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# 38751

12.3 XST-2: New parser does not accept "syn_preserve = 1" as a valid setting


I am receiving the following Warning Messages in ISE Design Suite:

WARNING:Xst:3149 - Value "1" of property "syn_preserve" is not applicable.
WARNING:Xst:3149 - Value "1" of property "syn_preserve" is not applicable.


These warnings occur with the new XST parser for Virtex-6, Spartan-6, and later architectures.

The reason is that the attribute "syn_preserve" is being set to 1 as outlined in the Synplify user documentation.

/* synthesis syn_preserve=1 */;

To workaround the warning and to correctly apply the constraint, use the following:

/* synthesis syn_preserve=TRUE */;

This issue is fixed in the 14.1 release.

The following message is generated instead:

WARNING:Xst - Value "1" of property "syn_preserve" is not applicable. List of valid values is "true, false, yes, no"

AR# 38751
Date Created 10/25/2010
Last Updated 09/24/2014
Status Active
Type General Article
  • ISE Design Suite - 12.3
  • ISE Design Suite - 12.1
  • ISE Design Suite - 12.2