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