User manual MATLAB FIXED-POINT TOOLBOX 3

[. . . ] Fixed-Point ToolboxTM 3 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. Fixed-Point ToolboxTM User's Guide © COPYRIGHT 2004­2010 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 following figure shows the Model Explorer when you define the following fimath objects in the MATLAB workspace: F = fimath F= RoundMode: OverflowMode: ProductMode: MaxProductWordLength: SumMode: MaxSumWordLength: nearest saturate FullPrecision 128 FullPrecision 128 G = fimath('OverflowMode', 'wrap') G= RoundMode: OverflowMode: ProductMode: MaxProductWordLength: SumMode: MaxSumWordLength: nearest wrap FullPrecision 128 FullPrecision 128 4-14 fimath Object Properties Select the Base Workspace node in the Model Hierarchy pane to view the current objects in the Contents pane. When you select a fimath object in the Contents pane, you can view and change its properties in the Dialog pane. For more information on working with the Model Explorer, see the following sections of the Fixed-Point Toolbox documentation: · "Specifying Fixed-Point Parameters in the Model Explorer" on page 8-18 · "Sharing Models with Fixed-Point Embedded MATLAB Function Blocks" on page 8-24 4-15 4 Working with fimath Objects Using fimath Properties to Perform Fixed-Point Arithmetic In this section. . . "fimath Rules for Fixed-Point Arithmetic" on page 4-16 "Binary-Point Arithmetic" on page 4-18 "[Slope Bias] Arithmetic" on page 4-22 fimath Rules for Fixed-Point Arithmetic fimath properties define the rules for performing arithmetic operations on fi objects. The fimath properties that govern fixed-point arithmetic operations can come from a fimath object or the global fimath. fimath objects and the global fimath have the following differences: · Individual fi objects can have a local fimath object. fi objects have a local fimath object when you specify fimath properties in a fi constructor or use dot notation to set any fimath object property of a fi object. · The global fimath is the set of fimath properties that fi constructors associate with, and fimath constructors return, when you do not specify any fimath properties in the constructor. When you use the sfi or ufi constructor or when you fail to specify any fimath properties in the fi constructor, the resulting fi object associates itself with the global fimath. See "Working with the Global fimath" on page 4-6 for more information. To determine whether a fi object has a local fimath object or associates with the global fimath, use the isfimathlocal function. The following sections discuss how fi objects with local fimath objects interact with fi objects associated with the global fimath. Binary Operations In binary fixed-point operations such as c = a + b, the following rules apply: · If both a and b associate with the global fimath, the operation uses the global fimath to perform the fixed-point arithmetic. The output fi object c also associates with the global fimath. 4-16 Using fimath Properties to Perform Fixed-Point Arithmetic · If either a or b has a local fimath object, the operation uses that fimath object to perform the fixed-point arithmetic. The output fi object c has the same local fimath object as the input. Unary Operations In unary fixed-point operations such as b = abs(a), the following rules apply: · If a associates with the global fimath, the operation uses the global fimath to perform the fixed-point arithmetic. The output fi object b also associates with the global fimath. · If a has a local fimath object, the operation uses that fimath object to perform the fixed-point arithmetic. The output fi object b has the same local fimath object as the input a. When you specify a fimath object in the function call of a unary fixed-point operation, the operation uses the fimath object you specify to perform the fixed-point arithmetic. For example, when you use a syntax such as b = abs(a, F) or b = sqrt(a, F), the abs and sqrt operations use the fimath object F to compute intermediate quantities. The output fi object b always associates with the global fimath. Concatenation Operations In fixed-point concatenation operations such as c = [a b], c = [a;b] and c = bitconcat(a, b), the following rule applies: · The fimath properties of the left-most fi object in the operation determine the fimath properties of the output fi object c. For example, consider the following scenarios for the operation d = [a b c]: · If a is a fi object associated with the global fimath, the output fi object d also associates with the global fimath. · If a has a local fimath object, the output fi object d has the same local fimath object. [. . . ] 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. 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. [. . . ]