Re: $mfactor in Verilog-style netlists

Geoffrey.Coram wrote:

>In the conference call yesterday (minutes coming soon),
>we agreed that
>a) we need a multiplicity factor
>b) the simulator should handle all the "easy" rules
> automatically (scale "through" contributions by m,
> "through" sensors by 1/m, etc.)
>c) mismatch and "rmin" are tough to handle automatically,
> so give access to the multiplicity for an instance
> through the function $mfactor
>d) A model writer generally shouldn't use $mfactor, except
> perhaps to scale "output parameters," and the simulator
> should issue a warning if a contribution depends
> explicitly on $mfactor. (Colin will have to live with
> these warnings, or get his simulator to switch it off.)
>e) For those Spice-like simulators that have an instance
> parameter for the multiplicity factor, eg "m", in a
> Spice netlist, this should be translated automatically
> (such that $mfactor returns the correct value and the
> rules in (b) are applied.
>
>So, the missing piece is: how in a Verilog netlist does
>one specify the multiplicity? Take the instance line
> bsim5 #(.l(90n),.w(1u),.type("nmos")) mn1(.d(d),.g(g),.s(s),.b(b))
>How do we make 5 in parallel?
>
>We could allow .$mfactor(5) in the parameter list, but only
>because we're using named overrides, and the $things aren't
>supposed to be assigned to.
>
>We could put
> bsim5 #(.l(90n),.w(1u),.type("nmos");5) mn1(.d(d),.g(g),.s(s),.b(b))
>
>
>Someone asked about the range item for an instance, I think
>that would look like this:
> bsim5 #(.l(90n),.w(1u),.type("nmos")) mn[1:5](.d(d),.g(g),.s(s),.b(b))
>Am I reading the BNF right? Doesn't this mean 5 instances
>in parallel? The LRM says (p 7-4)
> One or more module instances (identical copies of a module definition)
> can be specified in a single module instantiation statement.
>How does this differ from what we mean by multiplicity? Can one change
>a parameter value for just one of the instances through a defparam
>statement? If the ports/nets are buses, does one bit get assigned to
>each instance?
>
>
>-Geoffrey
>
>
Verilog does have instance multipliers, although it may only appear as
the "[range]" item in the instance
BNF in the newer LRMs ( I think generate is now the prefered mechanism).
Stu's quick ref . has it -

http://www.sutherland-hdl.com/on-line_ref_guide/vlog_ref_top.html
(instance_array_range)

- bsim5 #(...) mn1 [1:5] (...) would probably do the right thing.

Ask the BTF if you need clarification.

Kev.

-- 
Kevin Cameron, CPU Technology, CA 94588, Tel.: (925) 225 4862