Problems with GHDL and GTKWave

[Christian Christmann]

Hi,

I'm new to VHDL. After looking for a free VHDL simulator
I found GHDL.

I started reading the manual and wanted to implement a
full adder as described here:
http://ghdl.free.fr/ghdl/A-full-adder.html#A-full-adder

So, first of all I've implemented the full adder with a
behavioral description:
------
entity adder is
port( i0, i1 : in bit;
ci : in bit;
s : out bit;
co : out bit );
end adder;

architecture rtl of adder is
begin
s <= i0 xor i1 xor ci;
co <= (i0 and i1) or (i0 and ci) or (i1 and ci);
end rtl;
-------

and analyzed it with "ghdl -a adder.vhdl".

Then I wrote the testbench adder_tb.vhdl:

----------
entity adder_tb is
end adder_tb;

architecture behav of adder_tb is
component adder
port ( i0, i1 : in bit;
ci : in bit;
s : out bit;
co : out bit );
end component;

for adder_0: adder use entity work.adder;
signal i0, i1, ci, s, co : bit;
begin
adder_0: adder port map( i0 => i0, i1 => i1, ci => ci,
s => s, co => co );

process
type pattern_type is record
i0, i1, ci : bit;
s, co : bit;
end record;

type pattern_array is array (natural range <&gt of pattern_type;
constant patterns : pattern_array :=
(('0', '0', '0', '0', '0'),
('0', '0', '1', '1', '0'),
('0', '1', '0', '1', '0'),
('0', '1', '1', '0', '1'),
('1', '0', '0', '1', '0'),
('1', '0', '1', '0', '1'),
('1', '1', '0', '0', '1'),
('1', '1', '1', '1', '1'));

begin
for i in patterns'range loop
i0 <= patterns(i).i0;
i1 <= patterns(i).i1;
ci <= patterns(i).ci;

wait for 1 ns;

assert s = patterns(i).s
report "bad sum value" severity error;
assert co = patterns(i).co
report "bad carray out value" severity error;

end loop;
assert false report "end of test" severity note;
wait;
end process;
end behav;
-----------

After analyzing with "ghdl -a adder_tb.vhdl", building
with "ghdl -e adder_tb" and finally running the testbench
with "ghdl -r adder_tb --vcd=adder.vcd", I get the VCD
waveform adder.vcd.

Then I wanted to view the waveform output with gtkwave,
but after "gtkwave adder.vcd" I don't see the waves but an
empty window. Any ideas what's wrong?
Or do I have to set up gtkwave?

Thank you.

Chris

 

Christian Christmann wrote:

Then I wanted to view the waveform output with gtkwave,
but after "gtkwave adder.vcd" I don't see the waves but an
empty window. Any ideas what's wrong?
Or do I have to set up gtkwave?

You have to import the traces from the tree or hierarchy requesters.
As a trace could have thousands of nets, they're not imported
automatically.

Turn to page 44 (Displaying Waveforms) in the User's Guide which can be
found on a link at the bottom of http://home.nc.rr.com/gtkwave/

-t