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Re: gEDA-user: Toporouter Changes
On 07/07/2009 08:21 AM, Peter TB Brett wrote:
> On Tue, 07 Jul 2009 07:16:04 -0500, Bill Gatliff<bgat@xxxxxxxxxxxxxxx>
> wrote:
>
>> Anthony Blake wrote:
>>
>>> I would prefer to implement this sort of functionality with topological
>>> directives or constraints, and avoid geometric constraints if possible.
>>>
>>>
>> Kind of like providing the circuit-board equivalent of a geological
>> topographical/relief map, so the algorithms know where the "valleys"
>> (preferred paths) and "peaks" (mountains, don't climb them unless
>> necessary) are? And the lakes, airports, Area 51's, etc.... Except
>> that with circuit boards it would be more than 3-D, because some of the
>> mountains would be abstract things like excessive trace length (which
>> might later trigger the addition of a via and then a retry), DRC rules,
>> desire to avoid the extreme edges of the board, and so on... An [n]-D
>> "relief map"...
>>
> Yes, you've just described geometric constraints in great detail. :P As I
> understand it, topological constraints are something completely different!
>
>
A little late to the discussion, but here's my $0.02: topological router
is the only practical way of finding prospective routes between two
points, but the geometric constraints are what really matter (provided a
path is found!) to the performance of the circuit.
So once a topological solution is provided, optimizing artificial
potential or cost functions based on geometric and electromagnetic
criteria would be the best way to route within a Voronoi cell, possibly
with an edge from the corresponding Delaunay diagram as a starting
candidate. (It looks like this may be the way it's done already?) If
multiple paths are found, the 'best' path would be chosen by evaluating
the cost functions.
Moreover - the cost multiples could be assigned to each branch of a net
(or groups of branches), e.g. the distance from a USB connector to the
receiver chip would be very high, the difference in the distance between
a parallel interface is high, the area between two differential traces,
etc. This would provide a *lot* of smarts to the autorouter, and maybe
expanded to an auto-place routine, as well.
Anthony - the router is looking fantastic!
-Ethan
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