Disabled generate give compile error in Modelsim...




It has been a while since I used VHDL so I am a little rusty. Did not
much use the generate statement in the past either. And now I have the
problem that I have (been given) a VHDL model that has a conditional
generate in it. And this does not work as I expected. In the model, the
purpose of the conditional is that there is a clock source that cannot be
simulated, so an alternative is simulated. I have reproduced the problem
in the minimal example below.

If I decalare \'sigio\' as \'inout\', as below and as I got the model, then when
I simulate it, the signals in the simulation remain \'U\'. So somehow the
\'gentest\' model drives the \'sigio\' signal although the generic
\'this_is_a_simulation\' has been set to true.

If I declare \'sigio\' as \'in\' (change the comment line in the port), I get a
compilation error in Modelsim on driving the type \'in\' \'sigio\' signal. When
I then just comment out the \'rtlblk\' generate, the model simulates as

Can this be made to work as expected (simulation/pll model switch without
changing the code)? Unfortunately I cannot get information from the original
creator of this construct and I don\'t know if it ever worked.

-------- gentest.vhd ------------
library ieee;
use ieee.std_logic_1164.all;

entity gentest is
this_is_a_simulation : boolean := true
-- sigio : in std_logic;
sigio : inout std_logic;
sigout : out std_logic
end entity gentest;

architecture behav of gentest is

rtlblk : if this_is_a_simulation = false generate
sigio <= \'1\';
sigout <= \'1\';
end generate;

simblk : if this_is_a_simulation = true generate
sigout <= sigio;
end generate;

end architecture behav;

-------- tb_gentest.vhd ------------
library ieee;
use ieee.std_logic_1164.all;

entity tb_gentest is
end entity tb_gentest;

architecture behav of tb_gentest is
signal clk : std_logic;
signal sigout : std_logic;

gentest_inst : entity work.gentest
generic map(
this_is_a_simulation => true
port map(
sigio => clk,
sigout => sigout

clk <= \'0\';
wait for 10ns;
clk <= \'1\';
wait for 10ns;
end process;

end architecture behav;


Hey, where did that sig go?!

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