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AR# 12689

4.1i Virtex-II - Device file changes in 4.1i may invalidate some routing in 3.1i Virtex-II NCD files

Description

Keywords: Ncd:69, saved, routing, load, loaded, old, NCD, existing

Urgency: Hot

General Description:
NCD files that were routed by version 3.1i may report the following warning messages when loaded by any 4.1i application (PAR, FPGA Editor, DRC, NCDREAD):

"WARNING:Ncd:69 - The saved routing information for the current signal from (-8647, -70272) to (-6527, -69888) cannot be located. This information will be lost."

"WARNING:Ncd:73 - The signal "grstcnt" has lost all route information due to possible device changes. The signal will now be considered completely unrouted."

"WARNING:Ncd:69 - The saved routing information for the current signal from (-8647, -70288) to (-10467, -69880) cannot be located. This information will be lost."

Solution

This message is an indication that the signal mentioned ("grstcnt" in this case) made use of a routing resource that was valid in a previous revision of the device data files, but is invalid in the new device data files. In this case, the device data files were not utilizing all available routing resources in version 3.1i and were modified to improve routability in 4.1i.

Q: What designs are potentially affected?
A: All Virtex-II designs routed in version 3.1i.

Q: Does this mean that my 3.1i NCD and bit files are bad?
A: No, the 3.1i NCD was valid in a 3.1i environment. The affected signal simply needs to be re-routed in 4.1i.

Q: How can I easily check my existing designs for this problem?
A: Any 4.1i Xilinx implementation tool that loads NCD files can be used to detect this problem. From the command line, the easiest check is "drc orig.ncd". From the GUI, FPGA Editor can be used.

To correct this problem, the affected signal can be re-routed at the new revision level. A re-entrant route will accomplish this most efficiently:

par -k orig.ncd new.ncd orig.pcf
AR# 12689
Date Created 08/29/2007
Last Updated 10/23/2008
Status Archive
Type General Article