oneshot.cpp

LINUX 下的 NACHOS 系统 实现系统调度的算法功能

// oneshot.cc 
//  Routines to emulate a hardware one-shot timer device.
//
//      A one-shot hardware timer generates a CPU interrupt in X milliseconds.
//      The interrupt will only occur once and not ever X milliseconds.
//      This means it can be used for implementing time-slicing.
//
//  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
//
//
//  Adapted from NachOS' timer.cc.
//

#include "copyright.h"
#include "oneshot.h"
#include "system.h"

//----------------------------------------------------------------------
// OneShotHandler
//      The actual function to handle the interrupt. Used because of
//  problems with C++ and function pointers.
//
//      "arg" is the parameter passed to the user specified handler.
//----------------------------------------------------------------------

static void OneShotHandler(int arg)
{
  OneShot *p = (OneShot *)arg;
  p->TimerExpired();
}

//----------------------------------------------------------------------
// OneShot::OneShot
//      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.
//      "time" is the number of milliseconds until the interrupt
//             should occur
//----------------------------------------------------------------------
OneShot::OneShot()
{ 
}

void OneShot::SetArg(VoidFunctionPtr timerHandler, int callArg, int time)
{
  handler = timerHandler;
  arg = callArg; 

  // schedule interrupt for the one shot timer device
  interrupt->Schedule(OneShotHandler, (int)this, time, TimerInt); 
  // the above code makes a bad assumption that a pointer is the same
  // size as an int.
}


OneShot::OneShot(VoidFunctionPtr timerHandler, int callArg, int time)
{
  handler = timerHandler;
  arg = callArg; 

  // schedule interrupt for the one shot timer device
  interrupt->Schedule(OneShotHandler, (int)this, time, TimerInt); 
  // the above code makes a bad assumption that a pointer is the same
  // size as an int.
}

//----------------------------------------------------------------------
// OneShot::TimerExpired
//      Routine to simulate the interrupt generated by the hardware 
//  timer device.  Invoke the interrupt handler.
//----------------------------------------------------------------------
void OneShot::TimerExpired() 
{
  // invoke the Nachos interrupt handler for this device
  (*handler)(arg);
}