ID:12392 Feedback return path used by PLL(s) in location <name> is not of the recommended type

CAUSE: The recommended return path could not be routed for the Phase-Locked Loop (PLL) feedback signal. A path of the recommended type may not exist at the location, nodes along the path may be used or reserved by another signal, or the path type may be manually specified by an assignment. The feedback path recommended to optimally compensate this PLL clock depends on the PLL source. PLLs far from clock pins usually have multiple compensation return paths available - the source and placement of the PLL input clock signal determines whether a near (shorter) or far (longer) return path should be used. If the PLL is fed directly by a dedicated clock pin, the PLL should use the far return path to compensate for the added delay to the PLL, otherwise the near path should be routed for optimal timing. PLLs close to dedicated clock pins (top or bottom) have only one return path. Due to the lower clock pin to PLL delay, the path can satisfy both near and far compensation delay requirements. Using a suboptimal return path may affect timing closure in certain cases.

ACTION: If the PLL is locked to a specific location, try unlocking the PLL to allow the Fitter to try different locations, because different locations can use different parts of the clock network for its feedback. The feedback path type can be manually specified as a hard constraint with the PLL_FEEDBACK_CLOCK_SIGNAL assignment. Possible values for the feedback path type are: Global Clock, Regional Clock, Far Global Clock, Far Regional Clock, Near Global Clock, and Near Regional Clock.