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Date:	Thu, 9 Jul 2015 16:38:24 +0200 (CEST)
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Subject:	Re: [geda-user] Back annotation (was: developer excitement?)
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On Thu, 9 Jul 2015, Roland Lutz wrote:

> On Thu, 9 Jul 2015, John Doty wrote:
>> If you?re just making changes until a diff shows nothing, it doesn?t matter 
>> whether you make them upstream or downstream. Just quit when you have a 
>> match!
>
> This sounds reasonable to me.  So the common denominator is to load a "target 
> netlist" into gschem and show the differences between the current state and 
> the target state, either by highlighting them in the schematic or by showing a 
> diff?  This shouldn't be too difficult to implement.

On gschem's side, I think so.

Although things could get a little more tricky with multipage schematics, 
hierarchical schematics, buses, and so on.

>
>> nearly all of the unnamed nets changed their names in this case
>
> A clever diff algorithm would have to compare connectivities independently of 
> net names, so the remaining net name changes could easily be ignored.

Good point about nets.

A separate issue is attributes; replacing the footprint during 
layout (common in my practice) is actually a change in the attribute in 
gschem. For the first glance, as an user, I'd be happier if it went 
automatically, but I have corner cases where it could break slightly or 
terribly. Example for the latter is my special gsch2pcb variant for 
breadboards; there I can have multiple footprint attributes (with 
different attribute names) and my gnetlist variant decides which one to 
use (tru-hole for breadboard modelling and smd for the final board). If I 
wanted to back annotate a footprint change automatically, the back 
annotation script would need to understand this mechanism. This suggests 
the obvious: back annotation glue scripts should be external and easy to 
replace. We can avoid language-lock-in with John's idea I also support: 
design a good and well documented netlist/attribute-changes language for 
back annotation, so anyone can code their own scripts in whatever language 
they prefer.

An alternative to tricky back annotation scripts: if attribute changes 
don't happen automatically, nothing gets messed up (but the user has to 
spend more time manually changing things on the sch). Maybe this could be 
a setting somewhere.

Regards,

Igor2

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