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From:	Kai-Martin Knaak <knaak AT iqo DOT uni-hannover DOT de>
Subject:	Re: [geda-user] Antifork
Date:	Wed, 26 Aug 2015 22:43:40 +0200
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Evan Foss (evanfoss AT gmail DOT com) [via geda-
user AT delorie DOT com] wrote:

>> My fantasy when I heard about ruby scripting in pcb was that perhaps
>> Stefan's router might someday see the light of day afterall.  Oh well
> 
> I keep seeing mentions of this legendary router. I have been these
> gEDA lists +10 years but I don't remember it. What was the big appeal
> if it?

It comes up with cool looking layouts. When done properly, the technology 
promises to be very efficient and find clever solutions. There is a little 
demo on youtube from back in 2012 when the toporouter sort of worked:
	https://www.youtube.com/watch?v=NqT4ZYGB3VY

As fancy as the result looks, the toporouter never lived up to its 
potential. The state shown off in the video has several significant 
limitations.

* The algorithm is all-or-nothing by design. It can only applied to the 
whole layout. You cannot tell it to route just this subset of connections. 

* The algorithm restricts it self strictly on one side of the board for 
any given net. That is, when in a dead end, it is not able to insert a via 
and switch to bottom and work from there. With thru hole components this 
is often less problematic. But SMD without vias tends to be unroutable.

* The router ignored any pre-routed copper, too. You had to start it on a 
footprints-only layout.

* As seen in the video, more often than not, there are a few unrouted 
nets. Typically these are hard to fix manually.

The developer who did the toporouter left the project when the Google 
summer of code he was financed by was over. Unfortunately, there was 
insufficient documentation. And the code style was such that the router 
was assessed as working but impenetrable by those who took a closer look 
after the fact. Even more unfortunately, there was a major shift at the 
core of pcb going on about this time -- the internal precision of geometry 
was pushed from 1/1000 mil to 1 nm. Ever since this move, the toporouts 
straight out fails.

---<)kaimartin(>---
-- 
Kai-Martin Knaak                                  tel: +49-511-762-2895
Universität Hannover, Inst. für Quantenoptik      fax: +49-511-762-2211	
Welfengarten 1, 30167 Hannover           http://www.iqo.uni-hannover.de
GPG key:    http://pgp.mit.edu:11371/pks/lookup?search=Knaak+kmk&op=get

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