Variable length types in tasks and fucntions

OVM
1

hi,
i was trying to write a simple adder function/task,which will take the length of inputs as an argument and then accordingly add them.

the code looks like this
function void add(input int len=8,input logic [len-1:0] a,input logic[len-1:0]b,output logic[len-1:0] sum);

but my compiler(Riviera-Pro) gives an error that lenshould be a constant.
i want to make a generic adder ,how can it be done?
i am using system verilog.
thanks in advance.
waris

2

In vectors you cannot use varaiable lengths, they should be constant, so to make them generic you need to define this constant using “parameter” or `define.

3

thanks for the reply.
i have tried that also.
but here also some errors are coming.
can you please give an example.
i know how to use parameters in a module but,i want to use this in a function.
any suggestions are welcome.

4

parameters in function works similar to modules.
example

parameter length = 8;

function void add (input [(length -1) : 0] a,b, output [(length-1) : 0] sum);
--------- logic -------
endfunction : add

this should work, as this worked for me on modelsim

5

Hi, can we write parameterized task/function in systemverilog like template function in C++? Or it can be implemented using parameterized class in which parameterized task/function can be used? Is that right?

6

hi,
sushil thanks for ur reply.i will try it .
Ichip can you plz explain the meaning of your post???

7

This is a frequently requested enhancement to Verilog/SystemVerilog. What you can do today is create a parametrized virtual class, and declare a static function/task inside the class.

virtual class C #(type T= int);
  static function T add(T a, T b);
    return (a+b);
  endfunction
endclass

typedef bit [7:0] data_t;
typedef bit [15:0] address_t;

data_t  X,Y,Z;
address_t A,B,C;
...
      Z = C#(data_t)::add(X,Y);
      C = C#(type(C))::add(A,B);

Dave Rich

The staticis so that you don’t have to construct a class object to use the task, and the virtual is so no one is allowed to construct the class.