System Objects in DSP System Toolbox that Support Fixed-Point Design - MATLAB & Simulink (original) (raw)
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Get Information About Fixed-Point System Objects
System objects that support fixed-point data processing have fixed-point properties. When you display the properties of a System object™, click show all properties at the end of the property list to display the fixed-point properties for that object. You can also display the fixed-point properties for a particular object by typingdsp.<ObjectName>.helpFixedPoint at the MATLAB® command line.
DSP System Toolbox System Objects That Support Fixed Point
Set System Object Fixed-Point Properties
Several properties affect the fixed-point data processing used by a System object. Objects perform fixed-point processing and use the current fixed-point property settings when they receive fixed-point input.
You change the values of fixed-point properties in the same way as you change any System object property value. See Configure Components. You also use the Fixed-Point Designer™numerictype (Fixed-Point Designer) object to specify the desired data type as fixed-point, the signedness, and the word- and fraction-lengths. System objects support these values ofDataTypeMode: Boolean,Double, Single, and Fixed-point: binary point scaling.
In the same way as for blocks, the data type properties of many System objects can set the appropriate word lengths and scalings automatically by using full precision. System objects assume that the target specified on the Configuration Parameters Hardware Implementation target is ASIC/FPGA.
If you have not set the property that activates a dependent property and you attempt to change that dependent property, a warning message displays. For example, for the dsp.FFT object, before you setCustomOutputDataType tonumerictype(1,32,30), setOutputDataType to 'Custom'.
Note
System objects do not support fixed-point word lengths greater than 128 bits.
For any System object provided in the Toolbox, the fimath settings for any fimath attached to a fi input or a fi property are ignored. Outputs from a System object never have an attached fimath.
Full Precision for Fixed-Point System Objects
FullPrecisionOverride is a convenience property that, when you set to true, automatically sets the appropriate properties for an object to use full-precision to process fixed-point input. For System objects, full precision, fixed-point operation refers to growing just enough additional bits to compute the ideal full precision result. This operation has no minimum or maximum range overflow nor any precision loss due to rounding or underflow. It is also independent of any hardware-specific settings. The data types chosen are based only on known data type ranges and not on actual numeric values. Full precision for System objects does not optimize coefficient values.
When you set the FullPrecisionOverride property totrue, the other fixed-point properties it controls no longer apply and any of their non-default values are ignored. These properties are also hidden. To specify individual fixed-point properties, first setFullPrecisionOverride to false.