Re: gEDA: Dumb (g)netlist question.

["Richard G. Munden" <munden-at-NOSPAMacuson_dot_com>]

Ales,

Power (and ground) symbols can be thought of (or implemented as)
hierarchical objects.  They do not represent physical components.  The
purpose of a power symbol is (or should be) to connect a wire to a power
net.  This is an aliasing function.  The result should be that +5V and
NETNAME become the same.  The tricky part is determining which name
shows up in the netlist.  You could wind up having *all* your +5V net
renamed to NETNAME which should make no difference to the next tool but
might befuddle the poor user.

Rick


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
> 
> START nets
> 
> +5V : U100 1, U100 14
> GND : U100 7
> NETNAME : U100 1
> 
> END nets
> 
>         As you can see, the +5V net consists of U100 14 (the power pin on
> a hex inverter) and the +5V connection caused by the VCC symbol/net.
> And you can also see the NETNAME net which just consists of U100 1.  The
> above output doesn't equate +5V to NETNAME otherwise it would say:
> 
> NETNAME: U100 1 U100 14
> 
> 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