Re: gEDA-user: A little puzzled about the purpose of gschem

[John Doty <jpd@xxxxxxxxx>]

On Apr 21, 2010, at 11:26 PM, Madhusudan Singh wrote:

> Basically, I need to painfully enter all the parameters for a 741 !

No, basically you need to find some manufacturer's model file. gEDA can't include those for legal reasons, but even the expensive commercial packages that include models only have a subset of what you need for a real design.

>   There is even a file parameter where I can presumably enter the
>   filename containing the spice model by hand.

Use that once you have a model file, yes.

Often I just use the model-name attribute to specify a subcircuit name and then include a file of subcircuits with the spice-include-1 symbol.

> 
>   At that point I stopped to take stock of the whole thing. Correct me if
>   I am wrong, but isn't the entire point of having a GUI entry to ease
>   and more importantly, speed, the development process ?

Fundamentally, the purpose of GUI is graphical communication. But for non-graphical processes, GUI gets in the way. It therefore scales poorly to big jobs: they turn into manual button-pushing exercises, when automation is needed. gEDA is a flexible toolkit that scales very well.

> So, precisely in
>   which way is using gschem more efficient than typing in a spice script
>   if I have to painfully pointy-and-clicky every damn single attribute
>   into this ?

It creates a drawing in a format that allows gnetlist to generate the connections from the graphics.

> Some might say that after defining a symbol, I can copy and
>   paste it to create more complicated circuits, but that is what a subckt
>   definition is for.

One thing gEDA lets you do easily is to build a library of custom symbol files that precisely match the needs of your projects and processes. And a lot of us share such files at gedasymbols.org.

> 
>   I guess I am asking - what purpose does gschem serve

It's good for schematic capture for just about any purpose at all. gnetlist can export a wide variety of printed circuit board netlists, SPICE, Verilog, bills of materials, and even Mathematica code for symbolic circuit analysis.

> (other than to
>   create pretty pictures, and being a humongous waste of time otherwise
>   since its basically asking you to enter the entire spice script, albeit
>   in disparate pretty boxes) ?

But it doesn't ask you to do that. Go back and read Stuart's whole document.

The power of gEDA? Well, last week a question came up about a mixed-signal VLSI design I put together using gEDA a couple of years ago. So I went to the simulation directory, typed "make PreamplifierTest". The Makefile rules figured out which subcircuit netlists needed to be generated, generated them with gnetlist, and then put me into ngspice with the simulation loaded. All I had to do was "tran" and "plot" to get the specific output I needed. No elaborate GUI procedures to reconstruct from memory, just three simple commands.

gEDA is a flexible kit of tools that plays well with other tools (make, tex, awk, layout tools, ...). That makes it good for a wide variety of jobs. For big jobs it's far more productive than the integrated point-and-click-all-day-long tools.

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




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