Hi guys,

I'm trying to use the asynchronous input synchronization template from
ISE 10.1, but I get a double warning I do not understand:

WARNING:ConstraintSystem:119 - Constraint <NET: UniqueName:
/SigGenTop/EXPANDED/S0\/sreg<1> HBLKNM = "sync_reg">: This constraint
cannot
be distributed from the design objects matching 'NET: UniqueName:
/SigGenTop/EXPANDED/S0\/sreg<1>' because those design objects do not
contain
or drive any instances of the correct type.

WARNING:ConstraintSystem:119 - Constraint <NET: UniqueName:
/SigGenTop/EXPANDED/S0\/sreg<0> HBLKNM = "sync_reg">: This constraint
cannot
be distributed from the design objects matching 'NET: UniqueName:
/SigGenTop/EXPANDED/S0\/sreg<0>' because those design objects do not
contain
or drive any instances of the correct type.

Anybody can explain what this means, and how I can avoid it?

-------------
Synchronizer:
-------------

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity syncronizer is
Port ( clk : in std_logic;
async_in : in STD_LOGIC;
sync_out : out STD_LOGIC);
end syncronizer;

architecture Behavioral of syncronizer is

signal sreg : std_logic_vector(1 downto 0);

attribute TIG : string;
attribute IOB : string;
attribute ASYNC_REG : string;
attribute SHIFT_EXTRACT : string;
attribute HBLKNM : string;

attribute TIG of async_in : signal is "TRUE";
attribute IOB of async_in : signal is "FALSE";
attribute ASYNC_REG of sreg : signal is "TRUE";
attribute SHIFT_EXTRACT of sreg : signal is "NO";
attribute HBLKNM of sreg : signal is "sync_reg";

begin

process (clk)
begin
if clk'event and clk='1' then
sync_out <= sreg(1);
sreg <= sreg(0) & async_in;
end if;
end process;

end Behavioral;

--------------
Instantiation:
--------------

S0: entity WORK.syncronizer
port map(Clk=> MClk, async_in => SS, sync_out => synchedSS);

//michael

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