VHDL Issue Number: 0054 Classification: Language Definition Problem Language Version: VHDL-87 Summary: Is a signal active when one its drivers takes on the null transaction? Related Issues: None. Relevant LRM Sections: 12.6.1 Key Words and Phrases: Null transaction, active, driver Current Status: ISAC-Approved 1076-1993 Disposition: Closed (All Issues Completely Addressed) Disposition Rationale: LRM is clear now, as described in Section 12.6.2. Superseded By: N/A ----------------------- Date Submitted: 1989/02/10 Author of Submission: Doug Dunlop Author's Affiliation: Intermetrics, Inc. Author's Post Address: 4733 Bethesda Ave #415 Bethesda, MD 20814 Author's Phone Number: (301) 657-3775 Author's Fax Number: Author's Net Address: dunlop@inmet.inmet.com ----------------------- Date Analyzed: 1991/01/11 Author of Analysis: Paul Menchini (mench@clsi.com) Revision Number: $Revision: 1.9 $ Date Last Revised: $Date: 1995/05/13 19:34:42 $ Description of Problem ---------------------- Activeness for signals is defined in terms of activeness of drivers. Activeness of drivers is defined in terms of drivers "acquiring new values." Does acquiring a null transaction amount to acquiring a new value? Proposed Resolution ------------------- Yes. This makes sense and is what would be expected. VASG-ISAC Analysis & Rationale ------------------------------ The author is correct. A driver becomes active whenever, as a result of the advance of simulation time, a pending transaction in the driver becomes the current transaction. This statement is true whether or not the pending transaction is a null transaction. VASG-ISAC Recommendation for IEEE Std 1076-1987 ----------------------------------------------- Interpret the activeness of drivers in light of the above statement. VASG-ISAC Recommendation for Future Revisions --------------------------------------------- Change the first paragraph of Section 12.6.1 (on page 12-9) to read as follows. The text in all capital letters denotes the added text. As simulation time advances, the transactions in the projected output waveform of a given driver (see Section 9.2.1) will each, in succession, become the value of the driver. When a driver acquires a new value in this way, regardless of whether the new value is different from the previous value, that driver is said to be active during that simulation cycle. FOR THE PURPOSES OF DEFINING THE ACTIVENESS OF DRIVERS, A DRIVER ACQUIRING A VALUE FROM A NULL TRANSACTION IS ASSUMED TO HAVE ACQUIRED A NEW VALUE. A signal is said to be active during a given simulation cycle: (This added text is parallel to the text of Section 8.3.1.)