Re: [sv-bc] Re: implicit instantiation of top-level modules?

From: Michael McNamara (mac@verisity.com)
Date: Thu Jul 10 2003 - 17:44:52 PDT

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    Steven Sharp writes:
    >
    > >X-Authentication-Warning: max.boyd.com: majordomo set sender to
    > owner-etf@boyd.com using -f
    > >From: Michael McNamara <mac@verisity.com>
    >
    > > Actually, what this allows is an additional fairly powerfull
    > > capability: Easy reference to a sibling.
    >
    > > The difference here is that the add_jtag doesn't need to know the
    > > instance name of the ff it is mucking with: the rules of 12.4 require
    > > the simulator to find the nearest neighbor up the hierarchy that
    > > instanticate an 'ff' module. It does not affect every 'ff' module,
    > > just the first one found using the upwards relative refernecing rules
    > > defined in 12.4.1
    >
    > This does not work. Module names will only match ancestors. To match
    > a sibling requires using an instance name. Note that with an ancestor,
    > there is a unique match for the module name. There could be multiple
    > siblings that were instances of the same module.
    >
    > What this allows is a reference to something in a parent or other
    > ancestor without needing to know the instance name that that parent
    > got instantiated with.
    >

    Memo to self: quit posting code snippets from places where you don't
    have the ability to present the code first to a tool to check syntax
    before annoying one's colleagues with the code.

    Of course what I meant to code was:

    module jtag_ff(D, CLK, JTAG_D, JTAG_C, Q, Q_);
       input D, CLK, JTAG_D, JTAG_C;
       output Q, Q_;
       ff flip_flop (D, CLK, Q, Q_);
       add_jtag jt (JTAG_D, JTAG_C);
    endmodule

    module add_jtag(JTAG_D, JTAG_C);
       input JTAG_D, JTAG_C;
       always @(JTAG_C) jtag_ff.flip_flop.Q = JTAG_D;
    endmodule // add_jtag

    module ff (D, CLK, Q, Q_);
       input D, CLK;
       output Q, Q_;
       reg Q;
       always @(CLK) Q = D;
       assign Q_ = ~Q;
    endmodule // ff

    where indeed, this feature allows one to refer to a sibling, by using
    one's parent's MODULE NAME followed by the sibling's INSTANCE NAME
    rather than needing to know one's parents INSTANCE NAME.

    Without this feature such creation of a jtag_ff would be
    uninstantiable (more than once).

    -mac

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