Re: gEDA-user: "Now who's with me?"

[John Griessen <john@xxxxxxxxxxxxxx>]

DJ Delorie wrote:

>>  -- putting out a new version of the
>> gnetlist-pcb netlist with circuit values for the trace capacitances
>> and distances.
> 
> The LF netlister is all new anyway, I could add more attributes if
> needed. 

[jg]    I read here: http://www.linuxfund.org/projects/pcb/proposal/
that the LF netlister means forward annotation.

  The thing is, PCB doesn't do anything with them at the
> moment.  How would gschem know about trace capacitances anyway?  The
> netlister is only sch->pcb at the moment.

[jg]I wasn't thinking of the gschem representation of the design getting back annotated,
just a separate simulation version of the design schematic.  A subset that is the zone of interest for simulation purposes.
Hmmm... back annotation -- I guess a good way would be similar to the way PCB handles
an imported netlist -- it shows rat-nest lines and notes how many missing nets there are.
That kind of functionality in gschem would be handy for adding trace capacitance lumped parameter
components to a simulation schematic.  You would not want all of the netlist usually, just the part
you are simulating, so having a way to export only some from pcb would be a good way.  Drawing a polygon on a layer
so it contains the traces you want exported for back annotation is what I think of first for selecting a zone of interest for 
simulating.  Then the back annotation file could be a difference file -- a to do list of changes to make just like the .pfa 
forward annotation file in the LF proposal.

I guess my idea doesn't fit in the LF proposal after all -- it would mostly be an addition to gschem rather.  To add gschem
functions that let you load a netlist, then add components to match it as in pcb layout.

Instead of that, you could just handle little cases like trace capacitance as a special feature of wires, but that
would be specific and a fair amount of work.    To import new netlist elements would be general and more power/flexibility.

So the short answer is:  gschem would know about trace capacitances by getting a "match the netlist" mode
as well as the "extract the netlist from the current state of the schematic" mode it has now.

John Griessen
-- 
Ecosensory   Austin TX


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