RE: [sv-ac] checker: why is range not bounded by constant expression, like in modules?

Hi Ben,

I think that as in sequences and properties, the validity of the argument can only be ascertained once it is substituted in place of a reference to the corresponding formal argument. It cannot be decided at the checker port level only. This is the diff with parameters in everything else but checkers. I still think that we should have preserved the form how parameters are specified on everything else. It would make checking simpler not only for the compiler but also for the user.

Thanks
ed

From: Ben Cohen [mailto:hdlcohen@gmail.com]
Sent: Tuesday, May 22, 2012 2:11 PM
To: sv-ac@eda-stds.org; Korchemny, Dmitry; Seligman, Erik; Eduard Cerny
Subject: [sv-ac] checker: why is range not bounded by constant expression, like in modules?

ISSUE: In a checker, a formal argument can define a range, which can be used in an assertion.
The actual for that range can be 1) a constant (e.g., 2, 3, or $); 2) a variable (TRUE??)
See the example below and module top.
[Ben] Where does it state that the actual argument that corresponds to a range has to be a constant? seems like it should be. The way I read the LRM, the actual could be a variable, as shown in my example in module "top".

LRM 17.3 Checker instantiation
As in the case of sequences and properties, if $ is an actual input argument to a checker instance,
then the corresponding formal argument shall be untyped and each of its references either shall be an
upper bound in a cycle_delay_const_range_expression or shall itself be an actual argument in an
instance of a named sequence or property, or in a checker instance"

checker chkr_c_test (
        input logic clk, a, b, d,
        input int min,
        input int max); // must be untyped if actual is a continuous assignment
    ap_ok_in_a_checker: assert property(@ (posedge clk)
       a |-> ##[min:max] b); // illegal in a module, legal in a checker
endchecker: chkr_c_test

module m_c_test #(mn=0, mx=20) (
        input logic clk, a, b, d,
        input int min,
        input int max); // must be untyped if actual is a continuous assignment
    ap_error_in_a_module: assert property(@ (posedge clk)
       a |-> ##[min:max] b); // illegal in a module, legal in a checker
       // Range must be bounded by constant expressions.

    ap_ok_in_module: assert property(@ (posedge clk) // using parameters
        a |-> ##[mn:mx] b);
endmodule: m_c_test

module top;
    bit clk, a=1, b=1, d;
    int min=2, max=10;
    initial forever #10 clk=!clk;
    default clocking cb_clk @ (posedge clk); endclocking

    chkr_c_test c1(clk, a, b, d, min, max); // Instance of a checker
   // SEEMS LIKE min and max sould be constants and not variables

    initial begin
      ##1 min=1; max=20;
      ##5 min=4; max=9;
    end

endmodule : top

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