RE: [sv-ac] checker: Clarification on functions & side effects

Hi Ben,

Yes, assignment of a variable that does not belong to the function (i.e., neither its local variable, no argument) is illegal. But if a is a local variable in the function then a++ is legal.

It also turns out that void functions are illegal (or at least, meaningless) in checkers.

Regards,
Dmitry

From: owner-sv-ac@server.eda.org [mailto:owner-sv-ac@server.eda.org] On Behalf Of ben cohen
Sent: Wednesday, September 30, 2009 7:27 PM
To: sv-ac@server.eda.org; Seligman, Erik
Subject: [sv-ac] checker: Clarification on functions & side effects

LRM states that
Functions shall be automatic (or preserve no state information) and have no side effects,

1) What is a side effect? To me a side effect is an assignment of a variable (free variable of the checker or a module).
A function can (in a checker) only return a value.   Thus the following is illegal:
checker t_chk(...);
  logic a, x, y;
 function void inc_a;
       a ++; // same as    a=a+1 // illegal blocking assignment?
     // a <= a+1;  // Illegal also, cannot change value of a variable
   endfunction : a_to_1
 ap_test: assert property(@ (posedge clk) (x, inc_a()) |-> y) ;
endchecker : t_chk
   --
 2) Can functions be of type void in a checker?
   Since a void function must have a side effect, such as assigning a value to a variable, I believe that they are illegal.
Function with return type of void cannot be used in/as an expression.





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