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AR# 43637

Virtex-6 LXT: How to resolve "ERROR:Place:1131 - Unroutable Placement!"


I am receiving the below error message:

ERROR:Place:1131 - Unroutable Placement! A cascaded BUFGCTRL clock component

pair have been found that are not placed at a routable site pair.

The driverBUFGCTRL component <user_clock/clkout2_buf> is placed at site<BUFGCTRL_X0Y0>.

The load BUFGCTRL component<U_FUSB300/U_FUSB300_CLKRST/aux_clk_bufg> is placed at site<BUFGCTRL_X0Y31>.

The BUFGCTRL components can use the fast path between them

if they are placed in adjacent BUFGCTRL sites, and both are in the samehalf of the device (TOP or BOTTOM).

You may want to analyze why this problemexists and correct it.

This placement is UNROUTABLE in PAR and therefore,this error condition should be fixed in your design.

You may use theCLOCK_DEDICATED_ROUTE constraint in the .ucf file to demote this message to

a WARNING in order to generate an NCD file. This NCD file can then be used

in FPGA Editor to debug the problem. A list of all the COMP.PINS used in

this clock placement rule is listed below. These examples can be used

directly in the .ucf file to demote this ERROR to a WARNING.

ERROR:Pack:1654 - The timing-driven placement phase encountered an error.


This error occurs when two cascaded BUFGS are not placed in adjacent sites.
As a result, the route is not the optimal path and is not the fastest available.
You can eliminate the error and run through the project to the end without downgrading the error to a warning by using CLOCK_DEDICATED_ROUTE in the constraints.


add the constraint below in the UCF file:
INST <U_FUSB300/U_FUSB300_CLKRST/aux_clk_bufg> loc= BUFGCTRL_X0Y0
INST < user_clock/clkout2_buf > loc= BUFGCTRL_X0Y1
This constrains the placement of the two clocks and forces them to be placed in adjacent sites.
Once this is added and you run the project, the error will no longer appear.

AR# 43637
Date Created 08/15/2011
Last Updated 03/24/2015
Status Active
Type Error Message
  • Virtex-6 LXT
  • ISE Design Suite - 13.1
  • ISE Design Suite - 13
  • ISE Design Suite - 13.2