Re: gEDA: directives question

[sdb@xxxxxxxxxx (Stuart Brorson)]

Hi guys,

The use of a directive sounds interesting, but in the case of
attaching routing parameters to a net, I wonder how it
differs from just attaching an attribute.

IIRC, when doing high-speed stuff using the Viewdraw -> Allegro flow,
I just had to attach routing attributes to the nets in order to set
things like diffpair length tolerances and the like.  For example, I
just double clicked on the relevant net, and added DIFFPAIR=VIN to two 
different nets (VIN_P and VIN_N, say) to cause Allegro to know that
they were related to one another.  Then I added a rule like
DIFFPAIRLENGTHTOL=10 to those nets to cause Allegro to make their
lengths match to within 10 mil.

What does a directive do that is different from this?  Is there
something else a directive gives you, like the ability to switch it on
and off from the command line? 

Stuart


> 
> Hi Dan,
> yes, I think it can be used for that. gnetlist now builds two netlist:
> the traditional one and another netlist of objects with the attribute
> "graphical=3D1" set.
> I plan to have the nc symbol with attributes:
> device=3DDRC_Directive
> value=3DNoConnection
> this way the backend can check for the directives of a net, so routing
> style, differential pairs and so on can be added as well. You can look
> at the drc2 backend for an example.
> Of course, gsch2pcb and pcb have to support them if you want to use
> this.
> 
> Regards,
> 
> Carlos
> 
> El s=C3=A1b, 22-04-2006 a las 23:03 -0400, Dan McMahill escribi=C3=B3:
> > Hello,
> >=20
> > I noticed a commit message for adding 'directives' to gnetlist.  I=20
> > wonder if this mechanism could be used to specify routing style to use=20
> > for different nets when using the PCB autorouter.
> >=20
> > Or can one just add an attribute to a net to specify this?
> >=20
> > -Dan
> 
>