Why am I seeing a change in Tbxcy when moving to 10.1 SP3?
Tbxcy is any path from BX to COUT. In addition to there being several different paths from BX to COUT that can cause several different values for Tbxcy to be reported, there are also some changes to the way the timing tools will handle these calculations in Service Pack 3 for 10.1.
Prior to Service Pack 3 for 10.1, the tools were overreporting BX to COUT.
After Service Pack 3 for 10.1, the tools will report more accurate results that allow designs to operate at higher performance.