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# 9455

XST - "WARNING:Xst:37 - Unknown property 'attribute_name'." What does XST do with unknown attributes?


XST returns the following message when it encounters an attribute it does not recognize:

"WARNING:Xst:37 - Unknown property 'attribute_name'."

What does XST do with unknown attributes (or constraints) in HDL code?


All attributes can be divided into two main groups:

- Attributes that XST takes into account during the synthesis process (optimization goal, optimization effort, etc. See the "XST User Guide" for a complete list of synthesis attributes/constraints).

- Attributes that have no influence on the XST optimization and are simply propagated to the PAR via NGC. See (Xilinx Answer 8487) for information on constraints that XST does not recognize.

Regardless of the group, XST checks the name of the constraint; if it is not known, a warning message is generated and the attribute is ignored.

For constraints that XST does not recognize, the only solution is to pass the constraint through the UCF.

If the INIT_xx constraint in your XCF file is within the BEGIN/END keywords:

BEGIN model "model_name"




XST issues the following messages:

"WARNING:Xst:37 - Unknown property 'INIT_RANGE'."

"ERROR:Parsers:11 - Encountered unrecognized constraint while parsing."

"ERROR:Xst:1338 - XCF parsing failed."

To avoid this problem, set the INIT_xx attribute before the BEGIN statement in the XCF file:

INST u0_RAMB4 INIT_00 ="1a020a0212020140602408060402000806040200080604020001c001c04cb300";

BEGIN model "model_name"




AR# 9455
Date Created 08/21/2007
Last Updated 12/15/2012
Status Active
Type General Article