RE: [sv-ec] Errata 238 and 240 and a suggestion for a BNF change

From: Surrendra Dudani <Surrendra.Dudani@synopsys.com>
Date: Mon Oct 04 2004 - 10:43:08 PDT
Hi Eugene,
Please see my response in comments.
Surrendra
At 12:40 PM 10/1/2004 -0700, you wrote:
Surrendra,
 
"Is your objective to allow a sequence expression anywhere a primary can be used? "
 
Yes. this makes the testbench portion itself complete. for example, sequences expressions can be used with 'if'.
I think you will agree that 'expect' already support this. So SV LRM already provides this feature, we are recommending to
extend it ( into what you called simulation evaluation).
 

The "expect" statement evaluates a property to be true or false. A sequence may be part of the property.

A sequence evaluation can fork of different threads of evaluation, creating in a way multiple processes, all of them possibly ending at different times, or failing at different times. Seems rather complex.

Why? To a verification engineer, writing self-checking testbench ( stimulus and checking ) is a requirement, on top of that,
additional Assertions can be added. If we make such a connection that 'simulation evaluation' is corresponding to stimulus,
'assertion evaluation' is corresponding to checking, then to a user, there is no boundary. And there shouldn't be. That's our
strong belief. In other words, we believe 'checking' doesn't have to be done by 'Assertion' code only.

Is your intention to use assertion syntax with different semantics?

 
Let's me if you'd like more information or example code. Hope you can vote for this errata ( 255).

Please give some concrete examples to clarify your ideas.

 
-Eugene
 

From: Surrendra Dudani [mailto:Surrendra.Dudani@synopsys.com]
Sent: Thursday, September 30, 2004 1:33 PM
To: sv-ec@eda.org
Subject: Re: [sv-ec] Errata 238 and 240 and a suggestion for a BNF change
Hi Eugene,
I'm having difficulty understanding the semantics of this proposal. In sv-ac we carefully and formally defined the semantics of sequence_expr so that there is a clear semantic boundary between simulation and assertion evaluation (This includes the observe region where assertions are evaluated). Is your objective to allow a sequence expression anywhere a primary can be used?
Can you please elaborate on the semantics?

Surrendra
At 11:34 AM 9/24/2004 -0700, you wrote:
The following suggestion is a follow-up to the discussion in the last sv-ec meeting on Errata 238 ( Pipelined value access in clocking block) and
Errata 240 ( Expression valuation in cycle delay), with comments from Arturo.
 
In summary, 238 and 240 should be replaced by this proposal. as you can see, the change is minimal, however it can bring benefits to users. From our
experiences, writing self-checking testbenches, with embedded assertions,  is a natural process. Checking is usually done in testbench, doesn't
have to be in code called "Assertions' only.
 
We'd like to hear your feedback, tells us why if you say no and try to convince us. If we agree, the goal is to put this into the first IEEE standard.
 
Below is a brief description:
 
We carefully examined the whole section 17, and found that the functions we requested on SV-EC 238 (Pipelined value access) and 240 (delayed expression) can also  be realized with 'sequence_expr' and $past system  tasks in section 17 Assertions.

We agree that the basic functionality can be somewhat achieved by using 17.16 (expect statement), but in terms of the flexibility, we still suggest to have 'sequence_expr' as a part of regular expression.
This provides an  extremely flexible mechanism to express the cycled sequences   anywhere in the program statement. For example, it can be used in the  conditional qualifier for 'if' and 'while' statements .
Given that the the assertion mechanism must be implemented, we don't see any major technical difficulty  to include it as part of the  primary.  This extension raises the SystemVerilog's expression capability to totally different level.

Suggested Revised  BNF:  to add sequence_expre to primary

<?/x-tad-bigger><?/fontfamily><?/smaller><?fontfamily><?param Times New Roman><?bigger>   A.8.4 Primaries

   primary ::=
     .
     .
     sequence_expr
<?/bigger><?/fontfamily><?smaller>
 
 
Cheers,
-Eugene




**********************************************
Surrendra A. Dudani
Synopsys, Inc.
377 Simarano Drive, Suite 300
Marlboro, MA 01752

Tel:   508-263-8072
Fax:   508-263-8123
email: Surrendra.Dudani@synopsys.com 
**********************************************



**********************************************
Surrendra A. Dudani
Synopsys, Inc.
377 Simarano Drive, Suite 300
Marlboro, MA 01752

Tel:   508-263-8072
Fax:   508-263-8123
email: Surrendra.Dudani@synopsys.com 
********************************************** Received on Mon, 04 Oct 2004 13:43:08 -0400

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