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AR# 36138

14.x Timing Analysis - The skew calculation is wrong when applying a MAXSKEW constraint

Description

The skew calculation for my MAXSKEW constraint shows that the delay is the same for each of the paths, but the skew actually has a value:

==============================================

Timing constraint: NET "module/my_net" MAXSKEW = 0.01 ns;
1 net analyzed, 1 failing net detected.
1 timing error detected.
Maximum net skew is 0.085ns.

--------------------------------------------------------------------------------

Slack: -0.075nsmodule/my_net
Report: 0.085ns skew fails 0.010ns timing constraint by -0.075ns
From To Delay(ns) Skew(ns)
ILOGIC_X2Y181.O BUFR_X2Y8.I 0.141 0.085
ILOGIC_X2Y181.O BUFIODQS_X2Y18.I 0.141 0.085

--------------------------------------------------------------------------------

What is wrong with TRCE and how do I correct this problem?

Solution

4:14TRCE is reporting the MAX values to the MIN (or Relative MIN) values.The Delay that is reported is the MAX and this MAX can be the same, however, the skew calculation uses a combination of MAX and[Relative] MIN as follows:

SKEWhold = Max(DST clock delay)- Min(SRC clock delay)
SKEWsetup = Min(DST clock delay)- Max(SRC clock delay)

Linked Answer Records

Associated Answer Records

AR# 36138
Date Created 10/07/2011
Last Updated 12/15/2012
Status Active
Type General Article
Tools
  • ISE Design Suite - 11.1
  • ISE Design Suite - 11.2
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  • ISE Design Suite - 12.1
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  • ISE Design Suite - 13
  • ISE Design Suite - 13.1
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