User manual MATLAB SIMULINK FIXED POINT 6

[. . . ] Simulink® Fixed PointTM 6 User's Guide How to Contact The MathWorks Web Newsgroup www. mathworks. com/contact_TS. html Technical Support www. mathworks. com comp. soft-sys. matlab suggest@mathworks. com bugs@mathworks. com doc@mathworks. com service@mathworks. com info@mathworks. com Product enhancement suggestions Bug reports Documentation error reports Order status, license renewals, passcodes Sales, pricing, and general information 508-647-7000 (Phone) 508-647-7001 (Fax) The MathWorks, Inc. 3 Apple Hill Drive Natick, MA 01760-2098 For contact information about worldwide offices, see the MathWorks Web site. Simulink® Fixed PointTM User's Guide © COPYRIGHT 1995­2010 by The MathWorks, Inc. The software described in this document is furnished under a license agreement. The software may be used or copied only under the terms of the license agreement. [. . . ] The Autoscale Information dialog box appears. 6-14 Working with the Fixed-Point Tool Fixed-Point Tool Workflow 5. 2 If you do not want to accept the proposal for a result, uncheck the Accept checkbox in the Fixed-Point Tool Contents pane for that result. Click the Apply accepted fraction lengths button proposed data types to the model. to write the 5. 3 Note If you have not fixed all the warnings in the model, the Fixed-Point Tool displays the Apply Fraction Length Warning dialog box. Store Reference Run 6. 1 Click the Exchange Active and Reference Results button to store the ideal doubles-based simulation in the reference group. This prevents the tool from overwriting results that you want to retain. In the Fixed-Point Tool Model Hierarchy pane, select the system or subsystem for which you want a proposal. Change Data type override to Use local settings. This option enables each of the model's subsystems to use its locally specified data type settings. Verify that Fixed-point instrumentation mode is set to Minimums, maximums and overflows. 7. Verify new settings 7. 1 7. 2 7. 3 7. 4 7. 5 Click the Fixed-Point Tool Start button to run the simulation. Compare the ideal results stored in the reference run with the fixed-point results in the active run: · In the Contents pane, select a result that has logged signal data. These results are annotated with the icon. · Click the Time Series Difference (A-R) Plot to view the difference between the active and reference runs for the selected result 6-15 6 Fixed-Point Tool Prerequisites for Using the Fixed-Point Tool To use the Fixed-Point Tool to generate scaling proposals for your model, you must first set up your model in Simulink. 1 Open your model in Simulink. 2 Select Simulation > Normal in the Simulink menu to ensure the model runs in Normal mode. Note The Fixed-Point Tool supports only Normal mode. 3 If you are using design minimum and maximum range information, add this information to blocks. You specify a design range for model objects using parameters typically titled Output minimum and Output maximum. See "Blocks That Allow Signal Range Specification" in Simulink User's Guide for a list of blocks that permit you to specify these values. 4 Specify fixed-point data types for blocks and signals in your model. For blocks with the Data Type Assistant, use the Calculate Best-Precision Scaling button to calculate best-precision scaling automatically. For more information, see "Specifying Fixed-Point Data Types with the Data Type Assistant" on page 1-24. Note If you have a floating-point model, use the Fixed-Point Advisor to facilitate converting your model to an equivalent fixed-point representation. To learn more about the Fixed-Point Advisor, see Chapter 5, "Fixed-Point Advisor". 5 You can choose to lock some blocks against autoscaling by selecting the Lock output data type setting against changes by the fixed-point tools parameter. If an object's Lock output data type setting against changes by the fixed-point tools parameter is selected, the tool does not propose scaling for that object. 6-16 Working with the Fixed-Point Tool 6 Select Update Diagram from the Simulink Edit menu to perform parameter range checking for all blocks in the model. Running the Model to Gather a Floating-Point Benchmark You first run the model with a global override of the fixed-point data types using double-precision numbers to avoid quantization effects. This provides a floating-point benchmark that represents the ideal output. [. . . ] It can also be used with all the standard data type access methods in simstruc. h, such as ssGetDataTypeSize. Use this function if you want to register a scaled double data type. Alternatively, you can use one of the other fixed-point registration functions: · Use ssRegisterDataTypeFxpBinaryPoint to register a data type with binary-point-only scaling. · Use ssRegisterDataTypeFxpFSlopeFixExpBias to register a data type with [Slope Bias] scaling by specifying the word length, fractional slope, fixed exponent, and bias. [. . . ]