General Description: If a .ngd or .ucf file contain a period constraint written
using the following syntax they are not picked up by the Constraint Editor.
NET CLK PERIOD = 30 ns;
Use the following syntax to resolve this issue:
NET "CLK" TNM_NET = "CLK"
TIMESPEC "CLK" = PERIOD "CLK" 30 ns;
This syntax will be picked up by the Constraint Editor.