systemc: Remove a redundant error check.

If the check doesn't abort the port binding in progress, it will be
reported twice.

Change-Id: I691ebd0f1598193f861c6085341dcd2fb05dd210
Reviewed-on: https://gem5-review.googlesource.com/c/13327
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Fix how the maximum size is computed for sc_ports.

Change-Id: I073eb16cbeb892f24ac3860daca056ed2fb09086
Reviewed-on: https://gem5-review.googlesource.com/c/13325
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Change how signal based resets work.

The previous implementation used the value changed event to track when
signals changed value, but there were a couple problems with this
approach. First, this piggybacked on the sensitivity mechanism in some
ways, but diverged in others. The sensitivity didn't notify a process
when it was satisfied like other sensitivity types would, and it also
ignored whether the process was disabled.

Second, the value_changed_event is notified by a signal instance as a
delta notification, but reset signals are supposed to act immediately.
That means they should happen before all delta notifications, or in
other words all delta notifications should see the reset status of a
given process. That's particularly important in the case of wait(int n)
where setting the reset clears the reset count, and the count is
checked when determining whether or not to wake up a process when its
sensitivity is satisfied, potentially by a delta notification.

Third, by removing the middle man and not trying to repurpose the
sensitivity mechanism, the code gets simpler and easier to understand.

Change-Id: I0d05d11437291d368b060f6a45a207813615f113
Reviewed-on: https://gem5-review.googlesource.com/c/13294
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add an sc_gem5::Port destructor.

This destructor just removes the port from the list of all ports.

Change-Id: I809b529540c2946d20aeb8d64467d77dc94a7a96
Reviewed-on: https://gem5-review.googlesource.com/c/13288
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add missing sc_interface::register_port, and add calls to it.

This function is standard and supposed to be on sc_interface, but it
was somehow left out. This change adds it, and makes sure it's called
by the port binding code. The default implementation does nothing, as
it's supposed to according to the spec.

Also note that only the ports farthest from the interfaces are suppose
to call register_port. As the port bindings are completed, we keep
track of whether a port has been bound to another port. If it has, the
source port is farther from the interfaces than the target port (since
it has to go "through" the target port to get to them, and so the
target port should not call register_port.

Change-Id: Ia98f9ff364385fd1699d88a1d99787d205816a08
Reviewed-on: https://gem5-review.googlesource.com/c/13199
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Change how the timing of binding ports works.

In the Accellera implementation, interfaces are bound to ports
immediately if no ports have been bound, and otherwise saves them for
later along with the ports. The existing implementation would save
all interface and port bindings to finalize at the end of elaboration.

This seems like pointless complexity, but it's necessary to get the
output to match in the tests.

Change-Id: Ib82d324ee2be9e56e6a41561611c7fca4f4f4e72
Reviewed-on: https://gem5-review.googlesource.com/c/13196
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement signal based resets.

The implementation is based on sc_event sensitivities.

Also of note is that the way reset works in the Accellera
implementation isn't consistent with the spec. That says that
wait(int n) is supposed to be equivalent to calling wait() n times,
assuming n is greater than 0.

Instead, Accellera stores that count and then doesn't wake up the
process until the count is 0, decrementing it otherwise.

That means that when the process is in reset, it won't actually reset
for those intermediate wait()s which it would if wait() was called
repeatedly. Also, oddly, when a reset becomes asserted, it will clear
the count to 0 explicitly. That may have been an attempt to make the
behavior of wait(int n) match the spec, but it doesn't handle cases
where the reset is already set when wait(int n) is called.

Change-Id: I92f8e9a128e6618af94dc048ce570a4436e17e4b
Reviewed-on: https://gem5-review.googlesource.com/c/13186
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add an error check whether an interface is alread bound to a port.

Change-Id: I06e3484176c0c06daa28f7be0ed8437b3b15ddb2
Reviewed-on: https://gem5-review.googlesource.com/c/12816
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Rework how delayed sensitivities are handled.

Make BindInfo into a more general purpose Port class which mirrors
sc_module and Module, sc_object and Object, etc. This tracks multiple
bindings internally, and also pending sensitivities. Keep a global
list of ports which are added in reverse order to match Accellera, and
which is iterated over to finalize binding and for phase callbacks.
This is as opposed to doing it one module at a time, and is to better
match Accellera's ordering for the regressions.

Also the sensitivity classes are now built with factory functions,
which gets around problems calling virtual functions from their
constructors or forgetting to having to have extra boilerplate each
place they're constructed.

The port class also now finalizes port or event finder sensitivities
when its binding is completed, unless it's already complete in which
case it does so immediately.

Change-Id: I1b01689715c425b94e0f68cf0271f5c1565d8c61
Reviewed-on: https://gem5-review.googlesource.com/c/12806
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>