Re: gEDA-user: Toporouter Changes

[Ethan Swint <eswint.ramu@xxxxxxxxxxx>]

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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