Need help to allow unused logic in ISE 9.1i

Hello,

I'm trying to allow some block in a Xilinx Fpga in order to evaluate the necessary size.
I need to know if is possible to set the Xilinx syntetizer to avoid to clear implementation not used yet, for example if I have:

entity prj1 is
port (clk : in std_logic;
d : in std_logic;
q : out std_logic;
datain : in std_logic_vector(3 downto 0)

);
end prj1;


architecture BEH of prj1 is
signal test: std_logic;


begin

strobe_gen: process(clk)
begin
if (clk'event and clk = '1') then
q <= d;
end if;
end process;

test <= datain(3) and datain(2) and datain(1) and datain(0);

end BEH;


The sygnal test for now is unused, I woud like to have in my project the FF and the 4 input AND; if I syntetize with ISE I obtain only a FF.
Thanks for all

D

Hi

Declare the VHDL constraint in signal declaration section as follows

attribute s : yes;

attribute s of tmp : signal is "Yes";

To know more about this one, refer SAVE NET FLAG section of the Xilinx Constraints Guide manual.