"ERROR:Xst:853 - Unsupported item in port list for module <module_name>"
NOTE: You can use an anonymous port to describe ports that have no internal connection. This is useful when your design is implemented with a pre-determined interface (set of ports), but the design does not need to connect to one or more ports internally.
Example of an anonymous port:
module ff (d, clk, q, );
The empty space after the port "q" is the anonymous port. XST does not currently support anonymous ports.
Port Width Declared in the Port Listing Declaring port widths in the port listing is standard Verilog coding; however, declaring ports widths in the port listing is not currently supported in Verilog sub-modules. To work around this issue, declare the widths of the ports in the port declarations and not in the port lists.