Automatically change scaling of fixed-point data types
autofixexp script automatically changes
the scaling for model objects that specify fixed-point data types.
However, if an object's Lock output data type setting against
changes by the fixed-point tools parameter is selected,
the script refrains from scaling that object.
This script collects range data for model objects, either from design minimum and maximum values that objects specify explicitly, or from logged minimum and maximum values that occur during simulation. Based on these values, the tool changes the scaling of fixed-point data types in a model so as to maximize precision and cover the range.
You can specify design minimum and maximum values for model
objects using parameters typically titled Output minimum and Output
maximum. See Blocks That Allow Signal Range Specification (Simulink) for a
list of Simulink® blocks that permit you to specify these values.
In the autoscaling procedure that the
executes, design minimum and maximum values take precedence over the
If you intend to scale fixed-point data types using simulation
minimum and maximum values, the script yields meaningful results when
exercising the full range of values over which your design is meant
to run. Therefore, the simulation you run prior to using
simulate your design over its full intended operating range. It is
especially important that you use simulation inputs with appropriate
speed and amplitude profiles for dynamic systems. The response of
a linear dynamic system is frequency dependent. For example, a bandpass
filter will show almost no response to very slow and very fast sinusoid
inputs, whereas the signal of a sinusoid input with a frequency in
the passband will be passed or even significantly amplified. The response
of nonlinear dynamic systems can have complicated dependence on both
the signal speed and amplitude.
If you already know the simulation range you need to cover,
you can use an alternate autoscaling technique described in the
fixptbestprec reference page.
To control the parameters associated with automatic scaling, such as safety margins, use the Fixed-Point Tool.
To learn how to use the Fixed-Point Tool, refer to Propose Fraction Lengths Using Simulation Range Data.