That intent of that sentence was to explain the semantics of the edge specifier, that is, what does it mean when the skew is simply an edge - such as input. Likewise, the "number" in that sentence refers to the delay control specification, such as #3. I agree that it could be worded better. Possibly saying something like "When the clocking event specifies simply an edge, and no delay control, the skew becomes the specific edge of the clocking signal." Arturo -----Original Message----- From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Steven Sharp Sent: Monday, August 10, 2009 12:40 PM To: sv-ec@eda.org Subject: [sv-ec] What is meant by "simple edge"? Clause 14.3 refers to the situation where a clocking block clocking event specifies a "simple edge". This term is not defined, nor is it used anywhere else in the LRM. The situation is required before you can use an alternate edge as a skew. So what was it intended to mean? My guess is that it refers to the situation where the clocking event is simply an edge (posedge, negedge, edge or the implicit "any change" that is indicated by the lack of an explicit edge) applied to an expression, and nothing else. It clearly must exclude any composite expression with multiple events separated by event-OR. I would assume that it also excludes any event conditioned with "iff", but this is not as clear. I assume this partly because it doesn't seem to match the description "simple edge". Also, if an event conditioned with "iff" were allowed, it doesn't seem clear what the skew would be. Would you keep the iff condition with the new edge, or remove it? Since this is unclear, it seems that this situation is more complex than was intended to be allowed. BTW, the wording of this sentence in the LRM is also confusing. It says "When the clocking event specifies a simple edge, instead of a number, the skew can be specified as the specific edge of the signal." It seems to be saying that the simple edge is instead of a number, which makes no sense. The clocking event cannot be a number. Only on repeated reading did I decide that it was saying that instead of the skew being specified as a number, the skew can be specified as the specific edge of the signal. This would have been clearer if that phrase were moved to the end of the sentence, where it is more clearly associated with the second half: "When the clocking event specifies a simple edge, the skew can be specified as the specific edge of the signal, instead of a number." This still seems to be slightly incorrect. The BNF allows specifying an edge AND a number. I presume that this gives an additional skew from the specific edge of the signal. So it really ought to say "When the clocking event specifies a simple edge, the skew can be specified as the specific edge of the signal, in addition to a number." Can somebody clarify what was intended by this text? Steven Sharp sharp@cadence.com -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.Received on Mon Aug 10 15:08:31 2009
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