Using ghdl instead of Quartus II

ghdl is a great tool to prototype hardware quickly. It can be combined with gtkwave to analyze signals.

I did hardware design last semester and this is a bit tough for my mind right now, but I think it could help others out having a hard time with Quartus II. This post explain how to replace Quartus in the process of developing the device …

First of all, you need ghdl and gtkwave installed on your workstation.

yum install ghdl gtkwave

Then you can create a sample project or clone one I did last semester.

git clone https://github.com/arteymix/ghdl-lmc.git

A project usually consist of entities and testbeds on these entities. A testbed applies entries on an entity and make assertions on outputs.


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42

library ieee;

use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;

entity testbed is
end entity;

architecture testbed of testbed is

    type inputs_t is array(0 to 255) of signed(11 downto 0);

    constant inputs: inputs_t := (
        0 => x"000",
        1 => x"123",
        2 => x"456",
        3 => x"ABC",
        others => x"000"
    );

    signal cycle: natural             := 0;
    signal clk:   std_logic           := '1';
    signal input: signed(11 downto 0) := inputs(cycle);

begin
    input <= inputs(cycle mod 256);
    lmc: entity work.lmc port map(clk, '1', input);
    process is
    begin

        while TRUE loop
            clk <= '1';
            wait for 10 ns;
            clk <= '0';
            wait for 10 ns;
            cycle <= cycle + 1;
        end loop;

    end process;
end architecture;

ghdl can generate a Makefile for a specified unit

ghdl --gen-makefile testbed

ghdl can analyze, elaborate or run a simulation. The analyze part is essential as it will generate object files for each entities. Then you can link all those into a single executable. This is automated by the make command.

make

Once you have a correct result, you may run it and capture signals

./testbed --vcd=testbed.vcd

gtkwave is a tool designed to analyze signals, specifically the generated vcd file.

gtkwave testbed.vcd

In gtkwave, you have to select the device in SST section and append the signals on your workarea. You may then zoom it and out to see the actual waves.

I really hope this will help you out! I did enjoy VHDL and I really liked learning Ada-like syntax.