Re: [sv-ac] sv-ac: quick clarification questions of checker update regions

Tom,
Thus, in the following, z gets the value that x has in the RE-NBA region.
*rand* bit w; bit x;
 always_ff @clk
 // w updated in the Re-NBA region, gets value that x has in that region
(re-nba).
    z <= x;
On 3213, do we want to show examples with checker variables with and without
the *rand*, and the value they get? From my thread, I was thinking of
something like:
*checker* check(bit a, b, event clk, ...);
  *bit* x, y, z, v;
  *rand* bit r, w;
  *assign* x = a & b; // changed in the Reactive Region,
                    // a, b are checker inputs, and are current value
                                        // when x is updated.
 * always_comb*
    y = a & b; // // changed in the Reactive Region,
                    // a, b are checker inputs, and are current value
                                        // when x is updated
  *always_ff* @clk
    z <= !x; // z updated in the Re-NBA region, x sampled in the preponed
region.

   *always_ff* @clk
      r <= !w; // r gets the value that !w has in the RE-NBA region.
*endchecker* : check

Ben

On Tue, Jun 7, 2011 at 8:29 AM, Thomas J Thatcher <
thomas.thatcher@oracle.com> wrote:

> Hi Benm
>
> Rand variables are never sampled (well, according to 3213, they are
> "sampled", but the "sampled value" of a rand checker variable is the current
> value).
>
> Nothing changes otherwise
>
> Tom
>
>
> On 06/06/11 19:11, ben cohen wrote:
>
>> Tom, One more question; For the new proposal, what if x, y were *rand*
>> variables, is below correct on sampling and updates?
>> checker check(bit a, b, event clk, ...);
>> * rand bit x, y, z, v;*
>> always_comb
>> y = a & b; // legal, changed in the Reactive Region? always_ff @clk
>> // x sampled in the preponed region.
>> // z updated in the Re-NBA region
>> z <= !x; // endchecker : check
>>
>> module m; logic clk=0, a, b;
>> initial forever #10 clk=!clk;
>> check chk1(a, b, posedge clk); ... endmodule : m
>>
>> On Mon, Jun 6, 2011 at 3:28 PM, Thomas J Thatcher <
>> thomas.thatcher@oracle.com <mailto:thomas.thatcher@oracle.com>> wrote:
>>
>> Hi Ben,
>>
>> For IEEE 1800-2009, continuous assignments are not allowed in checkers.
>> So the assignment to x would not be legal, and it was not defined
>> when x would be sampled. Dmitry's proposal (3033) would allow
>> continuous assignments within checker, and they would update in the
>> Reactive region. So the assignment to x would take place in the
>> Reactive region.
>>
>> Non-blocking procedural assignments are currently updated in the
>> Re-NBA region. This does not change. Previously, in 1800-2009
>> non-blocking assignments could only reference checker inputs or
>> other checker variables assigned by non-blocking assignments. The
>> non-blocking assignments would see the sampled value of any checker
>> inputs, because all checker inputs were sampled, and it would see
>> the current value of any other checker variable. Dmitry's proposal
>> would change things so that checker inputs are not automatically
>> sampled. However, any variable referenced by the RHS of a
>> non-blocking assignments would be sampled.
>>
>>
>> So if Dmitry's proposal is enacted,
>> 1. x & y updated in the Reactive region
>> 2. z updated in the Re-NBA region, x sampled in the preponed region.
>>
>> Tom
>>
>>
>>
>> On 06/05/11 23:28, ben cohen wrote:
>>
>> Questions: or model shown below: 1) When is "x" sampled? Active
>> Region 2) In what region is "z" changed? In the Reactive?
>> 3) are my comments correct?
>> checker check(bit a, b, event clk, ...);
>> bit x, y, z, v;
>> assign x = a & b; // legal, changed in the Reactive Region?
>> always_comb
>> y = a & b; // legal, changed in the Reactive Region?
>> always_ff @clk
>> z <= !x; // , x sampled in active region? z changed in Reactive?
>> endchecker : check
>>
>> module m; logic clk=0, a, b;
>> initial forever #10 clk=!clk;
>> check chk1(a, b, posedge clk); ... endmodule : m Ben
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>

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