systemc: Get rid of leftovers from unimplemented warnings past.

These warnings were removed when the functionality they warned about
was implemented, but there were some leftovers like unnecessary
includes and some helper functions which hid gem5 specific headers
from the ext directory.

Change-Id: Ic886ac0f1264687524e3a7b7eaab8836f318a5a2
Reviewed-on: https://gem5-review.googlesource.com/c/13398
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Switch to using predefined messages for channels.

Create and use predefined messages for channels which match the ones
Accellera uses.

Change-Id: I179214838bbd83604e50225926cdc6b5b1b16923
Reviewed-on: https://gem5-review.googlesource.com/c/13330
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Change how errors are handled in some constructors slightly.

Because SC_REPORT_ERROR usually causes an exception to be thrown, it's
easy to assume it will be the last thing executed in a function. It
might, however, be set up to do nothing, in which case the function
will continue to execute.

This change makes sure sc_prim will be set up properly even if errors
about the time a channel can be set up are ignored.

Also, if an exception is thrown while sc_port is being set up, the
corresponding Port object needs to be cleaned up. Rather than try to
intercept exceptions in the constructor and clean up properly, we'll
just make the allocation of the Port object be the last thing it does.
If the function exits early, then the Port pointer will still be
nullptr and nothing will need to be done.

Change-Id: If8f6f6b7e6830235fee3cd75625240b99e87dfbe
Reviewed-on: https://gem5-review.googlesource.com/c/13289
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add some additional error checks.

Change-Id: I19c5e6f1795c2777dbe7d210cfa01f6ced2020f3
Reviewed-on: https://gem5-review.googlesource.com/c/12815
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement the deprecated "timed_out" function.

This function requires some slightly annoying bookkeeping since it
doesn't just report whether the current process is running as a result
of a timeout, it reports whether it's running as a result of a timeout
*and* it could have been running from some other sensitivity instead.
Pure timeouts don't count as timeouts which makes it harder to handle
in a general way.

Change-Id: I533d97fe66d20d7b83aba80f2ef45a8944668070
Reviewed-on: https://gem5-review.googlesource.com/c/12608
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add a "changeStamp" value to the scheduler.

This value is incremented after each delta cycle's evaluate stage and
after timed notifications happen. Its value is used by some channels
to determine whether certain events happened within the previous update
phase to implement the "event()", "posedge()", and "negedge()"
functions.

Change-Id: I9a73f0b5007dcbb6a74da9d666f28da1930b9d3d
Reviewed-on: https://gem5-review.googlesource.com/c/12452
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement channel updates and rework the scheduler.

This change implements channel updates, and also reworks the scheduler
to delegate more to the gem5 event queue by taking advantage of
event priorities to ensure things happen in the right order. There's
a lengthy comment in scheduler.hh describes how that all works.

Change-Id: I5dee71b86b2e612bb720a4429f3a72e4b7c6d01f
Reviewed-on: https://gem5-review.googlesource.com/11710
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add the nonstandard timed_out function.

Change-Id: If14a5f98f03448c712827b7f92d2a36992541518
Reviewed-on: https://gem5-review.googlesource.com/11279
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Seperate the "external" header interface.

Most (but not all) of the SystemC headers are part of the "external"
interface that an existing, standard compliant module would include
through <systemc.h> or <systemc>. Since those follow slightly different
rules (relative includes, no gem5 includes), this change separates them
out so that they're easier to identify.

Also, this change moves the other files into a "core" subdirectory,
with the intention to add a "dt", aka data type, directory some time in
the future when those standard defined types are implemented.

Change-Id: Ida63f9cc0bc0431024d4dd691cc5b22b944a99a8
Reviewed-on: https://gem5-review.googlesource.com/10835
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>