Fixed-Point Toolbox™

Using fi Objects with Signal Processing Blockset Software

Reading Fixed-Point Signals from the Workspace

You can read fixed-point data from the MATLAB workspace into a Simulink model using the Signal From Workspace and Triggered Signal From Workspace blocks from Signal Processing Blockset software. Enter the name of the defined fi variable in the Signal parameter of the Signal From Workspace or Triggered Signal From Workspace block.

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Writing Fixed-Point Signals to the Workspace

Fixed-point output from a model can be written to the MATLAB workspace via the Signal To Workspace or Triggered To Workspace block from the blockset. The fixed-point data is always written as a 2-D or 3-D array.

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 Signal To Workspace or Triggered 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 fi object in the MATLAB workspace. You can then use the Signal 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
                Signed: true
            WordLength: 16
        FractionLength: 15

             RoundMode: nearest
          OverflowMode: saturate
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128
         CastBeforeSum: true

The Signal From Workspace block in the following model has these settings:

• Signal — a

• Sample time — 1

• Samples per frame — 2

• Form output after final data value by — Setting to zero

The following parameters in the Solver pane of the Configuration Parameters dialog have these 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

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 Signal To Workspace block dialog. Otherwise, fixed-point data is converted to double and written to the workspace as double.

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

yout =
 

(:,:,1) =

    0.8415   -0.1319
   -0.8415   -0.9561


(:,:,2) =

    1.0504    1.6463
    0.7682    0.3324


(:,:,3) =

   -1.7157   -1.2383
    0.2021    0.6795


(:,:,4) =

    0.3776   -0.6157
   -0.9364   -0.8979


(:,:,5) =

    1.4015    1.7508
    0.5772    0.0678


(:,:,6) =

   -0.5440         0
   -0.5440         0


          DataTypeMode: Fixed-point: binary point scaling
                Signed: true
            WordLength: 17
        FractionLength: 15

             RoundMode: nearest
          OverflowMode: saturate
           ProductMode: FullPrecision
  MaxProductWordLength: 128
               SumMode: FullPrecision
      MaxSumWordLength: 128
         CastBeforeSum: true

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Using the Embedded MATLAB Subset

Using fi Objects with Filter Design Toolbox Software