Major advantage of function over task

The function can return the value and task cannot return the value.

What is the return value?

The user called the method, it will execute lines of code.
On completion of method definition method return some value.

How can the function return value?

The return type should be mention in the function definition. Need to use of return keyword.

What is advantage/application to return value?

Many times a user needs to use the same condition multiple times.

Can function return 'x' or 'z'?
- Yes, function can return 'x' or 'z', need to use logic return type in function.

What is preferable task or function?

- Depends on the application user will decide to use task or function.

USER WANT CODE:

function logic hello(bit x);

$display("This is Hello function");

if(x == 1)

begin

  return 1'hz; // return 'z' or 'x' state

end

endfunction

task Hi();

//##1;

int a;

a = 1;

$display("This is Hi task");

hello(a);

endtask

module top();

logic a;

initial

begin

Hi();

a = 1;

if(hello(a) === 1'hz) // '===' require for z or x comparison

begin

  $display("I am good");

end

else

begin

  $display("Good bye");

end

end

endmodule

Link: https://www.edaplayground.com/x/69ES

Difference between task and function

To reuse the same lines of code again and again methods are used. System Verilog supports two types of methods.
(1) Function
(2) Task

Function:
- Delayed can NOT use in the function.
- Task WITHOUT delay can call in the function. It shouts only WARNING, not an ERROR.
- The function calls another function.
- The function can return value.

Task:
- Delayed can be inserted in the task.
- The task with DELAY can be called in the task.
- The function also can call in the task.
- The task can NOT return value.

The user can NOT call a task in function. Is it true? Is it shouts an ERROR?
NOT ALWAYS. The user can call a task in function if the definition of a task should NOT contain delay.

WITHOUT delay Warning: "warning-[teif] Task enabled inside a function"

WITH delay Error: "Function "function_name" has illegal use of delay or synchronization"


USER WANT CODE:

function hello();

  $display("This is Hello function");

  Hi(); // CALL TASK(without delay) INSIDE FUNCTION

endfunction

task Hi();

  //#1;  // without delay

  $display("This is Hi task");

  hello();

endtask

module top();

initial

   begin

     hello(); // Call function

     //Hi(); // call task

   end

endmodule

To run simulation click on below link:
Link: https://www.edaplayground.com/x/2uZ8