After agreeing strongly that we should forbid multiple triggerings of the clock of an assertion or a clocking block within a given timestep, I find myself having second thoughts. In Specman land, there is a commonly used approach in which a verification environment can exercise an untimed or even a null DUT in zero time. This can be very useful when verifying untimed functional models, and when checking-out the behavior of a testbench without a live DUT present. Each new round of activity in the verification environment happens in the SAME timeslot. It's not exactly the same, but there is a reasonably close analogy between Specman's behavior and the way a testbench executes in Reactive - it executes atomically with respect to the Active DUT, but can plant new events in the Active regions of the same timeslot, starting a whole new round of activity at the same moment of simulation time that, potentially, can schedule further activity in the Reactive region of the same timeslot. If we outlaw multiple triggerings of assertion or clocking in a given timeslot, this possibility is out of reach because we demand that clock events be separated in time - be in separate timeslots. I'm not sure right now whether I think this is important, but it's certainly something I have not heard discussed so far and it may be relevant for people using SV to implement and verify untimed functional models. At the very least, it provides a motivation for allowing the use of #1step and #Nstep as procedural delays - they could capture the notion of "move to a new timeslot without worrying about how much you advance simulation time". -- Jonathan Bromley, Consultant DOULOS - Developing Design Know-how VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, Hampshire, BH24 1AW, UK Tel: +44 (0)1425 471223 Email: jonathan.bromley@doulos.com Fax: +44 (0)1425 471573 Web: http://www.doulos.com The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.Received on Tue Feb 6 12:45:52 2007
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