Hog supports all simulation software currently supported by Vivado (click here for the full list). Hog simulation has been tested with Vivado Simulator (also called Xsim), Mentor Graphics Questasim, Mentor Graphics Modelsim and Aldec Riviera Pro.

The simulation setup is always handled by Vivado, as if the simulation button on the GUI was clicked, then the simulation run is done with the simulation software.


Currently the simulation is not supported under Quartus. A complete support will be included in the next releases.

Simulation sets#

Simulations are organised in so-called “simulation sets” as in Vivado.

simulation sets

In this figure, you can see an example of simulation sets, these are contained in Vivado in the Simulation_Sources folder in the hierarchy view. You can right click on each of them, set it as active (becomes bold) and run it by clicking the “Run simulation button”. In the figure above algo_sim is the active simulation.

Every simulation set has a top entity, the test bench containing the device under test, and can be simulated independently.

Hog creates a simulation set for each .sim list file in the Top project folder (Top/myproj/list). It is also possible to have multiple simulation libraries in the same simulation file sets. To do so, you should assign the lib=library_name property to the included file or sim list file in the .sim list file in the Top simulation folder.

For example, if you have a simulation list file called mysim in your Top project folder with the following content,

src/lib1/lib1_sim.vhd lib=lib1
src/lib2/lib2.sim lib=lib2

this will create a simulation file set mysim in Vivado with three libraries: mysim, lib1 and lib2.


Vivado creates by default a simulation fileset called sim_1. To use it in Hog, simply creates a list file called sim_1.sim in your list folder.

Simulation Configuration File#

The simulation properties are read from another file called ./Top/<my_project>/sim.conf, with a similar syntax as the hog.conf. The need for a separate file lies on the fact that touching the simulation properties does not affect the actual firmware which will be synthesised. Thus we don’t want Hog to change the version of the project, when the developers touch only the simulation.

Simulation properties can be set individually for each simulation set, or globally for all of them. For example, to set xsim.elaborate.rangecheck property for the simulation set sim_1, you should write

xsim.elaborate.rangecheck = true

Alternatively, if you want to set this property for all your simulation sets, you should write.

xsim.elaborate.rangecheck = true

A typical sim.conf file would look like then:



Please note that the for the settings that require the name of a file, for instance CUSTOM_UDO or CUSTOM_WAVE_DO, only the file name must be set, and not the full path. Remember also to include these files in your .sim list file, in order to add them to the Vivado project.

Hog also offers the possibility to generate the sim.conf automatically, by clicking on the Hog Conf Button in the Vivado GUI.

Remember that individual simset properties have always the priority with respect to the global. So you can set a global property for all your simsets, and change it just for one of them, for example.

To set a particular simset as the active one, you need to set the ACTIVE property to 1 in your sim.conf, under the relative simset section. If no active simset is specified, Hog will set as active the last created simulation set.


In Hog versions older than Hog2022.2, only a limited set of simulation properties could be specified. These properties were directly set inside the .sim files and were:

  • topsim=<entity_name>: (mandatory) the name of the entity that will be the top level of the simulation;

  • runtime=<time>: (optional) it indicates the running time for your simulation;

  • wavefile: (optional) it indicates the name of the entity you want to set as top level in your simulation;

  • dofile: (optional) it indicates the file containing the signal waveforms to be observed in your simulation.

In Hog2022.2, properties defined in the sim.conf files have always the priorities, but the tool will still set those that are defined in the .sim list files. Altough, please note, that we plan to deprecate this feature in future releases, where only the sim.conf file will be supported.

Generics section#

Similarly to the hog.conf, from Hog2023.1 it is possible to pass generics value to the top simulation file in your Vivado project, by defining them in the specific [generics] section in the sim.conf file. For example,


Currently, generics are passed to the top modules of all your simulation file sets, but we foreseen in the future the possibility to pass different generics to the individual simulation sets.

Project simulator#

The software used to simulate is set at project level in Vivado. To change it you have to change the “target_simulator” property in the “main” section of your hog.conf file.


Vivado does not allow to run different simulations with different simulators automatically. If you want to do that locally, you have to go every time to the simulation settings to switch from one simulator to another. The setting will be valid at project level, so for all the simulations sets. If you change the simulator by clicking in Vivado GUI, the change will not be propagated to the repository.

Simulation Library#

When using an external simulation software, it is necessary to specify the path to the compiled simulation library. By default, Hog sets this path to repo_path/SimulationLib, where repo_path is the root folder of your git repository. In the case that the HOG_SIMULATION_LIB_PATH environmental variable is defined, as in the Continuous Integration (see here and here), Hog will set the path to it.

Finally, it is also possible to specify the simulation library path, when creating the project, using the --lib flag

    ./Hog/Do CREATE <myproj> -lib <library_path>

Simulation in the CI#

If the simulation job is configured in your projects CI, the Hog CI will automatically run the simulation sets.

The CI stage will fail if one simulation fails. This means that, in order for the CI stage to be meaningful, each simulation set should be designed to fail if some unwanted behaviour is present.

Even if Vivado does not allow for different simulators in the same project, in Hog CI it is possible to specify a different software to be used in each set. This can be done by adding at the top of the .sim list one of the following lines:

    #Simulator xsim       # For Vivado Simulator
    #Simulator questa     # For QuestaSim Simulator
    #Simulator modelsim   # For ModelSim Simulator
    #Simulator riviera    # For Aldec Riviera Simulator
    #Simulator activehdl  # For Aldec Active-HDL Simulator
    #Simulator ies        # For IES Simulator 
    #Simulator vcs        # For Synopsys VCS Simulator

    #Simulator skip_simulation #To skip the simulation in the CI

If you do not specify the simulator software, Hog will set ModelSim as default.

If for any reason, you do not want a specific simulation set to be simulated by the CI, just use skip_simulation.

An example .sim list file looks like this

    #Simulator Xsim

Simulating without GUI#

If you want to run the simulation locally, but without using the GUI (i.e. in the same way that CI does), you can use the Hog/Do script.

    ./Hog/Do SIMULATE <project name> [-lib_path <sim lib path>] [-simset <sim sets>] [-quiet] [-recreate]

This script will launch all the simulation sets in the specified projects, using the software specified in the .sim file and skipping the simulation if skip_simulation is specified. More details can be found here.