I synthesize my design using Synplify. I have a PERIOD constraint for an input clock in the UCF file. When I run the Translate process, the following warning is shown in the ISE transcript window and Translate report:
WARNING:NgdBuild:1011 - The constraint <TIMESPEC "TS_rd_clk" = PERIOD "rd_clk" 2.5 ns HIGH 50 %;>[./my_constraints.ucf(5)] is overridden by the constraint <TIMESPEC TS_rd_clk = PERIOD "rd_clk" 2549.000000000 pS HIGH 50....>.
Why are the constraints in my UCF file being overridden by a different PERIOD constraint?
This is a known issue which will be resolved in a future ISE release.
By default, Synplify generates a constraint file (.NCF) with auto-generated constraints that might constrain nets already covered in the UCF file. It is expected that NGDBuild should assign higher precedence to the constraints contained in the UCF file over those listed in the vendor constraints file (NCF). However, this is not occurring in 10.1.
To work around this issue, apply the following environment variable:
For information on setting environment variables, refer to (Xilinx Answer 11630).