Verify HDL Model with MATLAB Testbench (Tutorial)

Tutorial Overview

This tutorial guides you through the basic steps for setting up an HDL Verifier application that uses MATLAB to verify a simple HDL design. In this tutorial, you develop, simulate, and verify a model of a pseudorandom number generator based on the Fibonacci sequence. The model is coded in VHDL.

Note   This tutorial demonstrates creating and running a test bench using ModelSim® SE 6.5. If you are not using this version, the messages and screen images from ModelSim may not appear to you exactly as they do in this tutorial. This tutorial requires MATLAB, the HDL Verifier software, and the ModelSim HDL simulator.

In this tutorial, you will perform the following steps:

1. Set up tutorial files.

2. Start MATLAB server.

3. Start ModelSim HDL simulator and set up for cosimulation.

4. Developing the VHDL Code

5. Compile VHDL code.

6. Develop test bench function.

7. Load model for cosimulation.

8. Run simulation.

9. Shut down simulation.

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Setting Up Tutorial Files

To help others have access to copies of the tutorial files, set up a folder for your own tutorial work:

1. Create a folder outside the scope of your MATLAB installation folder into which you can copy the tutorial files. The folder must be writable. This tutorial assumes that you create a folder named MyPlayArea.

2. Copy the following files to the folder you just created:

   matlabroot\toolbox\edalink\extensions\modelsim\modelsimdemos\modsimrand_plot.m
   matlabroot\toolbox\edalink\extensions\modelsim\modelsimdemos\VHDL\modsimrand\
   		modsimrand.vhd
   

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Starting the MATLAB Server

This section describes starting MATLAB, setting up the current folder for completing the tutorial, starting the product's MATLAB server component, and checking for client connections, using shared memory or the server's TCP/IP socket mode. These instructions assume you are familiar with the MATLAB user interface.

Perform the following steps:

1. Start MATLAB.

2. Set your MATLAB current folder to the folder you created in Setting Up Tutorial Files.

3. Verify that the MATLAB server is running by calling function hdldaemon with the 'status' option in the MATLAB Command Window as shown here:

   hdldaemon('status')

   If the server is not running, the function displays

   HDLDaemon is NOT running

   If the server is running in TCP/IP socket mode, the message reads

   HDLDaemon socket server is running on Port portnum with 0 connections

   If the server is running in shared memory mode, the message reads

   HDLDaemon shared memory server is running with 0 connections

   If the server is not currently running, skip to step 5.

4. Shut down the server by typing

   hdldaemon('kill')

   You will see the following message that confirms that the server was shut down.

   HDLDaemon server was shutdown

5. Start the server in TCP/IP socket mode by calling hdldaemon with the property name/property value pair 'socket' 0. The value 0 specifies that the operating system assign the server a TCP/IP socket port that is available on your system. For example

   hdldaemon('socket', 0)

   The server informs you that it has started by displaying the following message. The portnum will be specific to your system:

   HDLDaemon socket server is running on Port portnum with 0 connections

   Make note of portnum as you will need it when you issue the matlabtb command in Loading the Simulation.

   You can alternatively specify that the MATLAB server use shared memory communication instead of TCP/IP socket communication; however, for this tutorial we will use socket communication as means of demonstrating this type of connection. For details on how to specify the various options, see the description of hdldaemon.

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Start ModelSim Simulator and Set Up for Cosimulation

This section describes the basic procedure for starting the ModelSim software and setting up a ModelSim design library. These instructions assume you are familiar with the ModelSim user interface.

Perform the following steps:

1. Start ModelSim from the MATLAB environment by calling the function vsim in the MATLAB Command Window.

   vsim

   This function launches and configures ModelSim for use with the HDL Verifier software. The first folder of ModelSim matches your MATLAB current folder.

2. Verify the current ModelSim folder. You can verify that the current ModelSim folder matches the MATLAB current folder by entering the ls command in the ModelSim command window.

   

   The command should list the files modsimrand.vhd, modsimrand_plot.m, transcript, and compile_and_launch.tcl.

   If it does not, change your ModelSim folder to the current MATLAB folder. You can find the current MATLAB folder by looking in the Current Folder Browser or by viewing the Current folder navigation bar. In ModelSim, you can change the working folder by issuing the command

   cd directory

   Where directory is the folder you want to work from. Or you may also change directory by selecting File > Change Directory....

3. Create a design library to hold your demo compilation results. To create the library and required _info file, enter the vlib and vmap commands as follows:

   ModelSim> vlib work
   
   ModelSim> vmap work work

   

   Note   You must use the ModelSim File menu or vlib command to create the library folder so that the required _info file is created. Do not create the library with operating system commands.

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Developing the VHDL Code

After setting up a design library, typically you would use the ModelSim Editor to create and modify your HDL code. For this tutorial, you do not need to create the VHDL code yourself. Instead, open and examine the existing file modsimrand.vhd. This section highlights areas of code in modsimrand.vhd that are of interest for a ModelSim and MATLAB test bench.

If you choose not to examine the HDL code at this time, skip to Compiling the VHDL File.

You can open modsimrand.vhd in the edit window with the edit command, as follows:

ModelSim> edit modsimrand.vhd

ModelSim opens its edit window and displays the VHDL code for modsimrand.vhd.

While you are viewing the file, note the following:

• The line ENTITY modsimrand contains the definition for the VHDL entity modsimrand:

  ENTITY modsimrand IS
  PORT (
    clk     : IN std_logic ;
    clk_en  : IN std_logic ;
    reset   : IN std_logic ;
    dout    : OUT std_logic_vector (31 DOWNTO 0);
  END modsimrand;

  This is the entity that will be verified in the MATLAB environment during the tutorial. Note the following:

  • By default, the MATLAB server assumes that the name of the MATLAB function that verifies the entity in the MATLAB environment is the same as the entity name. You have the option of naming the MATLAB function explicitly. However, if you do not specify a name, the server expects the function name to match the entity name. In this example, the MATLAB function name is modsimrand_plot and does not match.

  • The entity must be defined with a PORT clause that includes at least one port definition. Each port definition must specify a port mode (IN, OUT, or INOUT) and a VHDL data type that is supported by the HDL Verifier software. For a list of the supported types, see Code HDL Modules for Verification Using MATLAB .

    The entity modsimrand in this example is defined with three input ports clk, clk_en, and reset of type STD_LOGIC and output port dout of type STD_LOGIC_VECTOR. The output port passes simulation output data out to the MATLAB function for verification. The optional input ports receive clock and reset signals from the function. Alternatively, the input ports can receive signals from ModelSim force commands.

    For more information on coding port entities for use with MATLAB, see Code HDL Modules for Verification Using MATLAB .

• The remaining code for modsimrand.vhd defines a behavioral architecture for modsimrand that writes a randomly generated Fibonacci sequence to an output register when the clock experiences a rising edge.

When you are finished examining the file, close the ModelSim edit window.

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Compiling the VHDL File

After you create or edit your VHDL source files, compile them. As part of this tutorial, compile modsimrand.vhd. One way of compiling the file is to click the file name in the project workspace and select Compile > Compile All. An alternative is to specify modsimrand.vhd with the vcom command, as follows:

ModelSim> vcom modsimrand.vhd

If the compilation succeeds, messages appear in the command window and the compiler populates the work library with the compilation results.

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Developing the MATLAB Function

The HDL Verifier software verifies HDL hardware in MATLAB as a function. Typically, at this point you would create or edit a MATLAB function that meets HDL Verifier requirements. For this tutorial, you do not need to develop the MATLAB test bench function yourself. Instead, open and examine the existing file modsimrand_plot.m.

If you choose not to examine the HDL code at this time, skip to Loading the Simulation.

Note   modsimrand_plot.m is a lower-level component of the MATLAB Random Number Generator Demo. Plotting code within modsimrand_plot.m is not discussed in the next section. This tutorial focuses only on those parts of modsimrand_plot.m that are required for MATLAB to verify a VHDL model.

You can open modsimrand_plot.m in the MATLAB Edit/Debug window. For example:

edit modsimrand_plot.m

While you are viewing the file, note the following:

• On line 1, you will find the MATLAB function name specified along with its required parameters:

  function [iport,tnext] = modsimrand_plot(oport,tnow,portinfo)

  This function definition is significant because it represents the communication channel between MATLAB and ModelSim. Note:

  • When coding the function, you must define the function with two output parameters, iport and tnext, and three input parameters, oport, tnow, and portinfo. See MATLAB Function Syntax and Function Argument Definitions.

  • You can use the iport parameter to drive input signals instead of, or in addition to, using other signal sources, such as ModelSim force commands. Depending on your application, you might use any combination of input sources. However, if multiple sources drive signals to a single iport, you will need a resolution function to handle signal contention.

• On lines 22 and 23, you will find some parameter initialization:

  tnext = [];
  iport = struct();

  In this case, function outputs iport and tnext are initialized to empty values.

• When coding a MATLAB function for use with HDL Verifier, you need to know the types of the data that the test bench function receives from and needs to return to ModelSim and how HDL Verifier handles this data; see Data Type Conversions. This function includes the following port data type definitions and conversions:

  • The entity defined for this tutorial consists of three input ports of type STD_LOGIC and an output port of type STD_LOGIC_VECTOR.

  • Data of type STD_LOGIC_VECTOR consists of a column vector of characters with one bit per character.

  • The interface converts scalar data of type STD_LOGIC to a character that matches the character literal for the corresponding enumerated type.

  On line 62, the line of code containing oport.dout shows how the data that a MATLAB function receives from ModelSim might need to be converted for use in the MATLAB environment:

  ud.buffer(cyc) = mvl2dec(oport.dout)

  In this case, the function receives STD_LOGIC_VECTOR data on oport. The function mvl2dec converts the bit vector to a decimal value that can be used in arithmetic computations. Data Type Conversions provides a summary of the types of data conversions to consider when coding your own MATLAB functions.

• Feel free to browse through the rest of modsimrand_plot.m. When you are finished, go to Loading the Simulation.

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Loading the Simulation

After you compile the VHDL source file, you are ready to load the model for simulation. This section explains how to load an instance of entity modsimrand for simulation:

1. Load the instance of modsimrand for verification. To load the instance, specify the vsimmatlab command as follows:

   ModelSim> vsimmatlab modsimrand

   The vsimmatlab command starts the ModelSim simulator, vsim, specifically for use with MATLAB. ModelSim displays a series of messages in the command window as it loads the entity's packages and architecture.

   

2. Initialize the simulator for verifying modsimrand with MATLAB. You initialize ModelSim by using the HDL Verifier matlabtb command. This command defines the communication link and a callback to a MATLAB function that executes in MATLAB on behalf of ModelSim. In addition, the matlabtb command can specify parameters that control when the MATLAB function executes.

   For this tutorial, enter the following matlabtb command:

   > matlabtb modsimrand -mfunc modsimrand_plot -rising /modsimrand/clk -socket portnum

   Arguments in the command line specify the following conditions:

   • modsimrand—Specifies the VHDL module to cosimulate.

   • -mfunc modsimrand_plot—Links an instance of the entity modsimrand to the MATLAB function modsimrand_plot.m. The argument is required because the entity name is not the same as the test bench function name.

   • -rising /modsimrand/clk—Specifies that the test bench function be called whenever signal /modsimrand/clk experiences a rising edge.

   • -socketportnum—Specifies the port number issued with or returned by the call to hdldaemon in Starting the MATLAB Server.

3. Initialize clock and reset input signals. You can drive simulation input signals using several mechanisms, including ModelSim force commands and an iport parameter (see Syntax of a Test Bench Function). For now, enter the following force commands:

   > force /modsimrand/clk 0 0 ns, 1 5 ns -repeat 10 ns
   > force /modsimrand/clk_en 1
   > force /modsimrand/reset 1 0, 0 50 ns

   The first command forces the clk signal to value 0 at 0 nanoseconds and to 1 at 5 nanoseconds. After 10 nanoseconds, the cycle starts to repeat every 10 nanoseconds. The second and third force commands set clk_en to 1 and reset to 1 at 0 nanoseconds and to 0 at 50 nanoseconds.

The ModelSim environment is ready to run a simulation. Now, you need to set up the MATLAB function.

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Running the Simulation

This section explains how to start and monitor this simulation, and rerun it, if you desire. When you have completed as many simulation runs as desired, shut down the simulation as described in the next section.

Running the Simulation for the First Time

Before running the simulation for the first time, you must verify the client connection. You may also want to set breakpoints for debugging.

Perform the following steps:

1. Open ModelSim and MATLAB windows.

2. In MATLAB, verify the client connection by calling hdldaemon with the 'status' option:

   hdldaemon('status')

   This function returns a message indicating a connection exists:

   HDLDaemon socket server is running on port 4795 with 1 connection

   Or

   HDLDaemon shared memory server is running with 1 connection

   Note   If you attempt to run the simulation before starting the hdldaemon in MATLAB, you will receive the following warning: #ML Warn - MATLAB server not available (yet), The entity 'modsimrand' will not be active

3. Open modsimrand_plot.m in the MATLAB Edit/Debug window.

4. Search for oport.dout and set a breakpoint at that line by clicking next to the line number. A red breakpoint marker will appear.

5. Return to ModelSim and enter the following command in the command window:

    > run 80000
   

   This command instructs ModelSim to advance the simulation 80,000 time steps (80,000 nanoseconds using the default time step period). Because you previously set a breakpoint in modsimrand_plot.m, however, the simulation runs in MATLAB until it reaches the breakpoint.

   ModelSim is now blocked and remains blocked until you explicitly unblock it. While the simulation is blocked, note that MATLAB displays the data that ModelSim passed to the MATLAB function in the Workspace window.

   

   In ModelSim, an empty figure window opens. You can use this window to plot data generated by the simulation.

6. Examine oport, portinfo, and tnow by hovering over these arguments inside the MATLAB Editor. Observe that tnow, the current simulation time, is set to 0. Also notice that, because the simulation has reached a breakpoint during the first call to modsimrand_plot, the portinfo argument is visible in the MATLAB workspace.

7. Click Debug > Continue in the MATLAB Edit/Debug window. The next time the breakpoint is reached, notice that portinfo no longer appears in the MATLAB workspace. The portinfo function does not show because it is passed in only on the first function invocation. Also note that the value of tnow advances from 0 to 5e-009.

8. Clear the breakpoint by clicking the red breakpoint marker.

9. Unblock ModelSim and continue the simulation by clicking Debug > Continue in the MATLAB Edit/Debug window.

   The simulation runs to completion. As the simulation progresses, it plots generated data in a figure window. When the simulation completes, the figure window appears as shown here.

   

The simulation runs in MATLAB until it reaches the breakpoint that you just set. Continue the simulation/debugging session as desired.

Rerunning the Simulation

If you want to run the simulation again, you must restart the simulation in ModelSim, reinitialize the clock, and reset input signals. To do so:

1. Close the figure window.

2. Restart the simulation with the following command:

   > restart

   The Restart dialog box appears. Leave all the options enabled, and click Restart.

   Note   The Restart button clears the simulation context established by a matlabtb command. Thus, after restarting ModelSim, you must reissue the previous command or issue a new command.

3. Reissue the matlabtb command in the HDL simulator.

   > matlabtb modsimrand -mfunc modsimrand_plot -rising /modsimrand/clk -socket portnum

4. Open modsimrand_plot.m in the MATLAB Edit/Debug window.

5. Set a breakpoint at the same line as in the previous run.

6. Return to ModelSim and re-enter the following commands to reinitialize clock and input signals:

   > force /modsimrand/clk 0 0,1 5 ns -repeat 10 ns
   > force /modsimrand/clk_en 1
   > force /modsimrand/reset 1 0, 0 50 ns

7. Enter a command to start the simulation, for example:

   > run 80000

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Shutting Down the Simulation

This section explains how to shut down a simulation in an orderly way.

In ModelSim, perform the following steps:

1. Stop the simulation on the client side by selecting Simulate > End Simulation or entering the quit command.

2. Quit ModelSim.

In MATLAB, you can just quit the application, which will shut down the simulation and also close MATLAB.

To shut down the server without closing MATLAB, you have the option of calling hdldaemon with the 'kill' option:

hdldaemon('kill')

The following message appears, confirming that the server was shut down:

HDLDaemon server was shutdown

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Stop Test Bench Simulation

HDL Cosimulation Using MATLAB Component Function

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