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

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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