[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: gEDA-user: A couple o' questions
Just remember that all the DRC checks are configurable and can be
disable. If anyone doesn't want to do it, then disable it. If you are
doing analog design, then you can disable the pintype checking, since it
is the one you are always having troubles with.
El miÃ, 05-04-2006 a las 14:11 -0600, John Doty escribiÃ:
> On Apr 5, 2006, at 1:31 PM, Carlos Nieves Ãnega wrote:
>
> > Current pintype attributes are defined in the same way as commercial
> > packages I've seen. What I also miss is the "power source" or "power
> > sink" pintype. Adding them to the DRC is fairly trivial, and also
> > to the
> > docs. Would it be better to have pwr_in and pwr_out pintypes?
>
> Consider linear/lm7805-1.sym. No pintypes. But what should they be?
> Well, maybe OUT should have type pwr_out (if it exists). But what
> about IN? Perhaps pwr_in seems sensible, but then it's most likely
> connected to a diode and a cap: will DRC be able to figure this out?
diode and capacitor are passive..
passive connected to power are ok for the DRC. In fact, passive
connected to whatever is ok.
> Then there's GND, what pintype is that? Remember that it's perfectly
> sensible to connect this to something other than ground, to get 5V
> *relative* to some other potential.
GND is pwr. If you are defining an IC which needs to be powered, and VCC
is pwr_in, let me assume for a moment that GND is pwr_in.
In a circuit you will have a lot of pwr_in (your IC's), and maybe a
power connector or a power source for simulation. The first won't raise
an error (the connector is passive and it can be connected to a power
pin), but I see some tricky scenarios in the latter:
- two voltage sources in series: pwr_out connected to pwr_out.
- two current sources in parallel: pwr_out connected to pwr_out.
These are special situations where the DRC will normally report an
error.
If the DRC directive is going to be supported, what I'd do is to place a
DRC directive "Not do pintype checking in this net". This way I'm
telling gnetlist: "Hey, I'm aware of this one. But tell me if you find
another one!". That's the difference between disabling that check
forever, or just for that net you are aware of. What if you have another
one you haven't noticed?
The DRC only will complain if you connect a pwr pintype to:
- unknown pintype: it doesn't know what to do. This situation
shouldn't happen if the symbols are well defined.
- out pintype: you will short the output to a power rail.
This can be ok if you are connecting an output to a pwr_in pin: you
are supplying power through an output pin.
- io pintype: it raises a warning, because the DRC doesn't know what
you are doing. Is it an input, and output, both?
- oc, oe, tp, tri, clk: they are outputs. This connection can be OK if
connecting to a pwr_in pintype (maybe for clk and tp, but not so sure
about oc,oe: error? and tri: warning?).
FMPOV the combination of the pwr_in and pwr_out pintypes, together with
the DRC directives will drop the failing situations to a minimum, and
can be controlled by the user. The DRC is there to help you, if you
want. Yes, it needs some extra work, is it worth?. If you don't want it,
then disable it or don't use it.
> The trouble I see is that the correct pintype needs to be obvious to
> the symbol creator, or chaos results. In pure digital stuff the
> correct pintype usually *is* obvious, but in other applications it's
> not.
I agree absolutely. Getting the correct pintypes is tricky in analog.
what is needed to improve this situation? I guess if we have pwr_in and
pwr_out it would be easier (I don't mean fail-proof).
I have one more question: what checks should your analog designs pass?
The only complaint I see regarding DRC in analog desigs is the pintype
checking. Are the other checks enough?, are you doing some more checks
not considered in the DRC?
Regards,
Carlos