Re: reset_event

Philipp, All,

You raise some interesting questions.

Re. when reset_event() is notified, I cannot see that it makes any
difference "when" it is notified relative to the reset action (assuming
notify() is called from reset(), of course, which it has to be) because
the effect of an immediate event notification is merely to make some
processes runnable. Any such processes will not actually be executed until
the current process yields (the one calling reset()).

When sc_pause() is called (or sc_stop() is called, for that matter) all
kinds of activity can indeed be scheduled before the calling process
yields. This activity includes event notifications (immediate, delta, and
timed) and process control calls (including immediate ones). Any activity
scheduled for the current evaluation phase will be executed before
simulation is paused or stopped, so there could be a long chain of
immediate notifications. sc_get_status() == SC_RUNNING during such
execution. On return from sc_start(), the set of runnable processes will
be empty, although there may exists update requests and delta
notifications.

When sc_start() is called again, the set of runnable processes will still
be empty, so the schedule will jump to processing request_updates and
delta notifications. We must specify that the delta_cycle count shall only
get incremented once between evaluation phases across the pause.

After return from sc_start() the main scheduler loop is not running,
although request_update() may be called to schedule update requests.

We do need to consider which process control methods may be called when
simulation is paused:

suspend - yes?
resume - yes?
disable - yes?
enable - yes?
sync_reset_on/off - yes?

kill - no? (permitted during elaboration, but during elaboration there is
no call stack to unwind)
reset - no? (permitted during elaboration, but during elaboration there is
no call stack to unwind)
throw_it - no! (may only be called from a process)

In other words, I am proposing that the immediate semantics of the process
control methods can only be executed during simulation.

After calling sc_pause() or sc_stop(), simulation is still running until
return from sc_start(). Right now there is no way to ask the kernel
whether sc_pause() or sc_stop() have been called. It is legal (a warning)
to call sc_stop() more than once. So, what should happen if sc_stop() is
called after sc_pause() or sc_pause() after sc_stop() before the calling
process has yielded?

Should sc_stop() take precedence over sc_pause()?

Do we want to add:

        bool sc_stop_called() const;
        bool sc_pause_called() const;

Thanks,

John A

From:
"Philipp A. Hartmann" <philipp.hartmann@offis.de>
To:
john.aynsley@doulos.com
Cc:
bpriya@cadence.com, systemc-p1666-technical@eda.org
Date:
12/11/2010 23:46
Subject:
Re: reset_event

John, Bishnupriya,

I agree with having immediate notification of reset_event. We should
probably require, that this event is notified "after" the reset action
has been performed, though.

But I'm somewhat puzzled about the interaction of sc_pause and the
reset/terminated events. Due to the immediate semantics and the
immediate notification of these events, all kinds of model activity
could be triggered during SC_PAUSED, when processes are reset from
within sc_main.

  This feels indeed worrisome to me, as Bishnupriya put it in an earlier
mail. Do we need to require, that this implicit/immediate evaluation
phase at least sets the status back to SC_RUNNING? Or do we want to
prohibit this use of kill/reset/throw_it from in between calls to
sc_start?

Thanks,
Philipp

On 12/11/10 16:40, john.aynsley@doulos.com wrote:
> Bishnupriya,
>
> I am just trying to pin down the semantics of reset_event().
>
> Every flavor of reset, namely
>
> * reset()
> * resumption while in the synchronous reset state
> * async_reset_signal()
>
> is ultimately equivalent to a call to reset() happening during an
> evaluation phase. We want this to cause the notification of the event
that
> will be returned by the new method reset_event(). I can see two
> possibilities:
>
> * The reset event is notified using an immediate notification, in which
> case any processes sensitive to the reset event will become runnable in
> the same evaluation phase in which reset() is called
>
> or
>
> * The reset event is notified using a delta notification, in which case
> any processes sensitive to the reset event will become runnable one
delta
> cycle later.
>
> The immediate notification feels right to me.
>
> What do you think?
>
> Thanks,
>
> John A
>
>
>

-- 
Philipp A. Hartmann
Hardware/Software Design Methodology Group
OFFIS Institute for Information Technology
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