QuestaSim Compiler & Simulator

Run Verilog and SystemVerilog projects with QuestaSim or ModelSim directly from VS Code. Generate a source list, compile your design, run a testbench, and read the complete simulator transcript without switching to an external terminal.

What you need

Before using this extension, make sure that:

• QuestaSim or ModelSim is installed on your computer.
• You have opened your HDL project folder in VS Code.
• Your project contains Verilog/SystemVerilog files (.v, .sv, .vh, or .svh).
• You know the name of the simulation testbench top module, such as alu_tb or up_down_counter_tb.

Select the testbench as the top module in the normal workflow. The testbench instantiates and drives your RTL design, then checks the result. Select an RTL module only when you intentionally want to simulate it by itself.

First-time setup

1. Install the extension

Install QuestaSim Compiler & Simulator from the VS Code Marketplace, then reload VS Code if it asks you to.

2. Open your Verilog project

Use File → Open Folder... and open the folder containing your RTL and testbench files.

For example:

counter-project/
├── rtl/
│   └── up_down_counter.v
└── tb/
    └── up_down_counter_tb.v

3. Choose the testbench top module

Open the Command Palette and run Questa: Select Top Module.

You can select a testbench file or type its module name manually. For the example above, enter:

up_down_counter_tb

The extension saves this as the workspace setting questa.topModule.

Run your first simulation

Follow these steps in order:

1. Run Questa: Generate Source List.

   • Creates sources.f in the project root.
   • Finds HDL source files automatically.

2. Run Questa: Generate run.do.

   • Creates sim/run.do by default.
   • Creates the simulation directory when it does not exist.

3. Run Questa: Compile.

   • Refreshes sources.f.
   • Creates or maps the Questa work library in sim/.
   • Runs vlog and shows the complete output in VS Code.

4. Run Questa: Run Simulation.

   • Runs your configured testbench.
   • In console mode, runs vsim -c and exits after the testbench finishes.

5. Open the transcript if it is not already visible.

   • Run Questa: Show Transcript, or select QuestaSim in View → Output.

The expected generated files look like this:

counter-project/
├── rtl/
├── tb/
├── sources.f
└── sim/
    ├── run.do
    └── work/

Everyday workflow

After setup, the usual loop is simple:

Edit RTL or testbench
        ↓
Questa: Compile
        ↓
Questa: Run Simulation
        ↓
Read results in the QuestaSim Output channel

With questa.autoGenerateSourceList enabled (the default), sources.f is refreshed automatically when HDL files are added, edited, renamed, or removed.

Click $(play) Questa in the VS Code status bar to open quick access to Compile, Run Simulation, source generation, the transcript, and settings.

Simulation modes

The default is console simulation:

{
  "questa.simulationMode": "console"
}

Use GUI mode to open the QuestaSim graphical window:

{
  "questa.simulationMode": "gui"
}

You can also run Questa: Open Waveform, which launches the generated script in GUI mode. Waveforms are displayed by QuestaSim itself.

Configuration reference

Add these settings to your workspace when needed:

{
  "questa.vsimPath": "C:/questasim/bin/vsim.exe",
  "questa.vlogPath": "",
  "questa.topModule": "alu_tb",
  "questa.simulationDirectory": "sim",
  "questa.sourceListFile": "sources.f",
  "questa.runDoFile": "run.do",
  "questa.simulationMode": "console",
  "questa.autoGenerateSourceList": true,
  "questa.includeDirectories": ["rtl/include"],
  "questa.macroDefinitions": ["SIMULATION", "WIDTH=8"],
  "questa.additionalVlogArguments": [],
  "questa.additionalVsimArguments": []
}

simulationDirectory is relative to your workspace by default. It keeps generated scripts and Questa work libraries separate from your RTL source tree.

Source-file order

The extension uses this sensible default order:

1. Header and include files (.vh, .svh)
2. Package files (for example, *_pkg.sv)
3. RTL source files
4. Testbench files (for example, files in tb/ or ending with _tb.sv)

For projects that require a strict custom order, set questa.sourceOrder with ordered glob patterns:

{
  "questa.sourceOrder": [
    "rtl/packages/**/*.sv",
    "rtl/**/*.sv",
    "rtl/**/*.v",
    "tb/**/*.sv"
  ]
}

The scanner excludes generated and dependency folders such as .git, node_modules, .vscode, work, build, and sim. Add or change excluded folder names with questa.excludedDirectories.

Existing run.do scripts

Many projects already have a hand-written simulation script. Use Questa: Run Existing run.do to find and run one without changing it.

When you use Questa: Generate run.do, the extension never silently overwrites an existing user-created run.do. It offers to create run_generated.do, overwrite only after confirmation, or cancel.

Commands

Troubleshooting

“QuestaSim executable was not found”

Set questa.vsimPath to the full path of vsim.exe on Windows, or vsim on Linux. Confirm the path points to the QuestaSim installation, not a shortcut.

“No top module configured”

Run Questa: Select Top Module and choose or enter the testbench module name.

Compilation errors or simulation failures

Run Questa: Show Transcript. The Output channel contains the complete vlib, vmap, vlog, and vsim messages, including the original file and line reported by QuestaSim.

My files compile in the wrong order

Configure questa.sourceOrder as shown above. This is common when packages, interfaces, or generated source files have dependencies that cannot be inferred from filenames.

Optional: Configure the QuestaSim installation path

You normally do not need this step. If Questa: Compile already works, VS Code has found QuestaSim through your system PATH.

Only configure these paths if the extension reports that vsim, vlog, vlib, or vmap cannot be found, or if you want this workspace to use a specific QuestaSim installation.

Open the Command Palette (Ctrl+Shift+P), run Preferences: Open Workspace Settings (JSON), and add:

{
  "questa.vsimPath": "C:/questasim/bin/vsim.exe",
  "questa.vlogPath": "C:/questasim/bin/vlog.exe"
}

If vlog.exe is in the same folder as vsim.exe, questa.vlogPath is optional; the extension derives it automatically.

Linux example:

{
  "questa.vsimPath": "/opt/questasim/bin/vsim",
  "questa.vlogPath": "/opt/questasim/bin/vlog"
}

Author & links

• LinkedIn — Ahmed Nossier
• YouTube — Nossier1