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AR# 23640

8.2i Virtex-5 PAR - Performance Evaluation Mode leads to unrouted design due to over constraining

Description

I have noticed that my design is unroutable when I tell PAR to ignore my timing constraints (-x), but it runs okay if I do not. Wouldn't it normally be more difficult to both satisfy timing constraints and route a design, than to just route it? 

 

This option is referred to as Performance Evaluation Mode and involves the automatic constraint of all clocks. Several cases have been seen where this automatic constraining process over-constrains the design, which can lead to routing failures. 

 

If the goal is to disable timing driven operation entirely, the hidden PAR switch "-ntd" can be used instead.

Solution

This problem has been fixed in the latest 8.2i Service Pack available at: 

<http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp>
The first service pack containing the fix is 8.2i Service Pack 1.

AR# 23640
Date Created 10/22/2008
Last Updated 05/20/2014
Status Archive
Type General Article