Clock: Rework clocks to avoid tick-to-cycle transformations

This patch introduces the notion of a clock update function that aims
to avoid costly divisions when turning the current tick into a
cycle. Each clocked object advances a private (hidden) cycle member
and a tick member and uses these to implement functions for getting
the tick of the next cycle, or the tick of a cycle some time in the
future.

In the different modules using the clocks, changes are made to avoid
counting in ticks only to later translate to cycles. There are a few
oddities in how the O3 and inorder CPU count idle cycles, as seen by a
few locations where a cycle is subtracted in the calculation. This is
done such that the regression does not change any stats, but should be
revisited in a future patch.

Another, much needed, change that is not done as part of this patch is
to introduce a new typedef uint64_t Cycle to be able to at least hint
at the unit of the variables counting Ticks vs Cycles. This will be
done as a follow-up patch.

As an additional follow up, the thread context still uses ticks for
the book keeping of last activate and last suspend and this should
probably also be changed into cycles as well.

3 files changed, 14 insertions, 12 deletions

diff --git a/src/dev/arm/pl111.cc b/src/dev/arm/pl111.cc
index d79a1cf39..7990e02ed 100644
--- a/src/dev/arm/pl111.cc
+++ b/src/dev/arm/pl111.cc
@@ -440,7 +440,7 @@ Pl111::readFramebuffer()
         schedule(intEvent, nextCycle());
 
     curAddr = 0;
-    startTime = curTick();
+    startTime = curCycle();
 
     maxAddr = static_cast<Addr>(length * bytesPerPixel);
 
@@ -475,12 +475,12 @@ Pl111::fillFifo()
 void
 Pl111::dmaDone()
 {
-    Tick maxFrameTime = lcdTiming2.cpl * height * clock;
+    Tick maxFrameTime = lcdTiming2.cpl * height;
 
     --dmaPendingNum;
 
     if (maxAddr == curAddr && !dmaPendingNum) {
-        if ((curTick() - startTime) > maxFrameTime) {
+        if ((curCycle() - startTime) > maxFrameTime) {
             warn("CLCD controller buffer underrun, took %d cycles when should"
                  " have taken %d\n", curTick() - startTime, maxFrameTime);
             lcdRis.underflow = 1;
@@ -498,11 +498,13 @@ Pl111::dmaDone()
         pic->seekp(0);
         bmp->write(pic);
 
-        DPRINTF(PL111, "-- schedule next dma read event at %d tick \n",
-                maxFrameTime + curTick());
-
+        // schedule the next read based on when the last frame started
+        // and the desired fps (i.e. maxFrameTime), we turn the
+        // argument into a relative number of cycles in the future by
+        // subtracting curCycle()
         if (lcdControl.lcden)
-            schedule(readEvent, nextCycle(startTime + maxFrameTime));
+            schedule(readEvent, clockEdge(startTime + maxFrameTime -
+                                          curCycle()));
     }
 
     if (dmaPendingNum > (maxOutstandingDma - waterMark))
diff --git a/src/dev/i8254xGBe.cc b/src/dev/i8254xGBe.cc
index f7f6a1178..3ba140bce 100644
--- a/src/dev/i8254xGBe.cc
+++ b/src/dev/i8254xGBe.cc
@@ -2052,7 +2052,7 @@ IGbE::restartClock()
 {
     if (!tickEvent.scheduled() && (rxTick || txTick || txFifoTick) &&
         getState() == SimObject::Running)
-        schedule(tickEvent, (curTick() / ticks(1)) * ticks(1) + ticks(1));
+        schedule(tickEvent, clockEdge(1));
 }
 
 unsigned int
@@ -2434,7 +2434,7 @@ IGbE::tick()
 
 
     if (rxTick || txTick || txFifoTick)
-        schedule(tickEvent, curTick() + ticks(1));
+        schedule(tickEvent, curTick() + clockPeriod());
 }
 
 void
diff --git a/src/dev/ns_gige.cc b/src/dev/ns_gige.cc
index 6a55516c5..583cdb140 100644
--- a/src/dev/ns_gige.cc
+++ b/src/dev/ns_gige.cc
@@ -1147,7 +1147,7 @@ NSGigE::rxKick()
         }
 
         // Go to the next state machine clock tick.
-        rxKickTick = curTick() + ticks(1);
+        rxKickTick = curTick() + clockPeriod();
     }
 
     switch(rxDmaState) {
@@ -1594,7 +1594,7 @@ NSGigE::txKick()
         }
 
         // Go to the next state machine clock tick.
-        txKickTick = curTick() + ticks(1);
+        txKickTick = curTick() + clockPeriod();
     }
 
     switch(txDmaState) {
@@ -2015,7 +2015,7 @@ NSGigE::transferDone()
 
     DPRINTF(Ethernet, "transfer complete: data in txFifo...schedule xmit\n");
 
-    reschedule(txEvent, curTick() + ticks(1), true);
+    reschedule(txEvent, curTick() + clockPeriod(), true);
 }
 
 bool