Prepare the Kernels - 2022.2 English

Kernels are computation functions that form the fundamental building blocks of the data flow graph specifications. Kernels are declared as ordinary C/C++ functions that return void and can use special data types as arguments (discussed in Window and Streaming Data API). Each kernel must be defined in its own source file. This organization is recommended for reusability and faster compilation. Furthermore, the kernel source files should include all relevant header files to allow for independent compilation.

It is recommended that a header file (kernels.h in this documentation) should declare the function prototypes for all kernels used in a graph. An example is as follows.

#ifndef FUNCTION_KERNELS_H
#define FUNCTION_KERNELS_H

void simple(input_window<cint16> * in, output_window<cint16> * out);

#endif

In the example, the #ifndef and #endif are present to ensure that the include file is only included once, which is good C/C++ practice.

The kernels.cc is the implementation file for the simple function. The kernel implementation declares two complex int 16 variables c1 and c2. It then reads the complex int16 input data into c1 using the window_readincr API, adds the real and imaginary values and assigns it back to c2.real. It also subtracts the imaginary value from the real value and assign it to c2.imag. Finally c2 is written back to the output window using the window_writeincr API.

/* A simple kernel */
#include <adf.h>
#include "include.h"

void simple(input_window<cint16> * in, output_window<cint16> * out) {
  cint16 c1, c2;

  for (unsigned i=0; i<NUM_SAMPLES; i++) {
    c1 = window_readincr(in);
    c2.real = c1.real+c1.imag;
    c2.imag = c1.real-c1.imag;
    window_writeincr(out, c2);
  }
}