Re: gEDA-user: A couple o' questions

[John Doty <jpd@xxxxxxxxxxxxx>]

On Apr 5, 2006, at 4:33 PM, David Logan wrote:

> One thing I would recommend is "harshest or most on by default, let  
> the user back it off." In other words, I think DRC should check  
> everything but everything, and let the user know how to lower those.
>
> In general, if you do it the other way, you get users that are  
> happy about passing when its really not. It's much better to fail  
> for valid reasons than pass for invalid reasons.
>
> And the main point is this: We all know how general behavior goes.  
> If a users DRC is failed, and he/she/it wants it to pass, they will  
> ask/read/learn. On the other hand, if DRC happily passes due to  
> disabled checks, he/she/it won't take the time to make sure that  
> his passing grade is actually valid.

It isn't a matter of grading: it's a matter of getting a job done.  
Strictness based in error is counterproductive. If DRC was  
*reasonably* accurate what you say might make sense, but:

Many components in the libraries don't have pintype attributes, and  
it isn't even obvious how to fix them.

DRC screams about too many non problems. It doesn't understand  
hierarchy, at least the way spice-sdb does. It thinks unconnected  
pins and single pin nets are errors. A simple error-free CMOS  
inverter SPICE subcircuit made with library MOSFET symbols gives 8  
DRC errors for only two components, correctly connected. It isn't  
worth trying to figure out how to fix these when for the stuff I do  
DRC can't find the really important blunders anyway.

I suspect that in a pure digital design organized the way Carlos does  
it, DRC is very useful (but that isn't the kind of work I do). For my  
sorts of designs it "strains out gnats and swallows camels", and it's  
difficult to see how to make this sort of formal logical process  
work, when the issues are really in the applied physics domain. An  
exercise in AI...

So, how's a newbie drawing an analog circuit to know *which* errors  
to pay attention to? Chasing them *all* down is a waste of time.

The fable of "The Boy Who Cried Wolf" applies here.

Please note that I am *not* complaining about Carlos' valuable  
contribution here. What I object to is the idea that DRC is  
*universally* useful. It depends on your design flow and application,  
and I don't think trying to make it universally useful is even a  
sensible goal. Different applications need different flow, different  
tools. What's really nice about gEDA is that you can mix and match.  
You don't need to use DRC if it isn't helping, but you have it for  
when it *does* help. Just have to be sensible about drawing that  
distinction.

> David Logan
>
> > It makes complete sense to you: it's your thing. It makes a great   
> > deal of sense to me too. But for a newbie, I think it just makes  
> > the  job of getting a simple result more difficult. DRC is a power  
> > tool  for experts doing big jobs (especially digital), not  
> > something of use  for the simple but subtle projects newbies tend  
> > to start with.

John Doty              Noqsi Aerospace, Ltd.
jpd@xxxxxxxxxxxxx