[SI-LIST] Re: Developing High Speed Routing Rules

Hello Wilbur:

I certainly don't want to take business from the SI consultants out there, as 
there are some pretty good ones, and I wouldn't be surprised if some of them 
have already e-mailed you.

To me, though, it's not really an either/or decision.  Each approach offers a 
different set of benefits, and both approaches have upfront costs, and 
"lifecycle" costs.  So, your decision might be more easily resolved if you 
factor in the time horizon that you're wanting to optimize across (e.g., one 
project vs. the next 18+ months), as well as how you weight educational benefit 
vs. a quick-fix to your current design problems.

With a consulting model, you're learning and getting design help while they're 
on the clock.  With software, the "consulting" is you and the tool working 
together, and you can consider having an actual consultant come in for the more 
difficult problems.

SI Software and Routing Rules:
I don't think that most in the SI software world would agree with the statement 
that the software just helps you develop routing rules.  I can think of 100 
other things that a good SI software package can do beyond creating canned 
design rules to feed to a router.  Every rule has a whole list of assumptions 
built into it, and you can end up remembering and applying the rule, but 
forgetting all the assumptions.  Moreover, when one variable on the assumption 
list changes, the rule itself may be out the window.

As an example, I tell my 4 year old son not to play in the street.  (He's a 
wild man.)  That's kind of like a routing rule.  When he gets older, maybe 8 or 
9, I won't give him that routing rule because he'll know enough to listen and 
watch for cars, navigating around them.  In this analogy, the consultant would 
be like the parent saying, "I'm not going to be around all the time, so -- 
while I'm gone -- always route it this way."  As a result, you may experiment 
less, learn less, and end up overconstraining your designs, or adding 
additional product costs through layer count, board space, overkill on passive 
components, etc.

In my son's case, rules are a surrogate for me (the "consultant") being there 
until he knows what to do.  In your case, I'm not saying it's an either/or 
situation, but you may find that a good simulator accelerates the rate at which 
the delta between what you and the consultant know is smaller and smaller.  
(E.g., Instead of using a 3H separation rule for crosstalk, you can try 1.5H, 
potentially saving board space, and comparing the results to your target 
thresholds for the technology you're using.)  

Would you like to know which simulator I recommend? :-)

Bill Hargin
Mentor Graphics Corp.
Systems Design Division
High-Speed Tools
425-497-5079 - Direct
425-246-9937 - Mobile

> -----Original Message-----
> From: Harvey, Wilbur [mailto:Wilbur.Harvey@xxxxxxxxxxxxxx]
> Sent: Tuesday, June 17, 2003 1:02 PM
> To: si-list@xxxxxxxxxxxxx
> Cc: Yao, Jimmy; Au, Gabriel; Yuen, Patrick
> Subject: [SI-LIST] Developing High Speed Routing Rules
> 
> 
> We are trying to make the tradeoff of purchasing tools such 
> as HyperLynx or
> Specctraquest.
> 
> The most important use of these tools that we see, is to develop the
> Specctra routing rules.
> 
> Specifically we are working in the domain of 600Mhz LVDS and 
> Rocket I/O, as
> well as the normal STTLII for the DDR memory interfaces.
> 
> The question is, over a several year period, would we be 
> better off to hire
> outside companies to develop these rules for us as needed, or 
> to have the
> tools in house and develop them ourselves. Any comments would be
> appreciated.
> 
> If anyone has any leads on who we could contact to get prices 
> on developing
> these rules it would be appreciated as well.
> 
> Wilbur Harvey - Engineer
> Spirent Communications Inc., www.adtech-inc.com
> First Hawaiian Center, 999 Bishop St.. Suite 1700
> Honolulu, HI 96813
> Tel: +1 (808) 440 3494, +1 (808) 440 3363 (Direct)
> Mobile: +1 (808) 221 0395
> email: wilbur.harvey@xxxxxxxxxxxxxx
> 
> 
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