Clock: Add a Cycles wrapper class and use where applicable

This patch addresses the comments and feedback on the preceding patch
that reworks the clocks and now more clearly shows where cycles
(relative cycle counts) are used to express time.

Instead of bumping the existing patch I chose to make this a separate
patch, merely to try and focus the discussion around a smaller set of
changes. The two patches will be pushed together though.

This changes done as part of this patch are mostly following directly
from the introduction of the wrapper class, and change enough code to
make things compile and run again. There are definitely more places
where int/uint/Tick is still used to represent cycles, and it will
take some time to chase them all down. Similarly, a lot of parameters
should be changed from Param.Tick and Param.Unsigned to
Param.Cycles.

In addition, the use of curTick is questionable as there should not be
an absolute cycle. Potential solutions can be built on top of this
patch. There is a similar situation in the o3 CPU where
lastRunningCycle is currently counting in Cycles, and is still an
absolute time. More discussion to be had in other words.

An additional change that would be appropriate in the future is to
perform a similar wrapping of Tick and probably also introduce a
Ticks class along with suitable operators for all these classes.

3 files changed, 11 insertions, 12 deletions

diff --git a/src/sim/clocked_object.hh b/src/sim/clocked_object.hh
index 050a15a74..78539c9c9 100644
--- a/src/sim/clocked_object.hh
+++ b/src/sim/clocked_object.hh
@@ -64,7 +64,7 @@ class ClockedObject : public SimObject
 
     // The cycle counter value corresponding to the current value of
     // 'tick'
-    mutable Tick cycle;
+    mutable Cycles cycle;
 
     /**
      * Prevent inadvertent use of the copy constructor and assignment
@@ -96,7 +96,7 @@ class ClockedObject : public SimObject
         // if not, we have to recalculate the cycle and tick, we
         // perform the calculations in terms of relative cycles to
         // allow changes to the clock period in the future
-        Tick elapsedCycles = divCeil(curTick() - tick, clock);
+        Cycles elapsedCycles(divCeil(curTick() - tick, clock));
         cycle += elapsedCycles;
         tick += elapsedCycles * clock;
     }
@@ -130,22 +130,22 @@ class ClockedObject : public SimObject
      *
      * @return The tick when the clock edge occurs
      */
-    inline Tick clockEdge(int cycles = 0) const
+    inline Tick clockEdge(Cycles cycles = Cycles(0)) const
     {
         // align tick to the next clock edge
         update();
 
         // figure out when this future cycle is
-        return tick + ticks(cycles);
+        return tick + clock * cycles;
     }
 
     /**
      * Determine the current cycle, corresponding to a tick aligned to
      * a clock edge.
      *
-     * @return The current cycle
+     * @return The current cycle count
      */
-    inline Tick curCycle() const
+    inline Cycles curCycle() const
     {
         // align cycle to the next clock edge.
         update();
@@ -162,13 +162,12 @@ class ClockedObject : public SimObject
     Tick nextCycle() const
     { return clockEdge(); }
 
-    inline Tick frequency() const { return SimClock::Frequency / clock; }
-
-    inline Tick ticks(int cycles) const { return clock * cycles; }
+    inline uint64_t frequency() const { return SimClock::Frequency / clock; }
 
     inline Tick clockPeriod() const { return clock; }
 
-    inline Tick tickToCycle(Tick tick) const { return tick / clock; }
+    inline Cycles ticksToCycles(Tick tick) const
+    { return Cycles(tick / clock); }
 
 };
 
diff --git a/src/sim/process.cc b/src/sim/process.cc
index f92fb91e2..08636b2c4 100644
--- a/src/sim/process.cc
+++ b/src/sim/process.cc
@@ -245,7 +245,7 @@ Process::initState()
     ThreadContext *tc = system->getThreadContext(contextIds[0]);
 
     // mark this context as active so it will start ticking.
-    tc->activate(0);
+    tc->activate(Cycles(0));
 }
 
 // map simulator fd sim_fd to target fd tgt_fd
diff --git a/src/sim/pseudo_inst.cc b/src/sim/pseudo_inst.cc
index 8a7f0c469..aafa5672b 100644
--- a/src/sim/pseudo_inst.cc
+++ b/src/sim/pseudo_inst.cc
@@ -172,7 +172,7 @@ quiesceCycles(ThreadContext *tc, uint64_t cycles)
 
     EndQuiesceEvent *quiesceEvent = tc->getQuiesceEvent();
 
-    Tick resume = curTick() + cpu->ticks(cycles);
+    Tick resume = cpu->clockEdge(Cycles(cycles));
 
     cpu->reschedule(quiesceEvent, resume, true);