Error : Illegal constraint of DLL to the region (X, Y) to (X, Y): no valid locations in region

Description

You may experience the above fitter error when compiling a UniPHY-based memory controller in the Quartus® II version 12.1. The error occurs because there are no dedicated clock routing resources between the two PLLs.

Resolution

The workaround is to insert a clock buffer (altclkctrl) between the pll_ref_clk input and the PLLs.