AR# 21775: 13.1 EDK - How can I pass XST switches?
13.1 EDK - How can I pass XST switches?
Is there a way to pass XST switches and constraints in EDK?
You can pass XST options by creating XCF files for your instantiated cores. Then, put the XCF files into the <proj>/etc/ directory. For example, most instantiated cores have a wrapper HDL file as it's the top level file. This would then need an XCF file as <instance>.xcf (no wrapper in the XCF name) in the <proj>/etc/ directory.
For more information on XST Constraint Files (XCF), refer to the XST User Guide.
This flow is unsupported in that it has not been tested and is not guaranteed to exist in future releases. Otherwise, there should not be any problems using this flow.