ID:177004 Fitter encountered congestion while routing the <type (including space if not blank)>PLL feedback clock for <name>

CAUSE: The Fitter encountered congestion on the specified Phase-Locked Loop (PLL) feedback path. The feedback path required by the PLL could not be used because some of the routing resources were used for another connection. The type of feedback path required to properly compensate this PLL clock depends on the type of network driven by the PLL clock (Global or Regional), as well as 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. This message indicates congestion either on the path to the clock network, or on the return path from the clock network to the PLL.

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. Alternatively, attempt to lower the clock network usage in your design, either by using fewer clocks, or by using smaller clocks instead of larger ones (for example, using regional clocks instead of a global clock where possible). You can also try to route a different feedback path type for the PLL. The feedback path type can be manually overridden using the PLL_FEEDBACK_CLOCK_SIGNAL assignment. Note that overriding the return path automatically chosen by the Fitter may be suboptimal for timing. If the PLL is fed directly by a clock pin, the far path should be used to account for the longer delay reaching the PLL. 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. If the return path (near or far) is unspecified, the Fitter will attempt to use the path that is optimal for timing. If possible, try using direct compensation mode, which does not use any clock network resources.