Answers Database

SYNOPSYS/ XC3000/XC4000: How to force insertion of a BUFGP at a clock pad.


Record #548

Product Family:  Software

Product Line:  Synopsys

Problem Title:
SYNOPSYS/ XC3000/XC4000: How to force insertion of a BUFGP at a clock
pad.



Problem Description:
Synopsys may remove a BUFGP that a user has instantiated and  replace it with a
BUFGS.
This may cause XNFPREP to issue an error if the user has also constrained that
particular clock pad to a specific BUFGP pad location.






Solution 1:

 Unless the user specifically applies a "dont_touch" attribute	on the BUFGP, th
e Synopsys compiler may replace it with a  BUFGS.

The easiest way to ensure that the Synopsys Compiler inserts a BUFGP at a clock
pad is to execute the following command either in the script file or at the
command line in the command window:


 		  set_pad_type -exact BUFGP_F <clock-pad-name>


		  Replace <clock-pad-name> with the actual name of your clock
		  pad.

The above set_pad_type command should be executed before the compile
of your design.

OR:

Instantiate a BUFGP_F and set a 'dont_touch' attribute on it before
and after compiling the code. To set a dont_touch attribute,
execute the following command either in the script file or at the
command line in the command window:

		 set_dont_touch "U2"
				

Replace U2 with the actual label of the instantiated BUFGP_F.




End of Record #548