When I use a BUFGMUX in my design, the select line is not analyzed for setup/hold time with respect to both the clock inputs. Why is the offset on this signal only analyzed against one clock in the constraint detailed path and data sheet?
The analysis of the select line with respect to both clock inputs is currently not supported in TRCE/Timing Analyzer. However, the select line will be analyzed by one of the OFFSET constraints, with the usual constraint priority resolution. Most commonly, the last OFFSET constraint in the .pcf file will have the priority.
One possible way to work around this issue is to turn off the higher priority constraint and regenerate the timing report. To reanalyze the design without the higher priority constraint in Timing Analyzer, use the Analyze-> Against Timing Constraints command, uncheck the constraint that contained the select path in the last analysis, and click "OK".