General Description: An internal constant used in the representation of delay values
conflicts with real negative delay values, causing TRCE to ignore real delay values.
In particular, negative hold times of -0.001ns will not be reported (and race
checking will not be performed on these delays).
In virtex it is possible of getting -1ps hold times causing the tools to
ignoring them. Because the tools thought these were invalid delays,
no hold checking was performed when this occured.
Currently there is no resolution to this issue.
This is fixed in the next release of the software, version 2.1i