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AR# 12718

4.1i Virtex-II MAP - "FATAL_ERROR:Pack:pksv2slice.c:333: - Unable to create route through signal..."


Keywords: MAP, Virtex-II, related packing

Urgency: Hot

General Description:
MAP fails with the following fatal error during related packing:

"FATAL_ERROR:Pack:pksv2slice.c:333: - Unable to create route through signal. Signal Cbout[0]_rt already exists. Process will terminate. To resolve this error, please consult the Answers Database and other online resources at http://support.xilinx.com."


This problem is a regression from version 3.1i, and the failing circuit can be traced from the signal name in the error message. In all cases investigated so far, this signal is driven by a register and, among other things, drives an inverter that in turn drives a pair of LUT1s.

In turn, the LUT1s each drive a register input and MUXCY select pin. The failure appears to involve MAP merging the inverter and the LUT1s. You may work around the problem by preventing this merger; to do this, apply the following UCF constraint to the signal between the inverter and the LUT1s:

NET "sig_name" KEEP ;

This work-around does not degrade the circuit performance.

This problem is fixed in the latest 4.1i Service Pack, available at:
The first service pack containing the fix is 4.1i Service Pack 3.
AR# 12718
Date 08/20/2003
Status Archive
Type General Article