UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 18591

6.1i Spartan-IIE PAR - Router unable to route all BLKRAM CLK loads with low skew resource

Description

Keywords: Spartan-IIE, clock, routing, skew, BRAM, BLKRAM

Urgency: Standard

General Description:
A case has been seen where low skew resources were not used efficiently to route a clock net with a mixture of slice and Block RAM loads. A USELOWSKEWLINES constraint had been set.

"WARNING:Guide:224 -
The following Clock signals have USELOWSKEWLINES constraint
specified. The router was not able to completely route using
the LOW SKEW resources. Check the timing report to verify the
delay and skew for this net."

Solution

This problem has been fixed in the latest 6.1i Service Pack available at:
http://support.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is 6.1i Service Pack 3.

A routing template was added to address this problem. The following environment variable needs to be set to enable this change:

Solaris and Linux
setenv XIL_ROUTE_USELOWSKEW_SLOWBLKRAM 1

Windows
SET XIL_ROUTE_USELOWSKEW_SLOWBLKRAM=1

For more general information about setting ISE environment variables, see (Xilinx Answer 11630).
AR# 18591
Date Created 09/03/2007
Last Updated 10/23/2008
Status Archive
Type General Article