Defining Blocks Using Function Templates - 2022.2 English

While it is common to write functions that accept only a predetermined data type, such as int32, in some cases you might want to create a block that accepts inputs of different sizes, or supports different data types, or create a block that accepts signals with different fixed-point lengths and fractional lengths. To do this you can use a function template that lets you create a block that accepts a variable signal size, data type, or data dimensions.

You can define blocks using function templates, as shown in the following example:

#include <stdint.h>
template <int ROWS, int COLS>
void simple_matrix_add(const int16_t in1[ROWS][COLS],
                       const int16_t in2[ROWS][COLS],
                       int16_t out[ROWS][COLS]) {
   for (int i = 0; i<ROWS; i++) { 
      for (int j = 0; j<COLS; j++) { 
         out[i][j] = in1[i][j] + in2[i][j]; 
      }   
   } 
}

The example uses the template parameters ROWS and COLS. The actual dimensions of the input and output arrays, in1[ROWS][COLS] for instance, are determined at simulation time by the dimensions of the input signals to the block. ROWS and COLS are template parameters used to define the dimensions of the function arguments, and also used in the body of the function, i<ROWS for example.

xmcImportFunction('SimpleLib',{'simple_matrix_add'},...
'template_example.h',{},{},'unlock')

You can perform simple arithmetic operations using template parameters. For example, the following code multiplies the ROWS and COLS of the input matrix to define the output, as shown in the figure below.

#include <stdint.h>
#pragma XMC INPORT in
#pragma XMC OUTPORT out
template<int ROWS,int COLS>
void columnize(const int16_t in[ROWS][COLS], int16_t out[ROWS*COLS]) {
   for (int i = 0; i<ROWS; i++) {
      for (int j = 0; j<COLS; j++) { 
         out[i*COLS+j] = in[i][j];
      }
   }
}

Figure 1. Columnize Function

Other simple supported operations include +, -, *, /, %, <<, and >>, using both the template parameters and integer constants. For example:

template<int M, int N>
void func(const int in[M][N], int out[M*2][M*N]);

template<int ROWS, int COLS>
void func(array[2 * (ROWS + 1) + COLS + 3]);

You can also define a function template that uses a fixed-point data type of variable word length and integer length using function templates, as shown in the following example:

#include <stdint.h>
#include <ap_fixed.h>
#pragma XMC OUTPORT out
template <int WordLen, int IntLen>
void fixed_add(const ap_fixed<WordLen,IntLen> in1, 
                      const ap_fixed<WordLen,IntLen> in2, 
                      ap_fixed<WordLen+1,IntLen> &out) {
   out = in1+in2;
}

xmcImportFunction('SimpleLib',{'fixed_add'},fixed_example.h',{},...
{'$XILINX_VIVADO/include'})