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Verify Generated Code Using HDL Test Bench from Configuration Parameters

This example shows how to generate a HDL test bench and verify the generated code for your design. The example assumes that you have generated HDL code for your model. If you haven't generated HDL code, you can still open this model and generate the HDL test bench. Before generating the test bench, HDL Coder™ runs code generation to make sure that there is at least one successful code generation run before generating the testbench.

This example illustrates how to verify the generated code for the FIR filter model. To learn how to generate HDL code for this model, see Generate HDL Code from Simulink Model Using Configuration Parameters.

FIR Filter Model

This example uses the Symmetric FIR filter model that is compatible for HDL code generation. To open this model at the command line, enter:


The model uses a division of labor that is suitable for HDL design.

  • The symmetric_fir subsystem, which implements the filter algorithm, is the device under test (DUT). An HDL entity is generated from this subsystem.

  • The top-level model components that drive the subsystem work as a test bench.

The top-level model generates 16-bit fixed-point input signals for the symmetric_fir subsystem. The Signal From Workspace block generates a test input (stimulus) signal for the filter. The four Constant blocks provide filter coefficients. The Scope blocks are used for simulation and are not used for HDL code generation.

To navigate to the symmetric_fir subsystem, enter:


Symmetric FIR filter algorithm.

Create a Folder and Copy Relevant Files


  1. Create a folder named sl_hdlcoder_work, for example:

    mkdir C:\work\sl_hdlcoder_work

    sl_hdlcoder_work stores a local copy of the example model and folders and generated HDL code. Use a folder location that is not within the MATLAB folder tree.

  2. Make the sl_hdlcoder_work folder your working folder, for example:

    cd C:\work\sl_hdlcoder_work
  3. Save a local copy of the sfir_fixed model to your current working folder. Leave the model open.

What is a HDL Test Bench?

To verify the functionality of the HDL code that you generated for the DUT, generate a HDL test bench. A test bench includes:

  • Stimulus data generated by signal sources connected to the entity under test.

  • Output data generated by the entity under test. During a test bench run, this data is compared to the outputs of the VHDL® code, for verification purposes.

  • Clock, reset, and clock enable inputs to drive the entity under test.

  • A component instantiation of the entity under test.

  • Code to drive the entity under test and compare its outputs to the expected data.

You can simulate the generated test bench and script files with the Mentor Graphics® ModelSim® simulator.

How to Verify the Generated Code

This example illustrates how to generate a HDL test bench to simulate and verify the generated HDL code for your design. You can also verify the generated HDL code from your model using these methods:

Verification MethodFor More Information
Validation ModelGenerated Model and Validation Model
HDL Cosimulation (requires HDL Verifier™)Cosimulation
SystemVerilog DPI Test Bench (requires HDL Verifier)SystemVerilog DPI Test Bench
FPGA-in-the-Loop (requires HDL Verifier)FPGA-in-the-Loop

Generate HDL Test Bench

Depending on whether you generated VHDL, Verilog or SystemVerilog code, generate VHDL, Verilog or SystemVerilog test bench code. The test bench code drives the HDL code that you generated for the DUT. By default, the HDL code and the test bench code are written to the same target folder hdlsrc relative to the current folder.

For the FIR filter, the symmetric_fir subsystem is the DUT. To generate the testbench, select this subsystem. You cannot generate a HDL testbench for an entire model.

  1. In the Apps tab, select HDL Coder. The HDL Code tab appears.

  2. Select the DUT Subsystem in your model, and make sure that this Subsystem name appears in the Code for option. To remember the selection, you can pin this option. Click Generate Testbench.

By default, HDL Coder generates VHDL testbench code in the target hdlsrc folder.

Generate Verilog or SystemVerilog Test Bench Code

If you want to generate Verilog or SystemVerilog test bench code, you can specify this setting in the HDL Code Generation pane of the Configuration Parameters dialog box.

To generate Verilog testbench code for the counter model:

  1. In the HDL Code tab, click Settings.

  2. In the HDL Code Generation pane, for Language, select Verilog or SystemVerilog. Leave other settings to the default.

  3. In the HDL Code Generation > Test Benchpane, click Generate Test Bench.

If you haven't already generated code for your model, HDL Coder compiles the model and generates HDL code before generating the test bench. Depending on model display options such as port data types, the model can change in appearance after code generation.

As test bench generation proceeds, HDL Coder displays progress messages. The process should complete with the message

### HDL TestBench Generation Complete.

After generating the test bench, you see the generated files in the hdlsrc folder.

View HDL Test Bench Files

  • symmetric_fir_tb.vhd: VHDL test bench code, with generated test and output data. If you generated Verilog or SystemVerilog test bench code, the generated file is symmetric_fir_tb.v or

  • symmetric_fir_tb_pkg.vhd: Package file for VHDL test bench code. If you generated SystemVerilog test bench code, the generated file is This file is not generated if you specified Verilog as the target language.

  • symmetric_fir_tb_compile.vhd: Compilation script (vcom commands). This script compiles and loads the entity to be tested (symmetric_fir.vhd) and the test bench code (symmetric_fir_tb.vhd)..

  • Mentor Graphics ModelSim script to initialize the simulator, set up wave window signal displays, and run a simulation.

To view the generated test bench code in the MATLAB Editor, double-click the symmetric_fir_tb.vhd or symmetric_fir_tb.v file in the current folder.

Run Simulation and Verify Generated HDL Code

To verify the simulation results, you can use the Mentor Graphics ModelSim simulator. Make sure that you have already installed Mentor Graphics ModelSim.

To launch the simulator, use the vsim (HDL Verifier) function. This command shows how to open the simulator by specifying the path to the executable:

vsim('vsimdir','C:\Program Files\ModelSim\questasim\10.6b\win64\vsim.exe')

To compile and run a simulation of the generated model and test bench code, use the scripts that are generated by HDL Coder. Following example illustrates the commands that compile and simulate the generated test bench for the sfir_fixed/symmetric_fir subsystem.

  1. Open the Mentor Graphics ModelSim software and navigate to the folder that has the previously generated code files and the scripts.

    QuestaSim>cd C:/work/sl_hdlcoder_work/hdlsrc
  2. Use the generated compilation script to compile and load the generated model and text bench code. Run this command to compile the generated code.

  3. Use the generated simulation script to execute the simulation. The following listing shows the command and responses. You can ignore any warning messages. The test bench termination message indicates that the simulation has run to completion without comparison errors. Run this command to simulate the generated code.


    The simulator optimizes your design and displays the results of simulating your HDL design in a wave window. if you don't see the simulation results, open the wave window. The simulation script displays inputs and outputs in the model including the clock , reset, and clock enable signals in the wave window.

    set of input stimulus and output response from test bench.

You can now view the signals and verify that the simulation results match the functionality of your original design. After verifying, close the Mentor Graphics ModelSim simulator, and then close the files that you have opened in the MATLAB Editor.

See Also


Model Settings

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