Re: gEDA-user: Resistor values…

[John Doty <jpd@xxxxxxxxx>]

On Dec 25, 2010, at 11:51 AM, Vanessa Ezekowitz wrote:

> On Sat, 25 Dec 2010 07:33:30 -0500
> John Doty <jpd@xxxxxxxxx> wrote:
> 
>> 
>> On Dec 25, 2010, at 1:50 AM, Vanessa Ezekowitz wrote:
>>> 
>>> Resistors are just one of many component types out there have a value, no
>>> matter what type of package they come in
>> 
>> Resistors often don't come in packages.
> 
> "Often", perhaps, but not usually.  No matter how you slice it, the most common way to use such a symbol and its corresponding physical representation is as a component on a circuit board or in an IC.

Maybe for you. But gEDA isn't limited to that kind of flow. I pray that it will remain flexible, not specific to any particular kind of flow.
 
> 
>> I use resistors in VLSI design, and
>> textbook symbolic abstractions of resistors also have no packages. Then
>> there's simulation, where it is usually unnecessary to simulate the package
>> even if it will exist someday.
> 
> Stop trying to change the subject - this is not about simulation or VLSI design,

Yes it is. It is extremely important that gEDA remain the excellent tool for these jobs that it is.

> or even the package types that such resistors come in - it is about the sheer fact that resistors *must have some kind of value* when they are finally put into physical form.  If they do not, they are not a resistor, they are a conductor.
> 
> If the presence of a "value=" attribute is of no use to you, then *ignore it*.  

If the absence of a value= attribute is a problem for you, attach one. Even if it's present, it's likely to be wrong, so you have about the same amount of work to do in any case. But getting rid of it is somewhat more work, especially in existing schematics that assume its absence.

> 
> The existence of something does not imply the requirement to use it.
> 
>> gschem/gnetlist are excellent tools for
>> schematic capture for VLSI, symbolic analysis, and simulation.
> 
> And they will continue to be.

They won't if the attitude of "I don't care to know about any flow except pcb, and all I want is my version of the pcb flow" isn't vigorously opposed.

>  The proposed change won't affect the subset of people who use them for those purposes.
> 
>> By convention, in symbolic analysis of circuits, the value is the same as
>> the refdes. So no value attribute is needed.
> 
> Maybe in your line of work that can be the case, but I submit that the vast majority of users of these types of tools do not make the same comparisons you do.

Ah yes, the tyranny of the majority. But I'm here because gEDA is far more flexible and productive than the competition. I guess all the other gnetlist back end writers contributed for the same reason.

>  
> 
> You and I both know that "R1" is not meant to have the same meaning as the "10k" written below it in a schematic, and that's what each of our respective instructors taught.  

Ah, but in pure symbolic analysis there is no "10k". There are only equations like "r1*c1==4*r2*c2".

> 
> Please don't try to push the rest of the world away from this fact.  They are two parameters with two completely different meanings.
> 
> Of course, I was taught at a time when EDA tools were non-existent for the end-user, so simulation was something you did with pencil and paper, schematics were passed around in printed form or as plain hand-drawn image files, and circuit boards were drawn, etched and stuffed by hand if you wanted something better than breadboard or wire-wrap.  I'm sure that has a lot to do with my perception.

I started with vacuum tubes and point-to-point wiring. You can't go from there to VLSI without changing a lot of thinking.

> 
>>> The same goes for every last capacitor, inductor, etc., though I think
>>> you'd be hard-pressed to find any that have a value of zero.  
>> 
>> Maybe you're hard-pressed here, but I am not. I often set values to zero
>> when analyzing or simulating circuits. Limiting cases, y'know. Sometimes I
>> even use negative numbers.
> 
> Fine, so continue to do so.  No one is stopping you.
> 
>> If you only use gschem/gnetlist to feed pcb, you will have a severely
>> limited perception of their true capabilities, and the genius behind their
>> design.
> 
> Perhaps you mean "you will have a somewhat narrow need for their true capabilities".

No, the limited perception is a problem. You propose a change that will break a significant subset of my library of schematics because you don't see the breadth of gEDA's utility.

> 
> The same could be said for a text editor, if all I ever do with one is work on the HTML for my website rather than write the Great American Novel.

A nice simple text editor is a good thing. Versatile. A WYSIWYG word processor is much less versatile.

> 
>> It would be great if pcb users would pool their resources and create a
>> library specifically for a common pcb flow. But it will never happen. Even
>> in that small corner of the vast gEDA universe there are still widely
>> divergent notions of flow and style. So almost everybody will continue to
>> fight the toolkit and complain.
> 
> About the only one fighting this proposed change is you, John.

Ah, the tyranny of the majority again.

>  All we are proposing here is adding some reasonable, sane defaults for things like "value" - things you can ignore if they aren't useful to your particular work.

If you add a value= attribute to resistor-1.sym it will break most of my symbolic analysis schematics because of the inheritance rules. The presence of specific values overrides the default of "use the refdes symbolically".

Again, the right answer is not to change the default library, but to create libraries for specific purposes on gedasymbols. If you really must have a symbol with different semantics in the default library, the convention is to give it a new number. But you're not going to fix the underlying problem that the default library is a grab bag by any means except the creation of specialized libraries for specific flows.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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