDC)
Optional physical constraints (Floorplan)

Figure 15: Design Compiler Graphical inputs and outputs

The output is a netlist optimized for timing, area, test, power and congestion with accurately-predicted layout results, ready for physical implementation hand-off. In addition, physical guidance for Synopsys place-and-route solution IC Compiler can be created, tightening timing and area correlation to 5 percent while speeding up IC Compiler’s placement phase by 1.5X.

Conclusion
Design Compiler Graphical significantly boosts RTL designers’ productivity. It provides the ability to accurately predict, visualize and alleviate routing congestion, creating an easy-toroute netlist substantially reducing iterations between synthesis and physical implementation. It enables RTL designers to perform floorplan exploration from within the synthesis environment and converge on the optimal floorplan faster. In addition, it accurately models the effects of smaller geometries, deploys advanced physical optimizations and generates physical guidance for IC Compiler place-androute solution to further tighten the correlation and accelerate physical implementation. Design Compiler Graphical is 2X faster on multicore compute servers while ensuring zero deviation of synthesis results. It also optimizes designs across multiple modes and corners concurrently to achieve optimal results faster.

Availability
Design Compiler Graphical is available as an add-on to DC Ultra.