LRM clarification re sc_start

All,

The LRM needs clarifying with respect to the corner case where the very first call to sc_start has a zero-valued time argument. The description of sc_start(0) says it runs eval-update-delta, which is inconsistent with the text descibing the first call to sc_start.

John A

-----"Philipp A. Hartmann" <philipp.hartmann@offis.de> wrote: -----
To: john.aynsley@doulos.com
From: "Philipp A. Hartmann" <philipp.hartmann@offis.de>
Date: 01/21/2011 11:58AM
Cc: bpriya@cadence.com, Andy Goodrich <acg@forteds.com>, systemc-p1666-technical@eda.org
Subject: sc_time_to_pending_activity example (was Re: Another lib to check.)

John,

comments below.

On 21/01/11 11:54, john.aynsley@doulos.com wrote:
>
> Before the initialization phase there are no runnable processes.  There
> may or may not be pending update requests or notifications. If not,
> sc_time_to_pending_activity() should return sc_max_time() during
> elaboration.

Works for me.  This is then consistent with sc_pending_activity(), which
is a Good Thing.

> If there is no pending activity when sc_start() is called, which is the
> default, sc_time_to_pending_activity() should return sc_max_time. I agree
> with the need for the workaround. Maybe we should add a note to the LRM
> pointing this out, but I don't think it is a big deal.

I think in a note, the issue may be too difficult to describe.
What about an example for the step-wise simulation?  This could
illustrate the motivation for these functions in general:

int sc_main( int, char*[] )
{
  // instantiate design
  ...

  // elaborate design
  sc_start( SC_ZERO_TIME );

  // run step-wise simulation
  while( sc_pending_activity() ) {

    // run single (time) step
    sc_start( sc_time_to_pending_activity() );

    // run remaining current deltas (optional)
    while( sc_pending_activity_at_current_time() ) {
      sc_start( SC_ZERO_TIME );
    }
  } // pending activity

  return 0;
}

Greetings from Oldenburg,
  Philipp

> From:
> "Philipp A. Hartmann" <philipp.hartmann@offis.de>
> To:
> john.aynsley@doulos.com
> Cc:
> Andy Goodrich <acg@forteds.com>
> Date:
> 21/01/2011 09:52
> Subject:
> Re: Another lib to check.
>
>
>
> John,
>
> see below.
>
> On 21/01/11 10:08, john.aynsley@doulos.com wrote:
>> "Update requests, timed notifications, and delta notifications may be
>> created before the first call to sc_start,
>> but immediate notifications shall not be created before the first call
> to
>> sc_start."
>
> Since the initialisation phase is special, we need to consider the
> initially running processes as well.  The set of these processes can not
> be (finally) determined before the end of elaboration.  But in the
> majority of cases, there will be processes being run in the first delta.
>
>   If there are no update requests, delta notifs or timed notifications
> set up before the first call to sc_start, should
> sc_time_to_pending_activity() return sc_max_time() before the end of
> elaboration?
>
>   In the attached example, the first (external) activity is at 10 ns.
> But there's a process scheduled at the beginning. The main loop in
> sc_main is essentially:
>
>   sc_start( SC_ZERO_TIME ); // elaborate -- needed to avoid segfault
>   while( sc_time_stamp() < sc_max_time() )
>   {
>     sc_start( sc_time_to_pending_activity() );
>   }
>
>   The first sc_start( SC_ZERO_TIME ) would be _required_, if the intent
> is to run the simulation step-wise, since otherwise some steps may be
> skipped due to additional notifications being created in the first
> evaluation phase.
>
>   I think, I can live with this caveat, since there's an easy
> workaround.  But still it may be surprising?
>
> Greetings from Oldenburg,
>   Philipp
>
>> So there could be timed notifications before sc_start => time-to-pending
>>
>> 0
>>
>> John A
>>
>>
>>
>> From:
>> Andy Goodrich <acg@forteds.com>
>> To:
>> "Philipp A. Hartmann" <philipp.hartmann@offis.de>
>> Cc:
>> John Aynsley <john.aynsley@doulos.com>
>> Date:
>> 20/01/2011 22:48
>> Subject:
>> Re: Another lib to check.
>>
>>
>>
>> The issue with sc_time_to_pending_activity() as coded is that there are
>> structures within the simulation context that have not been fully
>> initialized, so some of the checks that I need to perform cause illegal
>> accesses. I can use a call to sc_is_running() to detect that is the
> case.
>> Then I can return a value if the simulation is not running. should that
> be
>> SC_ZERO_TIME?
>> The vcproj issue was probably caused by my doing a cp command to install
>
>> it, I'll try just unzipping in place.
>> Sorry about missing the patch, I'll add the code.
>>
>> Andy
>>
>> On Jan 20, 2011, at 2:03 PM, Philipp A. Hartmann wrote:
>>
>> Andy, John,
>>
>> when toying with sc_time_to_futute_activity() and the step-wise
>> simulation, I've stumbled over a segfault.  Probably, since I call this
>> function _before_ the elaboration has finished.
>>
>> John, do you think this needs to be clarified in the LRM?
>> Or can we derive from some other property, that the function should
>> return SC_ZERO_TIME in that case?
>>
>> Andy, two minor things wrt the patches I sent you:
>>
>>  - float constructors seem to be missing in sc_ufix.h
>>    (patch attached)
>>
>>  - SystemC.vcproj has unix file endings, although you
>>    _did_ ask for a verbatim copy :-(
>>    (zipped version attached, hopefully preserving EOLs)
>>
>> Greetings from Oldenburg,
>>  Philipp
>
>
>

-- 
Philipp A. Hartmann
Hardware/Software Design Methodology Group
OFFIS Institute for Information Technology
R&D Division Transportation ú FuE-Bereich Verkehr
Escherweg 2 ú 26121 Oldenburg ú Germany ú http://offis.de/en/
Phone/Fax: +49-441-9722-420/282 ú PGP: 0x9161A5C0 ú Skype: phi.har
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