Re: gEDA-user: A couple o' questions

[Carlos Nieves Ónega <cnieves.mail@xxxxxxxxx>]

El jue, 06-04-2006 a las 17:44 -0600, John Doty escribiÃ:
[snip]
> > It is ok right now. A passive pin can be a power source (through a
> > diode, resistor, or whatever), so DRC won't complain about it.
> 
> OK, so you won't demand that pwr_in actually be connected to a  
> recognizable power source. But there's a whole common class of  
> blunders you thus cannot detect. Furthermore, it's actually one of  
> the few places where DRC might catch a problem that's difficult to  
> spot otherwise: passive power.

As you said, the DRC has to do automated checking, don't give false
errors, and can't substitute the designer's mind. So it isn't possible
to automate it that way without giving a _lot_ of problems. It's
perfectly right if I give all the power to a circuit through a
connector, which should have passive pins. There is no tool which can
figure out where it is going to be connected there. I'm not wondering
about things impossible to detect, but common errors which can be easily
detected, reported and avoided.

[snip]
> A 7805 regulates the output to be 5V above the GND pin (if it can). A  
> whiff of current flows from IN to GND, but in most applications most  
> current flows from IN to OUT, so it's more sensible to think of GND  
> as a reference potential input than as power. I have a 6/12 volt  
> battery charger that regulates with a 7805 using an adjustable  
> voltage divider between OUT and system ground as input to GND: this  
> sets the output voltage to 7.2V or 14.4V, depending on the battery.

If a pin is an input, the current flows from outside to inside the IC
through that pin. Usually in a 7805 the current flows out of the GND pin
(from the 7805 to your circuit), so I would say it is a pwr_out. At
least can we agree it is a pwr pin...

> The point here is that you and I can probably thrash out what pintype  
> to use, and understand the consequences. But is isn't a simple  
> problem to figure out, and outside the digital word such ambiguities  
> abound. That's no doubt part of the reason for the lack of pintypes  
> on many gEDA library parts.

There can be some difficult cases, but not all. All passives hadn't the
pintype attribute, and it is obvious what it is. The only ones I left
when I was adding the attribute were the ICs, mainly because for most of
them I'd have to download the datasheet and see what they were. It is a
tedious work now, but it is not so much work when someone is creating
the symbol.
The main reason for the lack of pintypes is that people didn't care when
the symbol was created.

[snip]
> But the program won't find the tough things, at least in analog: it  
> only finds trivia. 

As I said, I left those trivial problems to the DRC, thus having more
time to find non-trivial problems.

> Worse, getting it to shut up about non-problems is  
> a distraction: your time's better spent looking for the real  
> problems. Of course you can disable checks, but that reduces whatever  
> positive value it has.

I usually don't disable any check: I define the pintypes and run the
DRC. It doesn't give so many false errors.

[snip]
> We've been discussing the 7805. The lm7805-1 symbol has no pintypes.  
> None of the symbols used in the attached example has pintypes. Note  
> that I'm using 20050820: there are apparently no Fink packages for  
> the current release, but is the current release better? I'm thinking  
> of going back to a tarball install on my Mac.

Yes, please. There was a lot of attribute work committed to CVS in
09-12-2005 (european date format: DD/MM/YYYY). 
Just now I have commited some changes to the asic/ symbols, adding some
missing pinlabel and pintype (passive) attributes, so maybe you can use
the symbols in CVS.
You are right: the 780x don't have pintypes. All the linear directory
are ICs, and as I said earlier, I only fixed some of them. I expected
that people fix the symbols as soon as they were used... I was rather
optimistic...

> >
> > [snip]
> >> 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.
[snip]
> Here it is, a real example with only the corporate graphics missing:

Thanks for posting it!. I reviewed it, run the DRC, and got some errors.
All of them were related to missing pintypes. I fixed the symbols in the
asic library (added the pinlabel and pintype attributes), and tried
again: the result was no errors neither warnings.
I'd want to try some other schematics with false errors you were talking
about, so if you have more by hand, please post!.

Thanks,

Carlos