AR# 1869


Long Runtimes for Some Designs


Platform(s): All

Architecture(s): All

Design Step(s): TRCE, PAR

Reference Number: 13236

XACT Performance may require very long runtimes to analyze some



Workaround: Runtime can now be controlled using the

XILINX_PATHLIMIT environment variable, which limits the number

of connection evaluations per timing constraint to the specified number. Setting the XILINX_PATHLIMIT variable to a low number reduces the number of paths analyzed, and consequently reduces the runtime needed to run TRCE, ITA_FPGA, and PAR. When using this environment variable, a message is displayed indicating that analysis has been truncated. Following is a sample message:

WARNING:0 - The current connection evaluation limit of

1000 caused the truncation of timing analysis for

paths through 2.88% of constrained connections, which

may limit the accuracy of this analysis. You can

specify a larger limit with the XILINX_PATHLIMIT

environment variable to increase the accuracy of this


This message indicates the percentage of design connections where analysis was truncated in order to reduce overall runtime. If this message appears, analysis is incomplete and may not guarantee correct timing results. You are encouraged to use the largest limit possible that provides an acceptable runtime in order to ensure the most accurate timing analysis possible.The timing report also contains a list of design connections where analysis was truncated, and you should check these against the reported critical path(s) to help determine if irrelevant paths are being analyzed by the tools. In some cases, long runtimes may result from large groupings used in the FROM:TO type of TIMESPECs. In these cases, runtimes can be improved in these ways:

Specify a PERIOD TIMESPEC that includes the majority of the

paths to be analyzed (for example, TIMEGRP "ALL_FFS"

PERIOD = 30), and use the FROM:TO TIMESPECs only for smaller groups of multicycle paths not included in the global PERIOD TIMESPEC.

When possible, use a MAXDELAY TO: constraint instead of a

MAXDELAY TO:FROM constraint.
AR# 1869
日期 12/11/2011
状态 Archive
Type 综合文章
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