Packaging up code using functions

Often, we'll have code that we will be reusing within the same module or that's common to a group of modules. We can package this code up in a function:

function [4:0] func_addr_decode(input [31:0] addr);
  func_addr_decode = '0;
  for (int i = 0; i < 32; i++) begin
    if (addr[i]) begin
      return(i);
    end
  end
endfunction

Here, we created a function called func_addr_decode that returns a 5-bit value. function takes a 32-bit input called address. Functions can have multiple outputs, but we will not be using this feature. To return the function's value, you can assign the result to the function name or use the return statement.

Creating combinational logic

The two main ways of creating logic are via assign statements and always blocks. assign statements are convenient when creating purely combinational logic...