Re: sc_event naming: Cadence position on proposed extension

All,

So we seem to be splitting into a few camps re. the event naming proposal.

In our timed-honored tradition, let's take a straw poll just to see where
everybody stands on this issue.

* Option 1 - Do nothing. Do not include event naming in this round of
standardization
* Option 2 - The Cadence proposal. Add named events, but named events can
only be children of modules or processes, not arbitrary sc_objects.
* Option 3 - The Synopsys proposal. Extend 2 such that sc_events, but only
sc_events, can be children of arbitrary sc_objects
* Option 4 - Something else.

"Votes" please (not legally binding)

I already have (but feel free to change your "vote")
* Option 1 - Tor
* Option 2 - Bishnupriya, John, Jerome
* Option 3 - Martin

This is getting urgent, so please respond!

Thanks

John A

From:
Martin Janssen <Martin.Janssen@synopsys.com>
To:
"john.aynsley@doulos.com" <john.aynsley@doulos.com>
Cc:
"systemc-p1666-technical@eda.org" <systemc-p1666-technical@eda.org>
Date:
23/11/2010 14:01
Subject:
Re: sc_event naming: Cadence position on proposed extension

John,

A lot of nice words from Bishnupriya, but the only objection against our
extension
proposal is hierarchical naming of objects, which is not part of our
proposal, and
for good reason.

But does this mean that we should do a lousy job on hierarchical event
naming?
Or, put differently, should we treat events as first class citizens or
not?

Let's take a look at the current objects types. We have modules and
processes,
which are the most important object types when modeling and simulating
with
SystemC. Their hierarchical name is just perfect, and also in other
regards we
can say that these object types are indeed first class citizens. The other
object
types, such as ports, exports, primitive channels, are already in the
"poor objects"
(or second class citizens) category.

Enter named events. We already decided not to make them objects, but to
treat them somehow like objects. In which of the two above categories
(first
class citizens or second class citizens) do events belong? Bishnupriya is
saying that we should put them with the second class citizens, and do as
poor a job at naming them. But events _are_ first class citizens that
belong
with modules and processes. During simulation processes and events are
at center stage.

So my question is: why not treat events as we do modules and processes?

An implementation that has been out there for 2 years, on its own, cannot
be
enough reason for unamended standardization.

-Martin

On 2010-11-22 11:35, Bishnupriya Bhattacharya wrote:
John, All,
 
Over the past few days, within Cadence, we have carefully reviewed the
SNPS extension to the Cadence event naming proposal. Our position is as
below. There is strong agreement within Cadence on this position,
including from Stuart .
 
First, about allowing objects to parent other objects, there are certainly
issues (as several of you have pointed out) if we try for an ambitious
scheme to arbitrarily change the object hierarchy at run-time. However,
that is not our intent. We're trying to explore if we can carve out a
small subset that will be useful. We're not envisaging a dynamic module
hierarchy. Any object hierarchy changes will be restricted to elaboration
time only.
 
So, what is the motivation? One thing that comes to mind is a natural
grouping of things to better express the intent of a class, and prevent
"leakage" of internal implementation objects to the outside of this class.

Consider an aggregate class like the TLM2 simple_target_socket. It has a
number of other objects and events inside it - these are all internal
implementation artifacts of this socket. Today all of these internal
objects/events end up in the parent module's scope. The output of
get_child_objects() and get_child_events() on a target module that owns a
simple_target_socket is given below.
 
top.target.socket
top.target.socket_port_0
top.target.m_peq_0
top.target.b2nb_thread_0
top.target.peq_with_cb_and_phase_0
top.target.fec_0
top.target.event_0
top.target.event_1
top.target.event_2
top.target.event_3
Everything besides the target socket itself, does not really belong to the
parent module's scope; the rest is useless clutter that a user never wants
to see. It is safe to say that the simple_target_socket class does not
intentionally want to expose these internal implementation artifacts, but
today it has no choice but to do so. With the SNPS extension proposal, the
events will now go out of this list - the poor objects will be left behind
 
top.target.socket
top.target.socket_port_0
top.target.m_peq_0
top.target.b2nb_thread_0
top.target.peq_with_cb_and_phase_0
top.target.fec_0
 
This is not consistent. It does not feel right that events will end up
with the property that they can be grouped more hierarchically, but
objects can't. As things stand today (or rather I should say with the
Cadence proposal), things are not perfect, but at least an user can expect
consistency when constructing an user-defined object wrt scope of internal
objects and events. With the SNPS extension, that is no longer true. It is
as if events have become more of a first class citizen than objects.
 
We all agree that a proper "fix" for this - such that objects can also be
children of other objects in some restricted, but useful fashion - is not
simple. Many issues need to be considered, especially wrt adjusting
existing object's ctor, and other issues that Philip has raised.
Realistically speaking there isn't time in this round to consider all the
ramifications, and arrive at a solution (or conclude one is not possible).

 
Given that, we feel it will be inappropriate to only standardize the
object-owning-events feature, and leave things in a half-baked state. We
do not buy the argument that since this feature pertains to event naming
it will make it to this round - we DO need to consider the ramifications
of proposed solutions to the rest of the ecosystem. We feel it is more
appropriate for the LRM to leave kernel event naming as
implementation-defined in this round, and include this feature as an
addition in the next round if it is so deemed. We're opposed to rushing
something into the LRM that leaves things in an inconsistent state without
having the time to consider the complete problem.
 
Leaving this aspect implementation-defined in p1666-2010 allows each
vendor (including the OSCI ref sim) to experiment with developing a sane
object/event naming and parent/child relationship hierarchy while
remaining compliant with the 2010 standard. In 1666-2012 (or whenever the
next round is) we can then propose standardizing that which we have
previously implemented and tested.
 
We would like to hear what others have to say on this topic.
 
Thanks,
-Bishnupriya
 
----------------------------------------------------------------------------------------------------------------------------------------------------

     Bishnupriya Bhattacharya | Software Architect - Virtual System
Platform | Cadence
     P: +91.80.4184.1197 www.cadence.com
----------------------------------------------------------------------------------------------------------------------------------------------------

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