AR# 3136


How does the XILINX_PATHLIMIT environment variable work?


General Description:

Sometimes long runtimes are experienced, and could be because there are many

paths to analyze. Users may also get a message during par such as the


WARNING:xiltw:1 - The current connection evaluation limit of 1000 caused the

truncation of timing analysis for paths through 2.20% of your constrained

connections, which may limit the accuracy of this analysis. You may

specify a larger limit with the XILINX_PATHLIMIT environment variable to

increase the accuracy of this analysis.

So the user may want to use this XILINX_PATHLIMIT, but are unsure how it is

going to affect the results.


The XILINX_PATHLIMIT will limit the number of path evaluations per connection

to the specified limit. So the specified number will run a n# depth-first

search passes through each connection (for each constraint), consequently

limiting the total number of overall paths analyzed for the design, and

possibly reducing runtime.

Using this environment variable does NOT guarantee that the worst-case path

is analyzed. The paths it picks is not random, but also it will not guarantee

that the worst case path is analyzed. So using this environment variable could

be risky if expecting to get full timing coverage on the design. So down the

road this could lead to timing errors. So to get a faster evaluation on the

design this environment variable could be used, but later it would be a good

idea to re-run TRCE without the XILINX_PATHLIMIT, to ensure that no timing

errors remain.

AR# 3136
Date 01/18/2010
Status Archive
Type General Article
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