I agree, if you believe it is feasible to insert this change at the current time frame. Thanks, Dmitry -----Original Message----- From: Gordon Vreugdenhil [mailto:gordonv@model.com] Sent: Thursday, March 20, 2008 4:27 PM To: Korchemny, Dmitry Cc: sv-bc@server.eda.org; sv-ec@server.eda.org; sv-ac@server.eda.org Subject: Re: [sv-bc] RE: [sv-ac] RE: [sv-ec] Checkers & Formal Korchemny, Dmitry wrote: [...] > It might be more useful in terms of cross-vendor consistency > to define how simulators MUST select the values of unassigned > freevars. Even something trivial like assigning them all > the value zero or possibly having a separate RNG that is > used. Vendors could also extend things in other ways, > but having reasonably predictable cross-vendor behavior > would seem to be an important goal. > > [Korchemny, Dmitry] My concern here is potential backward > incompatibility. I don't see how to define RNG behavior in the current > time frame, though it is a natural thing to do in the future. Therefore > the only acceptable definition for cross-vendor consistency now is > assigning a default value to all free variables (e.g., o to bit > variables, and X to logic variables). If the RNG behavior is defined > later, the new behavior won't be backward compatible. What do you think? Hmm. X doesn't seem to be a good idea to me; that will essentially make it impossible to satisfy most semi-interesting dependent freevar assignment assumptions since computations involving X generally result in X. In other words, won't X results in most cases just end up causing most assertions to fail? That would seem to be an unfortunate result of standardizing on that approach. I don't think that the RNG approach is really that hard, is it? Why not just say that there is one system-wide RNG that is used for all freevar assignments and that such an RNG is assigned as though it were in a separate top-level module. That should, I think, preserve random stability even when the number of checkers changes within the design. In addition, since RNG results don't produce X or Z values, I think that the likelihood of having reasonable results is much higher. Gord -- -------------------------------------------------------------------- Gordon Vreugdenhil 503-685-0808 Model Technology (Mentor Graphics) gordonv@model.com --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.Received on Thu Mar 20 09:01:14 2008
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