Creating the Vitis IP

Scalar Function Example

Similar to the basic logic examples, we will illustrate the IP with a simple scalar function of two inputs a and b.

The files for the project are in the directory hwdesign/demos/scalar_fun/scalar_fun_vitis. In the directory scalar_fun_vitis/src/, there is the main source C file, scalar_fun.cpp describing the functionality for our “IP”:

    void simp_fun(int a, int b, int& c) {
        #pragma HLS INTERFACE s_axilite port=a
        #pragma HLS INTERFACE s_axilite port=b
        #pragma HLS INTERFACE s_axilite port=c
        #pragma HLS INTERFACE s_axilite port=return
        c = a * b;
        }

The function just multiplies two numbers. You can change this as you like. This file is already in the git repo, so you do not need to write it.

A Simple Testbench

A testbench is a program that tests the IP, generally by giving it inputs and verifying the outputs match the expected results. In this case, the testbench is in the directory scalar_fun_vitis/testbench/tb_scalar_fun.cpp. The code looks like:

    int main() {
      int c;
      int a = 7;
      int b = 5;
      int c_exp = a*b;
      simp_fun(a, b, c);
      std::cout << "Result: " << c << std::endl;

      if (c == c_exp)
          std::cout << "Test passed!" << std::endl;
      else
          std::cout << "Test failed!" << std::endl;
          
      return 0;
  }

So, it basically gives the IP two numbers and tests the result matches. Later, we will create more elaborate tests.

Creating a Vitis HLS Project

To simulate this simple IP and testbench, follow the instructions to create a Vitis HLS project with the files:

• Top Function: simp_fun
• Design Files: Add src/scalar_fun.cpp
• Testbench: Add testbench/scalar_fun.cp

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Go to Simulate and synthesize the IP