systemc: Partially implement the scheduler.

This change implements the "evaluate" part of the delta cycles, and
sketches out a function to run delta cycles and the initialization
phase. The kernel object now schedules an event at time zero which
runs the initialization phase.

Also, some small places which were stubbed out pending a way to check
the currently running process have been filled in now that that's
being tracked.

Change-Id: I6899569eb0195ff1c059fa4e68e90ef162b2f2df
Reviewed-on: https://gem5-review.googlesource.com/11709
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

13 files changed, 559 insertions, 73 deletions

diff --git a/src/systemc/core/SConscript b/src/systemc/core/SConscript
index f4d65060f..045300478 100644
--- a/src/systemc/core/SConscript
+++ b/src/systemc/core/SConscript
@@ -34,6 +34,8 @@ if env['USE_SYSTEMC']:
     Source('module.cc')
     Source('object.cc')
     Source('process.cc')
+    Source('process_types.cc')
+    Source('scheduler.cc')
 
     Source('sc_attr.cc')
     Source('sc_event.cc')
diff --git a/src/systemc/core/kernel.cc b/src/systemc/core/kernel.cc
index 288a037cc..82281c085 100644
--- a/src/systemc/core/kernel.cc
+++ b/src/systemc/core/kernel.cc
@@ -28,12 +28,23 @@
  */
 
 #include "systemc/core/kernel.hh"
+#include "systemc/core/scheduler.hh"
 
 namespace SystemC
 {
 
-Kernel::Kernel(Params *params) : SimObject(params)
+Kernel::Kernel(Params *params) : SimObject(params), t0Event(this) {}
+
+void
+Kernel::startup()
+{
+    schedule(t0Event, curTick());
+}
+
+void
+Kernel::t0Handler()
 {
+    ::sc_gem5::scheduler.initialize();
 }
 
 } // namespace SystemC
diff --git a/src/systemc/core/kernel.hh b/src/systemc/core/kernel.hh
index 9a81d9db4..8cbf4fb3b 100644
--- a/src/systemc/core/kernel.hh
+++ b/src/systemc/core/kernel.hh
@@ -48,6 +48,13 @@ class Kernel : public SimObject
   public:
     typedef SystemC_KernelParams Params;
     Kernel(Params *params);
+
+    void startup() override;
+
+    void t0Handler();
+
+  private:
+    EventWrapper<Kernel, &Kernel::t0Handler> t0Event;
 };
 
 } // namespace SystemC
diff --git a/src/systemc/core/list.hh b/src/systemc/core/list.hh
new file mode 100644
index 000000000..65eada27d
--- /dev/null
+++ b/src/systemc/core/list.hh
@@ -0,0 +1,113 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __SYSTEMC_CORE_LIST_HH__
+#define __SYSTEMC_CORE_LIST_HH__
+
+#include <functional>
+
+#include "base/fiber.hh"
+#include "systemc/core/object.hh"
+#include "systemc/ext/core/sc_event.hh"
+#include "systemc/ext/core/sc_module.hh"
+#include "systemc/ext/core/sc_process_handle.hh"
+
+namespace sc_gem5
+{
+
+struct ListNode
+{
+    ListNode() : nextListNode(nullptr), prevListNode(nullptr) {}
+    virtual ~ListNode() {}
+
+    ListNode *nextListNode;
+    ListNode *prevListNode;
+
+    void
+    popListNode()
+    {
+        if (nextListNode)
+            nextListNode->prevListNode = prevListNode;
+        if (prevListNode)
+            prevListNode->nextListNode = nextListNode;
+        nextListNode = nullptr;
+        prevListNode = nullptr;
+    }
+};
+
+template <typename T>
+struct NodeList : public ListNode
+{
+    NodeList()
+    {
+        nextListNode = this;
+        prevListNode = this;
+    }
+
+    void
+    pushFirst(T *t)
+    {
+        // Make sure this node isn't currently in a different list.
+        t->popListNode();
+
+        // The node behind t is whoever used to be first.
+        t->nextListNode = nextListNode;
+        // The node that used to be first is behind t.
+        nextListNode->prevListNode = t;
+
+        // Nobody is in front of t.
+        t->prevListNode = this;
+        // The first node is t.
+        nextListNode = t;
+    }
+
+    void
+    pushLast(T *t)
+    {
+        // Make sure this node isn't currently in a different list.
+        t->popListNode();
+
+        // The node in front of t is whoever used to be last.
+        t->prevListNode = prevListNode;
+        // The node that used to be last is in front of t.
+        prevListNode->nextListNode = t;
+
+        // Nobody is behind t.
+        t->nextListNode = this;
+        // The last node is t.
+        prevListNode = t;
+    }
+
+    T *getNext() { return dynamic_cast<T *>(nextListNode); }
+    bool empty() { return getNext() == nullptr; }
+};
+
+} // namespace sc_gem5
+
+#endif  //__SYSTEMC_CORE_LIST_HH__
diff --git a/src/systemc/core/object.cc b/src/systemc/core/object.cc
index cfd4c5e93..2bc6804e2 100644
--- a/src/systemc/core/object.cc
+++ b/src/systemc/core/object.cc
@@ -31,6 +31,7 @@
 
 #include "base/logging.hh"
 #include "systemc/core/module.hh"
+#include "systemc/core/scheduler.hh"
 
 namespace sc_gem5
 {
@@ -87,8 +88,9 @@ Object::Object(sc_core::sc_object *sc_obj, const char *obj_name) :
         // constructor is running.
         parent = p->obj()->sc_obj;
         addObject(&parent->_gem5_object->children, sc_obj);
-    } else if (false /* TODO Check if a process is running */) {
-        // The process is our parent.
+    } else if (scheduler.current()) {
+        // Our parent is the currently running process.
+        parent = scheduler.current();
     } else {
         // We're a top level object.
         addObject(&topLevelObjects, sc_obj);
diff --git a/src/systemc/core/process.cc b/src/systemc/core/process.cc
index 4597d8b60..26cfb7ecd 100644
--- a/src/systemc/core/process.cc
+++ b/src/systemc/core/process.cc
@@ -28,6 +28,7 @@
  */
 
 #include "systemc/core/process.hh"
+#include "systemc/core/scheduler.hh"
 
 namespace sc_gem5
 {
@@ -79,8 +80,9 @@ Process::suspend(bool inc_kids)
         //TODO Suspend this process.
     }
 
-    if (procKind() != ::sc_core::SC_METHOD_PROC_ /* && we're running */) {
-        // We suspended this thread or cthread. Stop running.
+    if (procKind() != ::sc_core::SC_METHOD_PROC_ &&
+            scheduler.current() == this) {
+        scheduler.yield();
     }
 }
 
@@ -189,16 +191,34 @@ Process::syncResetOff(bool inc_kids)
 }
 
 void
-Thread::throw_it(ExceptionWrapperBase &exc, bool inc_kids)
-{
-    Process::throw_it(exc, inc_kids);
-
-    if (_terminated)
-        return;
+Process::run()
+{
+    _running = true;
+    bool reset;
+    do {
+        reset = false;
+        try {
+            func->call();
+        } catch(::sc_core::sc_unwind_exception exc) {
+            reset = exc.is_reset();
+        }
+    } while (reset);
+    _running = false;
+}
 
-    injectException(exc);
+Process::Process(const char *name, ProcessFuncWrapper *func, bool _dynamic) :
+    ::sc_core::sc_object(name), excWrapper(nullptr), func(func),
+    _running(false), _dynamic(_dynamic), _isUnwinding(false),
+    _terminated(false), _suspended(false), _disabled(false),
+    _syncReset(false), refCount(0), stackSize(::Fiber::DefaultStackSize)
+{
+    _newest = this;
+    if (!_dynamic)
+        scheduler.init(this);
 }
 
+Process *Process::_newest;
+
 void
 throw_it_wrapper(Process *p, ExceptionWrapperBase &exc, bool inc_kids)
 {
diff --git a/src/systemc/core/process.hh b/src/systemc/core/process.hh
index 07ef97c5e..bb9a9c60c 100644
--- a/src/systemc/core/process.hh
+++ b/src/systemc/core/process.hh
@@ -33,6 +33,7 @@
 #include <functional>
 
 #include "base/fiber.hh"
+#include "systemc/core/list.hh"
 #include "systemc/core/object.hh"
 #include "systemc/ext/core/sc_event.hh"
 #include "systemc/ext/core/sc_module.hh"
@@ -41,10 +42,11 @@
 namespace sc_gem5
 {
 
-class Process : public ::sc_core::sc_object
+class Process : public ::sc_core::sc_object, public ListNode
 {
   public:
     virtual ::sc_core::sc_curr_proc_kind procKind() const = 0;
+    bool running() const { return _running; }
     bool dynamic() const { return _dynamic; }
     bool isUnwinding() const { return _isUnwinding; }
     bool terminated() const { return _terminated; }
@@ -75,12 +77,21 @@ class Process : public ::sc_core::sc_object
     const ::sc_core::sc_event &resetEvent() { return _resetEvent; }
     const ::sc_core::sc_event &terminatedEvent() { return _terminatedEvent; }
 
+    // This should only be called before initialization.
+    void dontInitialize() { popListNode(); }
+
+    void setStackSize(size_t size) { stackSize = size; }
+
+    void run();
+
+    virtual Fiber *fiber() { return Fiber::primaryFiber(); }
+
+    static Process *newest() { return _newest; }
+
   protected:
-    Process(const char *name, ProcessFuncWrapper *func, bool _dynamic) :
-        ::sc_core::sc_object(name), func(func), _dynamic(_dynamic),
-        _isUnwinding(false), _terminated(false), _suspended(false),
-        _disabled(false), _syncReset(false), refCount(0)
-    {}
+    Process(const char *name, ProcessFuncWrapper *func, bool _dynamic);
+
+    static Process *_newest;
 
     virtual ~Process() { delete func; }
 
@@ -89,6 +100,7 @@ class Process : public ::sc_core::sc_object
 
     ProcessFuncWrapper *func;
     sc_core::sc_curr_proc_kind _procKind;
+    bool _running;
     bool _dynamic;
     bool _isUnwinding;
     bool _terminated;
@@ -99,56 +111,8 @@ class Process : public ::sc_core::sc_object
     bool _syncReset;
 
     int refCount;
-};
-
-class Method : public Process
-{
-  public:
-    Method(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
-        Process(name, func, _dynamic)
-    {}
-
-    const char *kind() const override { return "sc_method_process"; }
-
-    sc_core::sc_curr_proc_kind
-    procKind() const override
-    {
-        return sc_core::SC_METHOD_PROC_;
-    }
-};
-
-class Thread : public Process
-{
-  public:
-    Thread(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
-        Process(name, func, _dynamic)
-    {}
-
-    const char *kind() const override { return "sc_thread_process"; }
-
-    void throw_it(ExceptionWrapperBase &exc, bool inc_kids) override;
-
-    sc_core::sc_curr_proc_kind
-    procKind() const override
-    {
-        return sc_core::SC_THREAD_PROC_;
-    }
-};
-
-class CThread : public Thread
-{
-  public:
-    CThread(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
-        Thread(name, func, _dynamic)
-    {}
-
-    const char *kind() const override { return "sc_cthread_process"; }
 
-    sc_core::sc_curr_proc_kind
-    procKind() const override
-    {
-        return sc_core::SC_CTHREAD_PROC_;
-    }
+    size_t stackSize;
 };
 
 } // namespace sc_gem5
diff --git a/src/systemc/core/process_types.cc b/src/systemc/core/process_types.cc
new file mode 100644
index 000000000..188225c02
--- /dev/null
+++ b/src/systemc/core/process_types.cc
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#include "systemc/core/process_types.hh"
+
+namespace sc_gem5
+{
+
+void
+Thread::throw_it(ExceptionWrapperBase &exc, bool inc_kids)
+{
+    Process::throw_it(exc, inc_kids);
+
+    if (_terminated)
+        return;
+
+    injectException(exc);
+}
+
+} // namespace sc_gem5
diff --git a/src/systemc/core/process_types.hh b/src/systemc/core/process_types.hh
new file mode 100644
index 000000000..6d13592b6
--- /dev/null
+++ b/src/systemc/core/process_types.hh
@@ -0,0 +1,118 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __SYSTEMC_CORE_PROCESS_TYPES_HH__
+#define __SYSTEMC_CORE_PROCESS_TYPES_HH__
+
+#include "systemc/core/process.hh"
+#include "systemc/core/scheduler.hh"
+
+namespace sc_gem5
+{
+
+class Method : public Process
+{
+  public:
+    Method(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
+        Process(name, func, _dynamic)
+    {}
+
+    const char *kind() const override { return "sc_method_process"; }
+
+    sc_core::sc_curr_proc_kind
+    procKind() const override
+    {
+        return sc_core::SC_METHOD_PROC_;
+    }
+};
+
+class Thread : public Process
+{
+  public:
+    Thread(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
+        Process(name, func, _dynamic), ctx(nullptr)
+    {}
+
+    ~Thread() { delete ctx; }
+
+    const char *kind() const override { return "sc_thread_process"; }
+
+    void throw_it(ExceptionWrapperBase &exc, bool inc_kids) override;
+
+    sc_core::sc_curr_proc_kind
+    procKind() const override
+    {
+        return sc_core::SC_THREAD_PROC_;
+    }
+
+    Fiber *
+    fiber() override
+    {
+        if (!ctx)
+            ctx = new Context(this, stackSize);
+        return ctx;
+    }
+
+  private:
+    class Context : public Fiber
+    {
+      public:
+        Context(Thread *thread, size_t size) : Fiber(size), thread(thread) {}
+
+      private:
+        Thread *thread;
+
+        void main() override { thread->run(); }
+    };
+
+    Context *ctx;
+};
+
+class CThread : public Thread
+{
+  public:
+    CThread(const char *name, ProcessFuncWrapper *func, bool _dynamic=false) :
+        Thread(name, func, _dynamic)
+    {
+        // We'll be in the initialization list now, but we shouldn't be.
+        popListNode();
+    }
+
+    const char *kind() const override { return "sc_cthread_process"; }
+
+    sc_core::sc_curr_proc_kind
+    procKind() const override
+    {
+        return sc_core::SC_CTHREAD_PROC_;
+    }
+};
+
+} // namespace sc_gem5
+
+#endif  //__SYSTEMC_CORE_PROCESS_TYPES_HH__
diff --git a/src/systemc/core/sc_module.cc b/src/systemc/core/sc_module.cc
index 44369d751..90139a166 100644
--- a/src/systemc/core/sc_module.cc
+++ b/src/systemc/core/sc_module.cc
@@ -32,7 +32,7 @@
 
 #include "base/logging.hh"
 #include "systemc/core/module.hh"
-#include "systemc/core/process.hh"
+#include "systemc/core/process_types.hh"
 #include "systemc/ext/core/sc_module.hh"
 #include "systemc/ext/core/sc_module_name.hh"
 
@@ -221,13 +221,13 @@ sc_module::async_reset_signal_is(const sc_signal_in_if<bool> &, bool)
 void
 sc_module::dont_initialize()
 {
-    warn("%s not implemented.\n", __PRETTY_FUNCTION__);
+    ::sc_gem5::Process::newest()->dontInitialize();
 }
 
 void
-sc_module::set_stack_size(size_t)
+sc_module::set_stack_size(size_t size)
 {
-    warn("%s not implemented.\n", __PRETTY_FUNCTION__);
+    ::sc_gem5::Process::newest()->setStackSize(size);
 }
 
 
diff --git a/src/systemc/core/sc_process_handle.cc b/src/systemc/core/sc_process_handle.cc
index eff2490ba..c4014b747 100644
--- a/src/systemc/core/sc_process_handle.cc
+++ b/src/systemc/core/sc_process_handle.cc
@@ -29,6 +29,7 @@
 
 #include "base/logging.hh"
 #include "systemc/core/process.hh"
+#include "systemc/core/scheduler.hh"
 #include "systemc/ext/core/sc_process_handle.hh"
 
 namespace sc_core
@@ -291,8 +292,7 @@ sc_process_handle::sync_reset_off(
 sc_process_handle
 sc_get_current_process_handle()
 {
-    warn("%s not implemented.\n", __PRETTY_FUNCTION__);
-    return sc_process_handle(nullptr /* Current process pointer */);
+    return sc_process_handle(::sc_gem5::scheduler.current());
 }
 
 bool
diff --git a/src/systemc/core/scheduler.cc b/src/systemc/core/scheduler.cc
new file mode 100644
index 000000000..41c64f876
--- /dev/null
+++ b/src/systemc/core/scheduler.cc
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#include "systemc/core/scheduler.hh"
+
+#include "base/fiber.hh"
+
+namespace sc_gem5
+{
+
+Scheduler::Scheduler() : _numCycles(0), _current(nullptr) {}
+
+void
+Scheduler::initialize()
+{
+    update();
+
+    while (!initList.empty())
+        ready(initList.getNext());
+
+    delta();
+}
+
+void
+Scheduler::runCycles()
+{
+    while (!readyList.empty()) {
+        evaluate();
+        update();
+        delta();
+    }
+}
+
+void
+Scheduler::yield()
+{
+    _current = readyList.getNext();
+    if (!_current) {
+        // There are no more processes, so return control to evaluate.
+        Fiber::primaryFiber()->run();
+    } else {
+        _current->popListNode();
+        // Switch to whatever Fiber is supposed to run this process. All
+        // Fibers which aren't running should be parked at this line.
+        _current->fiber()->run();
+        // If the current process hasn't been started yet, start it. This
+        // should always be true for methods, but may not be true for threads.
+        if (_current && !_current->running())
+            _current->run();
+    }
+}
+
+void
+Scheduler::evaluate()
+{
+    if (!readyList.empty())
+        _numCycles++;
+
+    do {
+        yield();
+    } while (!readyList.empty());
+}
+
+void
+Scheduler::update()
+{
+}
+
+void
+Scheduler::delta()
+{
+}
+
+Scheduler scheduler;
+
+} // namespace sc_gem5
diff --git a/src/systemc/core/scheduler.hh b/src/systemc/core/scheduler.hh
new file mode 100644
index 000000000..a7216231a
--- /dev/null
+++ b/src/systemc/core/scheduler.hh
@@ -0,0 +1,101 @@
+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Gabe Black
+ */
+
+#ifndef __SYSTEMC_CORE_SCHEDULER_HH__
+#define __SYSTEMC_CORE_SCHEDULER_HH__
+
+#include "systemc/core/list.hh"
+#include "systemc/core/process.hh"
+
+namespace sc_gem5
+{
+
+typedef NodeList<Process> ProcessList;
+
+class Scheduler
+{
+  public:
+    Scheduler();
+
+    uint64_t numCycles() { return _numCycles; }
+    Process *current() { return _current; }
+
+    // Run the initialization phase.
+    void initialize();
+
+    // Run delta cycles until time needs to advance.
+    void runCycles();
+
+    // Put a process on the list of processes to be initialized.
+    void init(Process *p) { initList.pushLast(p); }
+
+    // Run the next process, if there is one.
+    void yield();
+
+    // Put a process on the ready list.
+    void
+    ready(Process *p)
+    {
+        // Clump methods together to minimize context switching.
+        if (p->procKind() == ::sc_core::SC_METHOD_PROC_)
+            readyList.pushFirst(p);
+        else
+            readyList.pushLast(p);
+    }
+
+    // Run the given process immediately, preempting whatever may be running.
+    void
+    runNow(Process *p)
+    {
+        // If a process is running, schedule it/us to run again.
+        if (_current)
+            readyList.pushFirst(_current);
+        // Schedule p to run first.
+        readyList.pushFirst(p);
+        yield();
+    }
+
+  private:
+    uint64_t _numCycles;
+
+    Process *_current;
+
+    ProcessList initList;
+    ProcessList readyList;
+
+    void evaluate();
+    void update();
+    void delta();
+};
+
+extern Scheduler scheduler;
+
+} // namespace sc_gem5
+
+#endif // __SYSTEMC_CORE_SCHEDULER_H__