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>

4 files changed, 29 insertions, 3 deletions

diff --git a/src/systemc/core/sc_prim.cc b/src/systemc/core/sc_prim.cc
index 91befa836..170abb541 100644
--- a/src/systemc/core/sc_prim.cc
+++ b/src/systemc/core/sc_prim.cc
@@ -29,8 +29,16 @@
 
 #include "base/logging.hh"
 #include "systemc/core/channel.hh"
+#include "systemc/core/scheduler.hh"
 #include "systemc/ext/core/sc_prim.hh"
 
+namespace sc_gem5
+{
+
+uint64_t getChangeStamp() { return scheduler.changeStamp(); }
+
+} // namespace sc_gem5
+
 namespace sc_core
 {
 
diff --git a/src/systemc/core/scheduler.cc b/src/systemc/core/scheduler.cc
index 9b431acba..e2d8e62f4 100644
--- a/src/systemc/core/scheduler.cc
+++ b/src/systemc/core/scheduler.cc
@@ -46,7 +46,7 @@ Scheduler::Scheduler() :
     starvationEvent(this, false, StarvationPriority),
     _started(false), _paused(false), _stopped(false),
     maxTickEvent(this, false, MaxTickPriority),
-    _numCycles(0), _current(nullptr), initDone(false),
+    _numCycles(0), _changeStamp(0), _current(nullptr), initDone(false),
     runOnce(false)
 {}
 
@@ -265,14 +265,17 @@ void
 Scheduler::runReady()
 {
     bool empty = readyList.empty();
+    lastReadyTick = getCurTick();
 
     // The evaluation phase.
     do {
         yield();
     } while (!readyList.empty());
 
-    if (!empty)
+    if (!empty) {
         _numCycles++;
+        _changeStamp++;
+    }
 
     // The update phase.
     update();
@@ -334,6 +337,7 @@ Scheduler::start(Tick max_tick, bool run_to_time)
     runToTime = run_to_time;
 
     maxTick = max_tick;
+    lastReadyTick = getCurTick();
 
     if (initDone) {
         if (!runToTime && starved())
diff --git a/src/systemc/core/scheduler.hh b/src/systemc/core/scheduler.hh
index f55ff1f83..2bee0b090 100644
--- a/src/systemc/core/scheduler.hh
+++ b/src/systemc/core/scheduler.hh
@@ -275,6 +275,7 @@ class Scheduler
     void
     completeTimeSlot(TimeSlot *ts)
     {
+        _changeStamp++;
         assert(ts == timeSlots.begin()->second);
         timeSlots.erase(timeSlots.begin());
         if (!runToTime && starved())
@@ -327,6 +328,8 @@ class Scheduler
     bool paused() { return _paused; }
     bool stopped() { return _stopped; }
 
+    uint64_t changeStamp() { return _changeStamp; }
+
   private:
     typedef const EventBase::Priority Priority;
     static Priority DefaultPriority = EventBase::Default_Pri;
@@ -388,9 +391,18 @@ class Scheduler
     bool _stopped;
 
     Tick maxTick;
-    EventWrapper<Scheduler, &Scheduler::pause> maxTickEvent;
+    Tick lastReadyTick;
+    void
+    maxTickFunc()
+    {
+        if (lastReadyTick != getCurTick())
+            _changeStamp++;
+        pause();
+    }
+    EventWrapper<Scheduler, &Scheduler::maxTickFunc> maxTickEvent;
 
     uint64_t _numCycles;
+    uint64_t _changeStamp;
 
     Process *_current;
 
diff --git a/src/systemc/ext/core/sc_prim.hh b/src/systemc/ext/core/sc_prim.hh
index 99e231456..73b8784a6 100644
--- a/src/systemc/ext/core/sc_prim.hh
+++ b/src/systemc/ext/core/sc_prim.hh
@@ -38,6 +38,8 @@ namespace sc_gem5
 
 class Channel;
 
+uint64_t getChangeStamp();
+
 } // namespace sc_gem5
 
 namespace sc_core