Subject: 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
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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