gEDA-user: Some thoughts about PCB track attrs in your schematic [was: Re: autorouter fixes and enhancements]

[Christoph Lechner <cl0023@xxxxxxx>]

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Dave McGuire wrote:
> On Jun 22, 2009, at 1:33 PM, Stefan Salewski wrote:
>>> A bunch of fixes and enhancements to the original pcb autorouter
>>>    should now be available in the git repository.
>> I wonder if the PCB autorouter should be more closely bound to the
>> gschem schematics. For example, in the schematics we may specify
>> priority of nets (fast signals, power, ...), trace width or clearance
>> for net segments. Maybe by attributes? I have no idea how  
>> commercial EDA
>> software handles this.
> 
>    I don't know how commercial EDA software handles this either, but  
> regardless of what they do, this functionality sounds extremely  
> powerful.
5 years or so ago, I had to work with Protel98. The solution there was
to add a special symbol (a red crosshair, if I'm right) to the net in
question and then specify PCB properties like track width in the schematic.

But I believe that would be possible to realize even with the current
versions of the tools (gschem, gnetlist, gsch2pcb, pcb).
In gschem one would add a new component to the library with one pin that
has to be attached to the net we want to have special properties. In the
value attribute one would say "width=50mil".
IMHO the best way is to add another script to the toolchain.

So:

           gnetlist                    (*)
gschem -->   *or*   --> "the new tool" --> import into pcb
           gsch2pcb          |                  ^
                             +------------------+
                              (import attributes of nets
                               via ExecuteFile)

The new tool would then create a script of actions to run using
ExecuteFile in PCB. OTOH the special component has to be filtered out
from the stuff fed into PCB, so it appears if there were no instances of
that component. Then after importing the filtered gnetlist output into
PCB (the (*) arrow), one executes the script generated by the filter
program and so the track width attributes of the nets are set to the
proper value.
Because the component was attached in the schematic fed into gnetlist we
know which net to set the track width.


CU
- - cl
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