Re: [sv-ec] input skew

I got diff between 1step and #1 where unit != step.
But what if unit == step?
Lest have an example

    `timescale 1ns/1ns
    module top;
         bit clk;
         int a,b,c;
         assign b=a;
         assign c=a;
         initial repeat(20) #5 clk = ~ clk;
         clocking cb @(posedge clk);
             input a;
             input #1 b;
             input #10 c;
         endclocking
         initial begin
             forever #1 a++;
         end
         always @(cb)
             $display($time, cb.a, cb.b, cb.c);
    endmodule

What would be the 1st line of output:

       KERNEL: 5 4 3 0
    or
       KERNEL: 5 4 4 0

What would be the 2st line of output:

       KERNEL: 5 14 13 4
    or
       KERNEL: 5 14 1 4 5

 From text I would say that 2nd results are ok, but from common sens I
would say that 1st one

DANiel

On 6/22/2011 10:46 AM, Bresticker, Shalom wrote:
>
> Jonathan, please note Mantis 1247.
>
> Regards,
>
> Shalom
>
> *From:*owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] *On Behalf Of
> *Jonathan Bromley
> *Sent:* Wednesday, June 22, 2011 11:32 AM
> *To:* Daniel Mlynek; sv-ec@eda.org
> *Subject:* Re: [sv-ec] input skew
>
> h Daniel
>
> I think you may be confusing "time unit" and "time step". However, I
> agree that the phrase "the time step skew time units prior" is quite
> hard to parse. In that phrase, "skew" is a placeholder for the value
> in the #skew sampling delay, so we could rewrite it as "the time step
> that occurred _skew_ time units prior to the clocking event".
>
> Consequently, input#1 sets the skew to one time UNIT, whereas
> input#1step sets the skew to one time STEP.
>
> The intent of #1step is to sample values as they were _immediately
> before_ the current moment in simulation time. Since a time step is a
> point in simulation time where there are some events, it's clear that
> there can be no activity (no value changes, no events) between the
> previous timestep and the current time step. So it doesn't matter at
> what absolute time the previous time step occurred. It could be as
> recent as one time-resolution before the current time, but it might be
> long before that.
>
> In any case, #1step sampling requires the clocking block to sample
> values in Postponed of the immediately previous time step. This is
> exactly equivalent to sampling in the Preponed region of the current
> time step, because there can be no value changes in the time between
> those two timesteps. That's quite satisfying, because it means
> input#1step sampling reliably gives the same values that are seen by
> assertions. [Question for VPI experts: is there any way that VPI
> callbacks could break that equivalence?]
>
> Another question for everyone: I used to think that there was a subtle
> distinction between "time slot" and "time step", but in the 2009 LRM
> they appear to be used interchangeably. Neither term appears in the
> Glossary. "time slot" is explained pretty thoroughly in clause 4, but
> "time step" doesn't appear to be defined anywhere. The assertions,
> coverage and VPI clauses seem to favour "time step", whereas clause 4
> predominantly uses "time slot". Is there a case for making an
> editorial change to use the same term everywhere?
>
> Jonathan Bromley
>
> ------------------------------------------------------------------------
>
> *From:*Daniel Mlynek <danielm@aldec.com.pl>
> *To:* "sv-ec@eda.org" <sv-ec@eda.org>
> *Sent:* Wednesday, 22 June 2011, 7:52
> *Subject:* [sv-ec] input skew
>
>
> /LRM senstences:/
>
> /1. A 1step input skew allows input signals to sample their
> steady-state values in the time step immediately before the clock
> event (i.e., in the preceding Postponed region)./
>
> /2.If the input skewis not an explicit //#0//, then the value
> sampled corresponds to the signal value at the Postponed region of
> thetime step skew time units prior to the clocking event/
>
> /sugest that #1step and #1 input skew are the same/
>
> /So is clocking event occurs in time 10.
> Then sampled value is taken from postponed region of time 9 in both cases
> Is it how it should work If so then 1step is redunand./
>
> /
> DANiel/
>
>
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