====== GHDL ======
GNU Hardware Description Language, an open-source version of VHDL.

===== Installation Ubuntu 18.04 =====
<code bash>
sudo apt update
sudo apt install -y git make gnat zlib1g-dev
git clone https://github.com/ghdl/ghdl
cd ghdl
./configure --prefix=/usr/local
make
sudo make install
echo "$0: All done!"
</code>

===== Hello world =====
<code vhdl>
--  Hello world program
use std.textio.all; -- Imports the standard textio package.

--  Defines a design entity, without any ports.
entity hello_world is
end hello_world;

architecture behaviour of hello_world is
begin
  process
    variable l : line;
  begin
    write (l, String'("Hello world!"));
    writeline (output, l);
    wait;
  end process;
end behaviour;
</code>