Please refer to this answer record for help debugging coding issues with XST.
Note: This Answer Record is a part of the Xilinx Solution Center for XST (Xilinx Answer 38927).
The Xilinx Solution Center for XST is available to address all questions related to XST.
Whether you are starting a new design or troubleshooting a problem, use the Solution Center for XST to guide you to the right information.
Synthesizable RTL can be broken down into the following categories:
See (Xilinx Answer 39079) for help debugging issues regarding inference.
Many Xilinx primitives and/or macros can be inferred; although not all. When running into any inference concerns, please refer to this section of the design assistant.
See (Xilinx Answer 39648) for help debugging issues with instantiations.
Whether instantiating a lower level module, black-box, or a primitive this is a great starting point to help debug instantiation issues.
See (Xilinx Answer 40085) for help with performance considerations.
XST provides performance enhancements to help achieve high speed design.