sim: separate nextCycle() and clockEdge() in clockedObjects

Previously, nextCycle() could return the *current* cycle if the current tick was
already aligned with the clock edge. This behavior is not only confusing (not
quite what the function name implies), but also caused problems in the
drainResume() function. When exiting/re-entering the sim loop (e.g., to take
checkpoints), the CPUs will drain and resume. Due to the previous behavior of
nextCycle(), the CPU tick events were being rescheduled in the same ticks that
were already processed before draining. This caused divergence from runs that
did not exit/re-entered the sim loop. (Initially a cycle difference, but a
significant impact later on.)

This patch separates out the two behaviors (nextCycle() and clockEdge()),
uses nextCycle() in drainResume, and uses clockEdge() everywhere else.
Nothing (other than name) should change except for the drainResume timing.

1 files changed, 4 insertions, 4 deletions

diff --git a/src/dev/arm/hdlcd.cc b/src/dev/arm/hdlcd.cc
index 14128c730..c5daebc9b 100644
--- a/src/dev/arm/hdlcd.cc
+++ b/src/dev/arm/hdlcd.cc
@@ -282,7 +282,7 @@ HDLcd::write(PacketPtr pkt)
             if (new_command.enable) {
                 doUpdateParams = true;
                 if (!frameUnderway) {
-                    schedule(startFrameEvent, nextCycle());
+                    schedule(startFrameEvent, clockEdge());
                 }
             }
         }
@@ -514,7 +514,7 @@ HDLcd::renderPixel()
             frameUnderrun = true;
             int_rawstat.underrun = 1;
             if (!intEvent.scheduled())
-                schedule(intEvent, nextCycle());
+                schedule(intEvent, clockEdge());
         } else {
             // emulate the pixel read from the internal buffer
             pixelBufferSize -= bytesPerPixel() * count;
@@ -524,7 +524,7 @@ HDLcd::renderPixel()
     // the DMA may have previously stalled due to the buffer being full;
     //   give it a kick; it knows not to fill if at end of frame, underrun, etc
     if (!fillPixelBufferEvent.scheduled())
-        schedule(fillPixelBufferEvent, nextCycle());
+        schedule(fillPixelBufferEvent, clockEdge());
 
     // schedule the next pixel read according to where it is in the frame
     pixelIndex += count;
@@ -597,7 +597,7 @@ HDLcd::dmaDone(DmaDoneEvent *event)
     if ((dmaCurAddr < dmaMaxAddr) &&
         (bytesFreeInPixelBuffer() + targetTransSize < PIXEL_BUFFER_CAPACITY) &&
         !fillPixelBufferEvent.scheduled()) {
-        schedule(fillPixelBufferEvent, nextCycle());
+        schedule(fillPixelBufferEvent, clockEdge());
     }
 }