Initial version

code/machine/timer.cc

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+// timer.cc 
+//	Routines to emulate a hardware timer device.
+//
+//      A hardware timer generates a CPU interrupt every X milliseconds.
+//      This means it can be used for implementing time-slicing.
+//
+//      We emulate a hardware timer by scheduling an interrupt to occur
+//      every time stats->totalTicks has increased by TimerTicks.
+//
+//      In order to introduce some randomness into time-slicing, if "doRandom"
+//      is set, then the interrupt is comes after a random number of ticks.
+//
+//	Remember -- nothing in here is part of Nachos.  It is just
+//	an emulation for the hardware that Nachos is running on top of.
+//
+//  DO NOT CHANGE -- part of the machine emulation
+//
+// Copyright (c) 1992-1993 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+
+#include "copyright.h"
+#include "timer.h"
+#include "system.h"
+
+// dummy function because C++ does not allow pointers to member functions
+static void TimerHandler(void *arg)
+{ Timer *p = (Timer *)arg; p->TimerExpired(); }
+
+//----------------------------------------------------------------------
+// Timer::Timer
+//      Initialize a hardware timer device.  Save the place to call
+//	on each interrupt, and then arrange for the timer to start
+//	generating interrupts.
+//
+//      "timerHandler" is the interrupt handler for the timer device.
+//		It is called with interrupts disabled every time the
+//		the timer expires.
+//      "callArg" is the parameter to be passed to the interrupt handler.
+//      "doRandom" -- if true, arrange for the interrupts to occur
+//		at random, instead of fixed, intervals.
+//----------------------------------------------------------------------
+
+Timer::Timer(VoidFunctionPtr timerHandler, void *callArg, bool doRandom)
+{
+    randomize = doRandom;
+    handler = timerHandler;
+    arg = callArg; 
+
+    // schedule the first interrupt from the timer device
+    interrupt->Schedule(TimerHandler, this, TimeOfNextInterrupt(), 
+		TimerInt); 
+}
+
+//----------------------------------------------------------------------
+// Timer::TimerExpired
+//      Routine to simulate the interrupt generated by the hardware 
+//	timer device.  Schedule the next interrupt, and invoke the
+//	interrupt handler.
+//----------------------------------------------------------------------
+void 
+Timer::TimerExpired() 
+{
+    // schedule the next timer device interrupt
+    interrupt->Schedule(TimerHandler, this, TimeOfNextInterrupt(), 
+		TimerInt);
+
+    // invoke the Nachos interrupt handler for this device
+    (*handler)(arg);
+}
+
+//----------------------------------------------------------------------
+// Timer::TimeOfNextInterrupt
+//      Return when the hardware timer device will next cause an interrupt.
+//	If randomize is turned on, make it a (pseudo-)random delay.
+//----------------------------------------------------------------------
+
+int 
+Timer::TimeOfNextInterrupt() 
+{
+    if (randomize)
+	return 1 + (Random() % (TimerTicks * 2));
+    else
+	return TimerTicks; 
+}