Using fi Objects with Simulink

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Reading Fixed-Point Data from the Workspace Writing Fixed-Point Data to the Workspace Setting the Value and Data Type of Block Parameters Logging Fixed-Point Signals Accessing Fixed-Point Block Data During Simulation

Reading Fixed-Point Data from the Workspace

You can read fixed-point data from the MATLAB workspace into a Simulink model via the From Workspace block. To do so, the data must be in a structure format with a fi object in the values field. In array format, the From Workspace block only accepts real, double-precision data.

To read in fi data, the Interpolate data parameter of the From Workspace block must not be selected, and the Form output after final data value by parameter must be set to anything other than Extrapolation.

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Writing Fixed-Point Data to the Workspace

You can write fixed-point output from a model to the MATLAB workspace via the To Workspace block in either array or structure format. Fixed-point data written by a To Workspace block to the workspace in structure format can be read back into a Simulink model in structure format by a From Workspace block.

Note   To write fixed-point data to the MATLAB workspace as a fi object, select the Log fixed-point data as a fi object check box on the To Workspace block dialog. Otherwise, fixed-point data is converted to double and written to the workspace as double.

For example, you can use the following code to create a structure in the MATLAB workspace with a fi object in the values field. You can then use the From Workspace block to bring the data into a Simulink model.

a = fi([sin(0:10)' sin(10:-1:0)'])
 
a =
 
         0   -0.5440
    0.8415    0.4121
    0.9093    0.9893
    0.1411    0.6570
   -0.7568   -0.2794
   -0.9589   -0.9589
   -0.2794   -0.7568
    0.6570    0.1411
    0.9893    0.9093
    0.4121    0.8415
   -0.5440         0


          DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 16
        FractionLength: 15
 
s.signals.values = a

s = 

    signals: [1x1 struct]

s.signals.dimensions = 2

s = 

    signals: [1x1 struct]

s.time = [0:10]'

s = 

    signals: [1x1 struct]
       time: [11x1 double]

The From Workspace block in the following model has the fi structure s in the Data parameter.

Remember, to write fixed-point data to the MATLAB workspace as a fi object, select the Log fixed-point data as a fi object check box on the To Workspace block dialog. Otherwise, fixed-point data is converted to double and written to the workspace as double.

In the model, the following parameters in the Solver pane of the Configuration Parameters dialog have the indicated settings:

• Start time — 0.0

• Stop time — 10.0

• Type — Fixed-step

• Solver — Discrete (no continuous states)

• Fixed step size (fundamental sample time) — 1.0

  

The To Workspace block writes the result of the simulation to the MATLAB workspace as a fi structure.

simout.signals.values
 
ans =
 
         0   -8.7041
   13.4634    6.5938
   14.5488   15.8296
    2.2578   10.5117
  -12.1089   -4.4707
  -15.3428  -15.3428
   -4.4707  -12.1089
   10.5117    2.2578
   15.8296   14.5488
    6.5938   13.4634
   -8.7041         0


DataTypeMode: Fixed-point: binary point scaling
            Signedness: Signed
            WordLength: 32
        FractionLength: 25

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Setting the Value and Data Type of Block Parameters

You can use Fixed-Point Toolbox expressions to specify the value and data type of block parameters in Simulink. Refer to Block Support for Data and Numeric Signal Types in the Simulink documentation for more information.

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Logging Fixed-Point Signals

When fixed-point signals are logged to the MATLAB workspace via signal logging, they are always logged as fi objects. To enable signal logging for a signal, select the Log signal data option in the signal's Signal Properties dialog box. For more information, refer to Exporting Signal Data Using Signal Logging in the Simulink documentation.

When you log signals from a referenced model or Stateflow^® chart in your model, the word lengths of fi objects may be larger than you expect. The word lengths of fixed-point signals in referenced models and Stateflow charts are logged as the next largest data storage container size.

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Accessing Fixed-Point Block Data During Simulation

Simulink provides an application program interface (API) that enables programmatic access to block data, such as block inputs and outputs, parameters, states, and work vectors, while a simulation is running. You can use this interface to develop MATLAB programs capable of accessing block data while a simulation is running or to access the data from the MATLAB command line. Fixed-point signal information is returned to you via this API as fi objects. For more information on the API, refer to "Accessing Block Data During Simulation" in the Simulink documentation.

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Interoperability with Other Products

Using fi Objects with DSP System Toolbox

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