Real-Time Workshop User's Guide

Tutorial 2: Data Logging

The Real-Time Workshop MAT-file data logging facility enables a generated program to save system states, outputs, and simulation time at each model execution time step. The data is written to a MAT-file, named (by default) model.mat, where model is the name of your model. In this tutorial, data generated by the model f14rtw is logged to the file f14rtw.mat

To configure data logging, you use the Workspace I/O page of the Simulation Parameters dialog. The process is nearly the same as configuring a Simulink model to save output to the MATLAB workspace. For each workspace return variable you define and enable, the Real-Time Workshop defines a parallel MAT-file variable. For example, if you save simulation time to the variable tout, your generated program logs the same data to a variable named (by default) rt_tout.

In this tutorial, you will modify the f14rtw model such that the generated program saves the simulation time and system outputs to the file f14rtw.mat. Then, you will load the data into the MATLAB workspace and plot simulation time against one of the outputs.

To use the data logging feature:

1. Select the Workspace I/O page of the Simulation Parameters dialog box. The Workspace I/O page specifies how data is loaded from and saved to the workspace.
   
   
2. Check the Time option. Enabling the Time option causes the Real-Time Workshop to generate code that logs the simulation time to the MAT-file matrix rt_tout.
3. Check the Output option. Enabling the Output option causes the Real-Time Workshop to generate code that logs the root Output blocks (Angle of Attack and Pilot G Force) to the MAT-file matrix rt_yout.

The sort order of the rt_yout array is based on the port number of the Outport blocks, starting with 1. Angle of Attack and Pilot G Force will be logged to rt_yout(:,1) and rt_yout(:,2), respectively.

4. If any other options are enabled, uncheck them. Set Decimation to 1 and Format to Array. Then click Apply.
5. Open the Pilot G Force Scope block. To run the model, click on the Start button in the toolbar of the Simulink window. The Scope displays below:

   

6. Verify that the simulation time and Pilot G Force outputs have been correctly saved to the workspace by plotting simulation time versus Pilot G Force.

   plot(tout,yout(:,2))
   

The resultant plot is shown below.

7. The f14rtw program must be rebuilt, because you have changed the model by enabling data logging. Select Build Model from the Real-Time Workshop submenu of the Tools menu in the Simulink window. This is an alternative way to start the Real-Time Workshop build process. It is identical to using Build button in the Simulation Parameters dialog box.
8. When the build concludes, run the executable with the command

   !f14rtw
   

9. The program now produces two message lines, indicating that the MAT-file has been written.

   **starting the model** 
   ** created f14rtw.mat ** 
   

10. Clear the workspace, load the MAT-file data, and look at the workspace variables.

    clear
    load f14rtw.mat
    whos
    

11. Observe that the variables rt_tout (time) and rt_yout (G Force and Angle of Attack) have been loaded from the file. Plot G Force as a function of time.

    plot(rt_tout,rt_yout(:,2))
    

12. The plot should appear identical to the plot you produced in step 5 above.

Tutorial 1: Building a Generic Real-Time Program

Tutorial 3: Code Validation