#3. "error to use a sample argument" should read "error to
use a sample formal".
OK.
#4. The last example needs a "ref" added in the covergroup
arguments, like so: "covergroup C1 (ref int v)".
No.
That’s the whole point of the example.
Users
may think that it’s OK to use the “v” covergroup argument by
the constructor (to set the weight option) and the “v” sample
formal by the definition of the coverpoint., The rule is intended to
avoid this
ambiguity.
DCS: In your example "v" was a coverpoint expression. If
someone were to write it passing "v" into the constructor, they would
write it as "ref int v". You are passing "b" -- assigned
to weight -- through the sample method, a different illegality.
You’re
right. I forgot to add to the example, it should
have read:
covergroup
C1
(int v) @ function sample
(int v, bit b); //
error (v)
coverpoint v;
option.per_instane
= b; // error: b may only designate a
coverpoint
option.weight
= v; // error: v
is ambiguous
endgroup
#5. Just for people to consider, we are expecting the following to be
legal (with our preferred syntax)?
int a;
covergroup ct (ref int b) function sample(int c);
coverpoint a + b + c;
endgroup
Yes.
We agree. Awkward, but legal nonetheless.
#6. A host of issues around
sample
arguments. One thing that occurred to us -- without, I'll note,
Gordon's
blessing! -- is that we could possibly allow this:
int a;
covergroup ct function sample(ref int x = a);
coverpoint a;
This would allow event-based
sampling to occur as well
as procedural sampling, let's say with this syntax (which I know would
be a
change from the proposal):
covergroup ct function
sample(ref int x = a) @(e);
With event-based sampling, the
default arguments would
be used, which as you see cause "a" from the enclosing scope to be
sampled. It wasn't clear from Mike's original e-mail whether the
override
was expected to be optional (used occasionally) or required (used
always).
I am
very uncomfortable with this change. The current proposal makes it
clear that
there are two mutually exclusive ways to trigger a covergroup: via an
events
(or block event) or procedurally through the sample method. Otherwise,
there
are other issues like “strobe” sampling that rear their ugly head.
DCS: I'm OK disallowing what I suggested; it does make it simpler to
disallow
it. I'll comment on "strobe" later in the thread, though.
If default arguments are used, what restrictions are there? Can they
be
covergroup formals, like this?
covergroup ct (ref int a)
function sample(ref int x =
a);
Good
point. I would say no. Covergroup formals should not be visible in the
scope of
default arguments.
Can they be non-static class
properties for an
embedded covergroup?
Yes.
Any reason to disallow them?
What about "output" arguments? While this sounds nonsensical,
someone might find a use for something like this:
function int f(output o, input
i);
o = 2*i;
return o;
endfunction
covergroup ct function sample(output o, input i);
coverpoint f(o,i);
endgroup
As you
say, “output” arguments are nonsensical. Do we need an explicit
error rule? Is there any plausible expectation on the part of users?
DCS: I have no idea whether users would expect this or not -- users
frequently
surprise me -- but an explicit sample arguments list opens up the
possibility. We need language in the proposal to disallow what we
believe
makes no sense.
I’m
OK with such a
restriction. But, shouldn’t we add the same for covergroup formals (it
also makes no sense there).
Finally, what about a null
argument list to
sample? That sounds to me like it should be disallowed.
The
current BNF allows it and I see no problem for an overridden method to
have the
same signature as the default method. In a way the proposal is saying
that
omitting the coverage_event is the same as an explicit “covergroup
<name> @ function sample();”
-- David Scott, Mentor
Graphics
Arturo Salz wrote:
I've uploaded a proposal for Mantis 2149. Please review.
Arturo
-----Original Message-----
From: owner-sv-ec@eda.org On Behalf Of Michael Burns
Sent: Wednesday, October 24, 2007 4:38 PM
To: SV_EC List
Cc: John Havlicek
Subject: [sv-ec] Mantis 2149 - Covergroups sample method with arguments
Mantis 2149 - Covergroups sample method with arguments has been
submitted
describing what we'd like to see in a solution for the covergroup sample
issue I
raised a week or two ago.
--Mike Burns