Fixed-Point Blockset

Simulation Results

Using Simulink and the Fixed-Point Blockset, you can easily transition from a digital controller described in the ideal world of double-precision numbers to one realized in the world of fixed-point numbers. The simulation approach used in this tutorial follows these steps:

• 1. Initial Guess at Scaling. For this tutorial, you run an initial "proof of concept" simulation using a reasonable guess at the fixed-point word size and scaling. This step is included only to illustrate how difficult it is to guess the best scaling.
• 2. Data Type Override. Perform a global override of the fixed-point data types and scaling using double-precision numbers. The maximum and minimum simulation values for each digital controller block are logged to the workspace.
• 3. Automatic Scaling. Use the automatic scaling procedure. This procedure uses the doubles simulation values previously logged to the MATLAB workspace, and changes the scaling for each block that does not have its scaling fixed.

The feedback controller simulation is performed with the Fixed-Point Settings interface. You launch the interface by selecting the FixPt GUI block within the fxpdemo_feedback model, by selecting Fixed-Point settings from the Tools menu in the model window, by right-clicking in the model and selecting Fixed-Point settings from the menu that pops up, or by typing

• fxptdlg('fxpdemo_feedback')
  

at the command line. The three steps of the simulation are described in the following sections. You determine the quality of the simulation results by examining the input and output of the analog plant.

Direct Form Realization

1. Initial Guess at Scaling