ext: Include SystemC 2.3.1 into gem5

In the past it happened several times that some changes in gem5 broke the
SystemC coupling. Recently Accelera has changed the licence for SystemC
from their own licence to Apache2.0, which is compatible with gem5.
However, SystemC usually relies on the Boost library, but I was able to
exchange the boost calls by c++11 alternatives. The recent SystemC version
is placed into /ext and is integrated into gem5's build system. The goal is
to integrate some SystemC tests for the CI in some following patches.

Change-Id: I4b66ec806b5e3cffc1d7c85d3735ff4fa5b31fd0
Reviewed-on: https://gem5-review.googlesource.com/2240
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/ext/systemc/README.md b/ext/systemc/README.md
new file mode 100644
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+Overview
+========
+
+This repository is a redistribution of the Accellera SystemC 2.3.1 library
+[[1]][sysc]. This distribution replaces Accellera's Autoconf build system with
+a SCons build system, which is very useful for integration of SystemC in other
+SCons based projects, e.g., gem5 [[2]][gem5].
+
+The repository contains all the source files from the Accellera distribution,
+but strips down the boost dependencies. All references to the boost library
+are replaced by calls to the C++11 STL. This repository also contains the
+TLM 2.0 protocl checker from Doulos [[3]][doulos].
+
+Build
+=====
+
+To build libsystemc-2.3.1.so, simply type scons. Optionally you can specify the
+number of jobs.
+
+```
+scons -j N
+```
+
+To build and link to SystemC from another SCons project, simply call the
+SConscript located in `src/`. Be sure to add `-std=c++11` to the `CXXFLAGS` of
+your environment and to export the environment as `'env'`. In case you build on
+OS X, you will need to add `-undefined dynamic lookup` to your `LINKFLAGS`.
+This is how a minimal SConstruct for your SystemC project could look:
+
+```python
+env = Environment()
+
+env.Append(CXXFLAGS=['-std=c++11'])
+if env['PLATFORM'] == 'darwin':
+    env.Append(LINKFLAGS=['-undefined', 'dynamic_lookup'])
+
+systemc = env.SConscript('<path_to_systemc>/src/SConscript', exports=['env'])
+env.Program('example', ['example.cc', systemc])
+```
+
+[sysc]: http://accellera.org/downloads/standards/systemc
+[gem5]: http://www.gem5.org/Main_Page
+[doulos]: https://www.doulos.com/knowhow/systemc/tlm2/base_protocol_checker/