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You can control PALACE operations in<br />

the standard flow by a simple four-level<br />

effort option.<br />

The effort level determines how aggressively<br />

the PALACE tool will try to optimize<br />

your design, with the first level optimizing<br />

for minimum area utilization and the<br />

remaining levels optimizing for maximum<br />

performance. The default level is the third<br />

level, and it is the initial recommended<br />

level when performance is an issue.<br />

After specifying the effort level, no further<br />

user intervention is required. Using<br />

PALACE technology in this flow provides<br />

you with the advantages of physical synthesis<br />

in a simple push-button automated<br />

flow, and can meet most realistic design<br />

requirements.<br />

Guided Flow<br />

You can use the PALACE tool in the guided<br />

flow for Virtex-II devices to achieve the<br />

incremental improvements needed to<br />

meet your design requirements. In this<br />

flow, you first generate an NCD (native<br />

circuit description) file by placing and<br />

routing your design. This NCD file is<br />

then converted to XDL (<strong>Xilinx</strong> Design<br />

Language) format with the <strong>Xilinx</strong> XDL<br />

utility and passed as an input to the<br />

PALACE program, along with the design<br />

constraint file. The PALACE tool optimizes<br />

the paths that do not meet timing<br />

requirements to help you achieve timing<br />

closure. As with the standard flow, an<br />

optimized netlist and constraint file is<br />

produced that you use in the rest of your<br />

design flow.<br />

You can control PALACE operation in<br />

the guided flow by a simple two-level effort<br />

Category (Design) Spartan-3 Device<br />

option, which determines how aggressively<br />

the PALACE program will try to optimize<br />

your design. As with the standard flow, no<br />

further user intervention is required. Using<br />

PALACE physical synthesis in the guided<br />

flow provides you with the capabilities of<br />

an advanced physical synthesis solution in<br />

a simple push-button automated flow.<br />

Thus, you can meet the “last mile” performance<br />

requirements of your design.<br />

Achieving Best Results with PALACE<br />

Effective use of the PALACE physical synthesis<br />

solution can help you meet your<br />

design requirements quickly. With the<br />

standard and guided flows, you have two<br />

simple but powerful solutions that should<br />

be used together in order to achieve the<br />

best results.<br />

When you use the PALACE engine in<br />

either flow, you should always include timing<br />

constraints in the input constraint file.<br />

Meaningful and accurate timing constraints<br />

are important because they help the<br />

PALACE program to focus on the problem<br />

areas of your design, while allowing tradeoffs<br />

with other non-critical areas.<br />

If you are particularly concerned about<br />

area utilization, you should use the first<br />

effort level on your initial run. Otherwise,<br />

you should use the default settings, which<br />

will automatically run PALACE physical<br />

synthesis in standard flow at a highoptimization<br />

effort level.<br />

After you have obtained the optimized<br />

results, you can analyze either the<br />

PALACE report file or the report from an<br />

implementation run to determine if the<br />

result meets your requirements. If you miss<br />

your timing targets by a wide margin<br />

Performance Gain<br />

(% Max Frequency)<br />

DSP (DES) XC3S400FT256-4 37%<br />

Microcontrollers (uP1232a) XC3S200FT256-4 28%<br />

Communications (Reed-Solomon decoder) XC3S200PQ408-4 8%<br />

Bus Interfaces (I 2 C Master) XC3S50PQ208-4 12%<br />

State Machine and Control Logic (Arbiter) XC3S400FT256-4 93%<br />

Table 1 – Examples of PALACE performance improvements<br />

(more than a few nanoseconds in Spartan-<br />

3 devices), you should try running the<br />

PALACE engine in the standard flow with<br />

a higher effort level. If you are using a<br />

Virtex-II device and have still not met<br />

timing requirements, you should try the<br />

guided flow to achieve the last nanosecond<br />

or so of required performance.<br />

The performance gains that you obtain<br />

with PALACE physical synthesis will vary<br />

depending on the type and complexity of<br />

the design. Table 1 shows performance<br />

improvements obtained when the PALACE<br />

solution was used in the standard flow for a<br />

few sample designs from a variety of categories.<br />

In all of these cases, the design flow<br />

was identical for two runs, except that the<br />

PALACE solution was used before the<br />

implementation stage in the second run. As<br />

you can see, PALACE physical synthesis<br />

provides a substantial increase in performance<br />

that allows you to move to a slower<br />

speed grade in many cases.<br />

Conclusion<br />

As FPGAs continue to increase in density<br />

and complexity, you need to ensure that<br />

your tools extract the maximum potential of<br />

the device’s architecture in the minimum<br />

amount of time. This is especially true for<br />

cost-sensitive design cycles that involve the<br />

low-cost Spartan-3 FPGAs. Without a physical<br />

synthesis solution that can effectively<br />

exploit the architecture of your target device,<br />

you risk overrunning your forecasted costs<br />

by having to move to a more expensive part,<br />

or by spending too many engineering hours<br />

trying to achieve timing closure.<br />

The Aplus PALACE tool is an<br />

advanced physical synthesis solution that<br />

fits seamlessly within your existing design<br />

flow for all <strong>Xilinx</strong> Spartan-II, Spartan-IIE,<br />

Spartan-3, Virtex, Virtex-E, Virtex-II, and<br />

Virtex-II Pro FPGAs, providing you<br />

with a fully automated solution to help<br />

achieve your design requirements in the<br />

minimum amount of time. In fact, you<br />

may even be able to move to a smaller part<br />

or a slower speed grade and dramatically<br />

reduce your costs.<br />

To learn more about the PALACE physical<br />

synthesis tool, e-mail info@aplusdt.com<br />

or visit www.aplus-dt.com.<br />

Fall 2003 Xcell Journal 13

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