XST Options, also known as XST properties, Constraints or Attributes,help you toobtain an optimalSynthesis result based on which you willachievebetter design performance. You can use XST Options to control how XST Synthesizes your design, such as HDL sources handling, inferred logic handling, whether or not to use a Synthesis algorithm, and etc.
XST Options are used for Synthesis process.They can be set globally or applied tocertain modules,instances or signals within the RTL or XCF file.
See
(Xilinx Answer 37221) for help applying a constraint globally.
See
(Xilinx Answer 39649) for help applying a constraint within the RTL.
See
(Xilinx Answer 39650) for help applying a constraint with an XCF.