"I think we need to define a base set of elements and properties for our first effort."
I disagree. I suggest that we first agree on the scope of the specification. Once that is agreed on, the elements required will follow. We need to know what the spec will be used for before we design the engine and chassis.
Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC Todd Westerhoff wrote:
Arpad, I understand what you're getting at, but I think you haven't acknowledged the other side of the problem: define a language that's so flexible and capable it can describe anything, and there's a chance no one will want to use it. We've already had that experience too; it's part of how we got here. I'm a big fan of keeping things simple - to me that means taking time up front to define the problem clearly and quantifiably, then considering potential alternative solutions ... at which point I tend to favor approaches that are simple and flexible. It's not that I don't believe in designing for future growth and expansion - it's just that I think designing a solution for a problem that hasn't been described yet is a trap. Such a project is plagued by questions like "well, what if ...", but it's almost impossible to describe the likelihood that such a situation will actually occur. At that point, it's not engineering anymore - it's conjectureering. SPICE is a good example of something that was designed to solve a particular problem, with a syntax that was simple and flexible enough to allow expansion. Of course, one SPICE became many SPICEs, became countless SPICEs, which is also part of how we got here. Walter's EMD proposal, in part, is intended to give us a common SPICE-like syntax we can all point to. If we have a language that allows us to describe connectivity and hierarchy in a standard way, then (I think) it's just a matter of choosing the right building blocks and properties. Adding new building blocks or properties as needs arise shouldn't be a spec-killer. The original IBIS approach (table & template-based, with no general purpose interconnect description) was designed to solve a very specific problem, and it solved that problem reasonably well. S2IBIS2 was also a step in the right direction, because it helped vendors create models, although many vendors lacked the resources they needed to develop and distribute good models. Where IBIS could have done better was adaptation. The template-based approach for the push-pull buffer was a good one, but we all would have been better served if there was a general purpose interconnect language to go with it, instead of having of having to amend the core spec for new requirements as they came along. We now have a language with lots of syntax, but too few tools and developers with enough knowledge to effectively deploy what we have. The template approach also contributed to the delay in supporting new features for the customer - first the language had to be amended, then the tools had to be updated. That tended to be a pretty long cycle, and hard to take in the face of accelerating design schedules. I don't see that we're headed down that path again, or I would have said so. I think we need to define a base set of elements and properties for our first effort. Getting a first spec together involves a simple tradeoff - the more building blocks and properties you want, the longer definition and debate takes. How soon do you want a usable spec? ... which brings me back to point 1. We need to spend more time defining the bounds of the problem we're trying to solve.Todd.Todd Westerhoff VP, Software Products SiSoft 6 Clock Tower Place, Suite 250 Maynard, MA 01754 (978) 461-0449 x24 twesterh@xxxxxxxxxx www.sisoft.com -----Original Message----- From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad Sent: Friday, June 27, 2008 3:39 AM To: IBIS-ATM Subject: [ibis-macro] Re: Question on seeting the EMD direction Todd, Good question regarding what I was getting at with my last point. I will try to summarize it briefly. Having had the "IBIS experience" multiple times over (criticism that IBIS is not as accurate as SPICE, ICM can't do this and that, etc...) I would think twice before I wrote a new spec to avoid a similar experience later again, so I tend to ask myself more general questions about what makes our specs so useless in some people's minds? The fundamental problem I see in most of our IBIS and related specs is that the modeling language they describe have "built-in" limitations (intentional or unintentional) and a lot of hard coded stuff. While I agree that not all models we write have to be valid all the way out to 1000's of THz and include all non-linear and time variant effects, I think the choice should be up to the model maker, and not a limitation of the language. Don't forget, we are trying to write a language specification here, not the models... A modeling language always has to be more capable and flexible than the models people want to write with it at any given time. Or as a minimum, the language has to be extensible so that at any given time more capabilities could be added to it. However, we are already talking about fundamental limitations, such as assuming that this language will be used for interconnects ONLY, everything is LTI, element values are constants (during the simulation) which may be hard to remove at a later time if there was a need for something that is outside our predefined limitations. So when we are talking about writing a new Interconnect-SPICE-like specification that is basically a subset of what the existing languages are already offering, I ask myself the question: Does the world really need another limited, specialized, and inflexible modeling language, most of whose features (plus more) already exist in other languages? (I know, there are a few novel technical features we want to put into this new language which don't exist elsewhere, but there may be other ways to make those available for ourselves). As a (ridiculous) analogy I would ask the question, would it make sense to write a new standard for a programming language which is C-like, but is limited to draw only rectangles on the screen because we decided that for our purpose the world is rectangular? I am sure we will be able to draw beautiful rectangles on our screens, but if someone comes along and needs to draw them with rounded corners, they will start complaining. So was it worth it to invent this new standard language as opposed to figure out ways to make the more universal C language available for our purpose? Arpad =============================================================== -----Original Message----- From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff Sent: Thursday, June 26, 2008 10:53 PM To: 'IBIS-ATM' Subject: [ibis-macro] Re: Question on seeting the EMD direction Arpad, Not sure what you're getting at with your last point. I think the first challenge we have with an interconnect modeling spec is defining the problem we're trying to solve, the intended applications and what assumptions we're willing to make. Drawing from an example earlier today, we need to state our assumptions about how things like temperature and process are represented. There are two fundamental approaches to modeling interconnect as I see it: 1) An electrical equivalent modeling approach, providing a simulation model that is precise and accurate enough for an intended purpose 2) A physical description approach, describing the actual materials and geometries so that simulation tools can extract their own electrical equivalent models as needed We've been talking about the first approach with EMD and ICM. One challenge with simulation is the tradeoff between speed and accuracy (actually, the tradeoff is between speed and precision, but that's another discussion). Model detail is one of the key enabling elements of increased *precision*, and thus always gets caught up in the argument. The usual challenge to a given level of modeling detail is "yeah, but your model doesn't represent such and such a physical effect, and therefore it isn't accurate enough". Here as before, we would be better served if we distinguished between precision and accuracy. The level of detail required is case-dependent, which is what makes these discussions so difficult. If you have a system that's close enough to the edge, physical effects that don't matter in 9 out of 10 systems will still be the difference between success and failure in that one case. If you try to create the system (or language) that can represent any possible case, you'll probably end up with a system (or language) that no one wants to use (which is what I think Mike was getting at). So now what? If I've followed the discussion correctly, thus far we've said we're interested in created a spec for modeling interconnect at the electrical level. I think we should spend some more time hashing out our mission statement - are we modeling interconnect for any purpose at all? Over what frequency range? For what purpose (for example, if we said we wanted to model serial links for periods < 10**17 bits, how big a factor would temperature variation be)? The practical aspect here is that the more succinctly we can define our mission statement, and the more clearly we can articulate intended applications and fundamental assumptions, the greater our chance for success will be. If we can't clearly articulate these things, then we're taking on a very big task indeed. Todd. Todd Westerhoff VP, Software Products SiSoft 6 Clock Tower Place, Suite 250 Maynard, MA 01754 (978) 461-0449 x24 twesterh@xxxxxxxxxx www.sisoft.com --------------------------------------------------------------------- IBIS Macro website : http://www.eda.org/pub/ibis/macromodel_wip/ IBIS Macro reflector: //www.freelists.org/list/ibis-macro To unsubscribe send an email: To: ibis-macro-request@xxxxxxxxxxxxx Subject: unsubscribe --------------------------------------------------------------------- IBIS Macro website : http://www.eda.org/pub/ibis/macromodel_wip/ IBIS Macro reflector: //www.freelists.org/list/ibis-macro To unsubscribe send an email: To: ibis-macro-request@xxxxxxxxxxxxx Subject: unsubscribe
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