Answers Database
Long Runtimes for Some Designs
Record #1869
Problem Title:
Long Runtimes for Some Designs
Problem Description:
Platform(s): All
Architecture(s): All
Design Step(s): TRCE, PAR
Reference Number: 13236
XACT Performance may require very long runtimes to analyze some
designs.
Solution 1:
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_PATHLIM
IT variable to a low number reduces the number of paths analyzed, and consequently reduces the runti
me needed to run TRCE, ITA_FPGA, and PAR. When using this environment variable, a message is display
ed 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
analysis.
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 corre
ct 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 contain
s 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.
End of Record #1869 - Last Modified: 06/02/97 14:14 |
