Re: gEDA: Dumb (g)netlist question.

[Matt Mozur <matt_dot_mozur-at-NOSPAMflashcom_dot_net>]

Ales Hvezda wrote:
> 
> Hi All,
> 
>         This may be a really dumb question, but here it is anyways. :-)
> 
>         Suppose you have a circuit which looks like this:
> 
> v 19990829
> C 17900 22900 1 0 0 7404-1.sym
> {
> T 17800 23800 5 10 1 1 0
> uref=U100
> }
> N 17400 23400 17400 24500 4
> {
> T 17500 24100 5 10 1 1 0
> label=NETNAME
> }
> C 17200 24500 1 0 0 vcc-1.sym
> N 17400 23400 17900 23400 4
> 
>         Here's a textual description:
> 
>                 You place an inverter gate and the symbol for VCC on a
>                 schematic sheet.  You connect one of the pins (input)
>                 of the hex inverter to say the VCC symbol.  You are
>                 connecting Vcc (or whatever) to the input of the
>                 inverter gate.
> 
>                 So far that's a valid thing to do.  Maybe a bit odd, but
>                 valid never the less.  Then you:
> 
>                 You label the connection between Vcc and the input pin
>                 as NETNAME. (using the label= attribute)
> 
>         I've been working on the power/gnd mechanism in gnetlist (the net=
>         attribute) and when you do the above you are in fact creating
>         a net called +5V (this net is defined in the VCC symbol as:
>         net=+5V:1) and connecting it to the input pin of the hex inverter.
>         So far so good.
> 
>         However you have also named that particular net NETNAME.
>         So, you have effectively equated NETNAME to the +5V net.
>         How should this be handled?  Right now here's the gnetlist output
>         for the above schematic:
> 
> START components
> 
> U100 device=7404
> 
> END components
> 
Well, how about assigning one of two classes to a net: either
LOCAL or GLOBAL?  A GLOBAL net would generally be used for
power and ground connections - and, a GLOBAL net name will
override a LOCAL net name (as far as the netlister is
concerned).

The user could apply his LOCAL net name, and when viewing the
schematic
it shows him his net name.  The only issue is that the netlister
should
warn the user that a LOCAL label is being replaced with a GLOABL
label.

This is similar to the Viewlogic scheme...


mm


> The the grand question really is:
> 
>         So how should gnetlist handle the assigning of net names to nets
>         which are explicity assigned and those which are created by the
>         net= attribute?  (Assuming you connect these nets together).
>         Or another way to look at it is assigning two different net
>         names to the same net.  Should this be allowed?
> 
>         Blah, I have no idea if that made any sense; I've been coding for
> 5 hours straight now and my mind has gone to total mush.
> 
>                                                                 -Ales

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