At 11:15 AM 6/10/2002 -0700, Joey Nelson wrote:
>The online help for matched net length rules seems to imply that if I set 
>a rule for a set of nets and then run Tools->Equalize Net Lengths, that 
>the shorter net will be accordioned to make up the difference, space 
>allowing.  But this does not seem to be the case.  I've checked and the 
>tracks are not locked, and there does seem to be sufficient space, but 
>whenever I run Equalize Net Lengths, I simply get a design rule error.
>
>Is there some trick to getting this to work?  It certainly seems like 
>something the router should do, and I should not have to do by hand.

The tool does not use the router. It will look for space to accordion a 
track according to the rules set. I can't tell what is wrong with Mr. 
Nelson's setup, but I can encourage him by noting that the tool *does* 
work, I've used it a number of times.

The most likely cause of failure is insufficient space to add the meanders. 
They take more space than one might expect.... The meanders are added, if I 
am correct, one net at a time, so a set of parallel nets will *not* meander 
together; rather, one will be meandered and very possibly the second will 
not have room. But Mr. Nelson seems to be reporting that no meanders at all 
are created.

One would normally setup a Net Class to which the nets to be equalized are 
assigned. The Match Lengths rule defines the parameters for the meander as 
well as the acceptable variation in length. If the tool cannot create 
meanders sufficient to bring the nets into compliance, yes, a DRC error is 
created.

But I recommend experimenting with a very simple PCB with two nets. If you 
can get it to work there, you may then be able to get it to work on a more 
complex board.

Someone else, of course, may have more experience with the tool than I.... 
I did, sometimes, create the meanders myself, relying on the Design Rule 
only for verification of net length match.


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