Hi Stuart, Maybe there is no difference between directives and attributes. The main goal of the directives was to add a graphical object to a net, so the backends could change their behaviour (i.e: the no-connect symbol). It is like an attribute, but attached with a graphical object.
I suppose the backends can also look for a net attribute, but in the case of the nc symbol there was no way to add an attribute to a net using a symbol. Regards, Carlos El dom, 23-04-2006 a las 17:28 -0400, Stuart Brorson escribió: > 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 > > > > >
