MATLAB: How to set an FI object in MATLAB using Fixed-Point Toolbox to match the default fi object in Simulink

simulink

I would like to use the FI command to set the data within Simulink, but the default fi object created in Simulink has different properties than the default Fixed-Point Toolbox fi object. How can I match their properties?

Best Answer

Simulink has some default options for a fi object. There is no automatic way of creating a new fi object in MATLAB to the Simulnk specification.

As workaround, specify the following properties when creating a fi object in MATLAB:

 RoundMode: 'floor'
 Overflow: 'wrap'
 ProductMode: 'keeplsb'
 SumMode: 'keeplsb'

Related Solutions

MATLAB: How to change the word length of a fi object with the Fixed-Point Toolbox 1.1 (R14SP1)

This enhancement has been incorporated in Release 2008a (R2008a). For previous product releases, read below for any possible workarounds:

In order to change the word length of a fi object, it is necessary to create a new fi object with the value of the original object, as in the example below.

a = fi(3);
b = fi(4);
F = fimath;
F.MaxProductWordLength = 32;
c = F.mpy(a,b);
%note that at this point, c has a word length of 32
c = fi(c,1,16);
%creates a new fixed-point object with the same properties as c, but with a word length of 16

MATLAB: Is the fixed-point number’s FractionLength value greater than its WordLength value

The terminology used in fixed-point math can be confusing, but it looks like there is nothing wrong with the FractionLength value, as it is not measured in terms of number of bits. The documentation at the following location discusses scaling of fixed-point values:

 <http://www.mathworks.com/access/helpdesk/help/toolbox/fixedpoint/ug/f6389.html>

"fraction length" is defined to be the negative of the fixed exponent value. Thus, even though we are dealing with a 16-bit word length, there is no requirement for the fraction length to be less than 16.

The documentation at the following location discusses the concept of fraction length that is greater than word length or negative.

 <http://www.mathworks.com/access/helpdesk/help/toolbox/filterdesign/index.html?/access/helpdesk/help/toolbox/filterdesign/ug/f8-109180.html>

Under the secton titled Property Details for Fixed Point Filter, there is a sub-section titled Notes About Fraction Length, Word Length, and Precision.

Best Answer

Related Solutions

MATLAB: How to change the word length of a fi object with the Fixed-Point Toolbox 1.1 (R14SP1)

MATLAB: Is the fixed-point number’s FractionLength value greater than its WordLength value

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