FFT Static Parameters - 2021.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
UG1399
ft:locale
English (United States)
Release Date
2021-12-15
Version
2021.2 English

The static parameters of the FFT define how the FFT is configured and specifies the fixed parameters such as the size of the FFT, whether the size can be changed dynamically, whether the implementation is pipelined or radix_4_burst_io.

The hls_fft.h header file defines a struct hls::ip_fft::params_t which can be used to set default values for the static parameters. If the default values are to be used, the parameterization struct can be used directly with the FFT function.

hls::fft<hls::ip_fft::params_t >  
    (xn1, xk1, &fft_status1, &fft_config1);

A more typical use is to change some of the parameters to non-default values. This is performed by creating a new user-defined parameterization struct based on the default parameterization struct and changing some of the default values.

In the following example, a new user struct my_fft_config is defined with a new value for the output ordering (changed to natural_order). All other static parameters to the FFT use the default values.

struct my_fft_config : hls::ip_fft::params_t {
    static const unsigned ordering_opt = hls::ip_fft::natural_order;
};

hls::fft<my_fft_config >  
     (xn1, xk1, &fft_status1, &fft_config1);

The values used for the parameterization struct hls::ip_fft::params_t are explained in FFT Struct Parameters. The default values for the parameters and a list of possible values are provided in FFT Struct Parameter Values.