When running an Unconstrained Path Report (Analyze
Against Timing Constraints - 'Report unconstrained
paths' option) in Timing Analyzer, the report includes the
timing constraints, then the Unconstrained Path Analysis.
Also See (Xilinx Solution 8072)
The unconstrained paths are listed under the keywords
'Unconstrained Path Analysis' in the Timing Analyzer.
The workaround is to run trace (TRCE) from the
command line with the following syntax:
trce -u 12 design.ncd design.pcf -o output_file.twr