asimut: Getting a ?u in the output pattern with structural simulation

[Ashwith Rego]

Hi,

I have the following code for an inverter:

============================
--inverter (NOT) gate
entity invg is port
(
  a   : in  bit;
  x   : out bit;
  vdd : in bit;
  vss : in bit
);
end invg;

architecture vbe of invg is begin
  x <= not (a);
end vbe;
============================

I saved this in invg.vbe Next I ran the following commands:
  boom -l 3 -d invg
  boog invg_o invg -x 1 -m 2

This resulted in the file invg.vst which contains the following:

============================
entity invg is
   port (
      a   : in      bit;
      x   : out     bit;
      vdd : in      bit;
      vss : in      bit
 );
end invg;

architecture structural of invg is
Component inv_x2
   port (
      i   : in      bit;
      nq  : out     bit;
      vdd : in      bit;
      vss : in      bit
 );
end component;


begin

x_ins : inv_x2
   port map (
      i   => a,
      nq  => x,
      vdd => vdd,
      vss => vss
   );


end structural;
============================

I now created a pattern to drive the input. However I see a ?u in the
output. I ran the following command
  asimut invg invg invg_out

I do not see this problem when I run behavioral simulations. The
output patterns file is as below. The input file contains ?* instead
of the ?u

============================
-- description generated by Pat driver

--			date     : Sun May 20 14:50:49 2012
--			revision : v109

--			sequence : invg

-- input / output list :
in       vdd B;
in       vss B;
in       a B;
out      x B;

begin

-- Pattern description :

--                                 vva x
--                                 ds
--                                 ds

                                 : 100?u;
                                 : 101?u;

end;
============================

Is there something I'm doing wrong that is causing the output to show
as undefined?

The code is from this e-book which I am using to learn about the
alliance package:
http://www.cc.toin.ac.jp/sc/palacios/openbook/vlsie.pdf (1.8MB)

Thanks,
Ashwith J. Rego
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