How to convert an existing project to Hog#

Converting an existing project to Hog means: copying the source files into a git repository, adding Hog as a submodule, creating the Hog list files (text files containing the names of your source files), and writing a hog.conf file, storing the project’s properties.

Before starting#

We assume that you are starting from a clean repository and you want to convert a Vivado project stored in a local folder.

If you are migrating to Hog but you are not changing repository, you can follow the instructions below ignoring the creation of the new local repository. In this case you might want to work in a new branch of your repository.

Let’s suppose your new repository is called new_repo with URL new_repo_url, your project is named myproject and it is currently stored in some local folder mypath. If you do not have a new repository, you can go on GitLab and create one.

Creating the git repository#

First of all create a new folder where you will store your firmware, initialise it as a git repository and connect it to the remote repository:

  mkdir new_repo
  cd new_repo
  git init
  git remote add origin <new_repo_url>

Here <new_repo_url> is the url to your new empty repository: you can obtain the url by connecting to your gitlab server, creating a new repository and then copying the url from the clone button in the project page.

For the moment, we are going to work on the master branch, that is the default one. If you want, you can create a branch and work on that:

git checkout -b first_branch
git push origin first_branch

Add Hog to your project#

Hog repository should be included as a submodule in the root path of your repository. To do this, type:

git submodule add ssh://

Here we assumed that you want to use the ssh protocol. If you want to use https enter

git submodule add

If you prefer krb5:

git submodule add

However, it is a good idea to not include the submodule protocol explicitly, but to let it be inherited from the repository Hog is included into. To obtain this edit a file called .gitmodules with your favourite text editor (say vim):

vim .gitmodules

In that file, you should find a section as in the following. Modify the URL value by replacing it with a relative path. Note that the URL that must be specified relative to the path of your repository:

  [submodule "Hog"]
    path = Hog
    url = ../../hog-cern/Hog.git

If your repository is stored on the URL specified in your .gitmodules should be

  url = ../../hog/hog.git

Now from your repository:

git submodule update

This should trigger an error if you made a mistake when editing the repository path.

Copying some templates from Hog and committing#

Now that you have Hog locally, you can start setting up your repository. Hog provides a set of templates that you can use. For example, you can add a .gitignore to your repository with the following command:

cp Hog/Templates/gitignore .gitignore


You might need to modify your .gitignore file, if you have a more complicated directory structure, especially for the IP and BD files. For example, the Hog template assumes that you store your IPs in IP/ip_name/ip_name.xci. In this case, this file would be enough for you. If your IPs are stored in different directories, you can use several .gitignore files.

Let’s now make our first commit:

git add .gitignore .gitmodules Hog
git commit -m "Adding Hog to the repository"
git push origin master

If you are working in a branch that is not master, please replace the last instruction with:

git push origin your_branch_name

Early tagging your repository#

Hog assumes that at least a version tag of the form vM.m.p is present in your repository. Let’s now create the first Hog tag:

  git tag -m "First version" v0.0.1
  git push --tags

The tag message is necessary as it prevents git from creating a lightweight tag.

Convert your project to Hog#

Automatic conversion#


This feature is currently only supported for Vivado.

If you want to integrate your project(s) within the Hog framework and you do not want to modify your directory structure, you can do it almost automatically. You have to copy your entire directory content, including the Vivado project, into the new repository:

cp ../old_repo/* .


If your project contains submodules, they shall not be copied from the original repository, but rather added as submodules. Please check the submodules section for extra details.

Now, you have to run the script, by issuing:


This script will, among other things, scan for all the (not Hog) Vivado projects within your current directory and (optionally) convert them into Hog projects. It automatically creates a directory called Top, containing one subdirectory for every Vivado project that was converted. If you browse those subdirectories, you will find that they contain a file called Top/myproject/hog.conf and another subdirectory called Top/myproject/list. The meaning of each is explained in sections Configuration File and List Files.

Your old Vivado project(s) has now outlived its purpose, and you shall delete it.

At this point, you have to commit your project files (e.g. Top directory, source files, IPs1, etc.) into the repository:

git add Top
git add path_1/file_1.vhd
git add path_2/file_2.xdc
git add path_3/file_3.xci
git commit -m "Adding files to project"

Remember that you can always keep track of the uncommitted files by running:

git status


When you copied the entire content of your old directory, you probably copied also many temporary files that you don’t want to be stored into your repository. When you add the files to the repository, please be particularly careful and select only the ones that are really needed. Setting proper .gitignore rules can help you in this phase.

At this point you should be ready to create your Hog project (stored in the directory Projects), by running:

./Hog/Do CREATE myproject

Manual conversion#

Generating Hog directory structure#

You have to generate a directory structure similar to this one:

A complete description of the meaning of each folder can be found in the Hog User Manual

Top folder#

Every Hog-handled HDL repository must have a directory called Top, which stores the configuration files, necessary to create the HDL projects. Each subdirectory inside Top that contains these configuration files - named project top-directory - represents an HDL project in the repository.

You can start by creating your project top-directory:

mkdir -p Top/myproject

Every project top-directory must contain a subdirectory called list, where the so-called hog list files are stored. Let’s create it:

mkdir Top/myproject/list

A file named hog.conf must be in the project top-directory. Hog reads this configuration file to create a project. This is a recap of what we have learned up to now:

  • A Top folder must be in the repository

  • Inside this folder, there is one subfolder for each project in the repository, called the project top-directory

  • Inside each project’s top-directory there is 1. a list subdirectory containing the list files 2. a hog.conf file;

For more advanced Hog features, additional files and folder are located in the Top folder, but we do not discuss them now for simplicity.

To create the project’s hog.conf script, we will start from the template provided in the Hog/Templates folder:

cp Hog/Templates/hog_vivado.conf Top/myproject/hog.conf

Different templates are provided for Vivado, PlanAhead and Quartus and are named hog_vivado.conf, hog_ise.conf and hog_quartus.conf

Use your favourite text editor to modify the template configuration file. There are several things you can edit, depending on your needs, for example, the FPGA name or the synthesis or implementation strategies. The template contains comments to guide you through the process.

Now you can commit everything you just did:

git add Top
git commit -m "Adding Hog Top folder"


From version 2021.2, Hog support a complex subfolder structure. For instance, one could create the project top-directory inside a subfolder of Top.

mkdir -p Top/subfolder/myproject

In this case, the resulting project name will be subfolder/myproject

Importing source files to the project#

You are now ready to import the files needed to build your project.


Hog gives you the possibility to organise the source files in different VHDL libraries (Verilog does not have the concept of library). You can add your source files into several .src files in the list directory. Each of these will correspond to a different library with the same name as the .src file (excluding the .src extension). For simplicity, in this chapter, we will assume the presence of a unique library with the same name as your project.

First of all, copy the files from your local folder into the git repository. Exception made for some reserved directory (e.g. Top, Projects, bin) you can put your files wherever you like inside your repository.

In this example, we will create a directory named lib_myproject where we will store all the source, simulation and constraint files.

mkdir -p lib_myproject/source lib_myproject/simulation lib_myproject/constraint
cp ../old_repo/source_1.vhd lib_myproject/source
cp ../old_repo/source_2.v lib_myproject/source
cp ../old_repo/simulation_1.vhd lib_myproject/simulation
cp ../old_repo/simulation_2.v lib_myproject/simulation
cp ../old_repo/constraint_1.xdc lib_myproject/constraint
cp ../old_repo/constraint_2.tcl lib_myproject/constraint

After having added all the relevant files in your folders, you have to add their path and file names to the appropriate list files. In this example, we will create:

  • One source list-file called Top/myproject/list/myproject.src, containing the source files of your project

  • One simulation list-file called Top/myproject/list/myproject.sim, containing the files used in the simulation (e.g. test benches, modules that read/write files, etc.)

  • One constraint list-file called Top/myproject/list/myproject.con, containing your constraints (.xdc, .tcl, etc.)


The paths of the files inside the list-files are relative to the main folder of the repository.

If you want, you can add comment lines in the list-files starting with a # and you can leave empty lines (or lines containing an arbitrary number of spaces). All of these will be ignored by Hog.

At this point, you might want to check that the files are correctly picked up by regenerating the Hog project. Hog will give you an error if a file is not found.

./Hog/Do CREATE myproject

You can open the created project in Projects/myproject/myproject.xpr (or Projects/myproject/myproject.qpf for Quartus) with the GUI and check that all the files are there. If not, modify the list files and create the project again. When you are satisfied, you can commit your work:

git add lib_myproject
git add Top/myproject/list/myproject.src
git add Top/myproject/list/myproject.sim
git add Top/myproject/list/myproject.con
git commit -m "Adding source files"


If your project uses source or simulation files hosted in a separate repository you can add that repository as a git submodule.

git submodule add my_submodule_url

You can add your submodules wherever you like in your repository.

In the same fashion as the source files contained in your repository, files taken from a submodule must be added to a Hog list file.

Intellectual Properties (IP)#

IP files can be stored anywhere in your repository or submodules. However, particular care must be taken to avoid that the files generated by Vivado or Quartus are kept separated and not committed to the repository. To achieve this, these simple rules must be followed:

  • each IP file (.xci for Vivado) must be contained in a sub-folder called with the same name as the .xci file (extension excluded).

  • only the IP file must be committed to the repository (e.g. .xci for Vivado, .ip for Quartus)

  • a .gitignore file must be used to tell git to ignore all non-IP files, a template is provided in the Templates directory.

Basically for each IP in your project, run:

  mkdir -p path_to_your_ips/ip_name/
  cp ../old_repo/ip_name.xci path_to_your_ips/ip_name/

Then you must add the .xci files to the .src list file you want. In this case, we will use a separate file called IP.src.


There is no concept of library for the IPs, so we prefer to put them in a separate .src file. You can put them in the same list file as your other source files if you wish. Just open Top/myproject/list/myproject.src with a text editor and add them there.

As usual, you can check that the files are correctly picked up by regenerating the project.

./Hog/Do CREATE myproject

If you are satisfied with the changes, you can commit your work.

  git add path_to_your_ips
  git add Top/myproject/list/IP.src
  git commit -m "Adding IP Files"

If you have .coe files for RAM initialisation or analogous files please make sure that you add them to a .src list file and that you specify them with a relative path when customising the IP.

The top module of your project#

You can specify the top module with the property top=top_module_name. For example, if your top module is called mytop and it is stored inside a mytop.vhd file, your list file would look like,

# This is an example .src file
mytop.vhd top=mytop


If you don’t specify it, Hog will use the default value top_<project_name>, as top module for your project.

Hog provides a set of parameters/generics to your top module at the beginning of the synthesis. You should add the Hog parameters/generics to your top module to store those values in some registers. The complete list of the variables can be found here. The templates provided in ./Hog/Templates/, contain all the generic/parameter names.

We have to customise the library names. In our case, there is only one library called myproject.

Code documentation#

Hog can be help you to document VHDL code, automatically generating and deploying the documentation. Hog works with Doxygen version 1.8.13 or later. If your code already uses Doxygen style comments, you can easily generate Doxygen documentation. You just have to create a directory named doxygen containing the files used to generate the VHDL documentation. A file named doxygen.conf should be in this directory together with all the files needed to generate your Doxygen documentation. You can copy a template configuration from Hog/Templates/doxygen.conf and modify it.


IP files require special care. Please check the section IPs