using virtual pins to prevent optimization of unconnected ports

Hi,

How does one declare a virtual pin? At the module i/o declaration or at the time of instance? My guess was declaring it at the time of instantiating a module. But that did not work in quartus and it ignored it. I just want to preserve the unconnected module ports and prevent any optimization of logic connected to these unconnected ports. I figured declaring those ports as virtual pins was the easy way to do it.

e.g.

module top (

input wire a,

input wire [7:0] b

);

foo foo_bar (

.a (a),

.b (b),

.c ( ) /* synthesis altera_attribute="-name VIRTUAL_PIN ON" */

);

endmodule //top

Any thoughts?

Thanks.

Best regards,