RE: [sv-bc] DataTypes: BNF changes

From: Mark Hartoog (Mark.Hartoog@synopsys.com)
Date: Wed Nov 10 2004 - 14:21:00 PST

  • Next message: Mark Hartoog: "RE: [sv-bc] DataTypes: BNF changes"

    There are some unfortunate corner cases in the syntax for data types
    on wires.

    tri reg w1; // declares a net with tri resolution and reg data type.
    trireg w2; // declares a net with trireg resolution and default (logic)
                // data type.
    trireg reg w3; // declares a net with trireg resolution and reg data type.

    I'm not sure there is anything that can be done about this. I notice at
    one time some of the emails were using a template like syntax:

    tri<reg> w1;
    trireg w2;
    trireg<reg> w3;

    which is syntactically clearer on this point, but I think has other problems.
    Declarations like:

    tri signed [7:0] w1;

    are legal v2k, but "signed [7:0]" is now the data type specifier with
    default logic data type. We can not force <> here for backwards
    compatibility, so it would be funny if

    tri <logic signed [7:0]> w1;

    putting in the default data type now required <>.

    Another alternative would be to outlaw 'reg' data type on wires
    and only allow logic. I don't really like that either.

    Since wire types tri and trireg are not commonly used, I don't expect
    this to be a very serious practical problem, and I guess I would rather
    live with this problem then any of the solutions I can think of.

    Mark Hartoog
    700 E. Middlefield Road
    Mountain View, CA 94043
    650 584-5404
    markh@synopsys.com

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