interrupt.h

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// interrupt.h 
//      Data structures to emulate low-level interrupt hardware.
//
//      The hardware provides a routine (SetLevel) to enable or disable
//      interrupts.
//
//      In order to emulate the hardware, we need to keep track of all
//      interrupts the hardware devices would cause, and when they
//      are supposed to occur.  
//
//      This module also keeps track of simulated time.  Time advances
//      only when the following occur: 
//              interrupts are re-enabled
//              a user instruction is executed
//              there is nothing in the ready queue
//
//      As a result, unlike real hardware, interrupts (and thus time-slice 
//      context switches) cannot occur anywhere in the code where interrupts
//      are enabled, but rather only at those places in the code where 
//      simulated time advances (so that it becomes time to invoke an
//      interrupt in the hardware simulation).
//
//      NOTE: this means that incorrectly synchronized code may work
//      fine on this hardware simulation (even with randomized time slices),
//      but it wouldn't work on real hardware.
//
//  DO NOT CHANGE -- part of the machine emulation
//
// Copyright (c) 1992-1996 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.

#ifndef INTERRUPT_H
#define INTERRUPT_H

#include "copyright.h"
#include "list.h"
#include "callback.h"

// Interrupts can be disabled (IntOff) or enabled (IntOn)
enum IntStatus { IntOff, IntOn };

// Nachos can be running kernel code (SystemMode), user code (UserMode),
// or there can be no runnable thread, because the ready list 
// is empty (IdleMode).
enum MachineStatus {IdleMode, SystemMode, UserMode};

// IntType records which hardware device generated an interrupt.
// In Nachos, we support a hardware timer device, a disk, a console
// display and keyboard, and a network.
enum IntType { TimerInt, DiskInt, ConsoleWriteInt, ConsoleReadInt, 
                        NetworkSendInt, NetworkRecvInt};

// The following class defines an interrupt that is scheduled
// to occur in the future.  The internal data structures are
// left public to make it simpler to manipulate.

class PendingInterrupt {
  public:
    PendingInterrupt(CallBackObj *callOnInt, int time, IntType kind);
                                // initialize an interrupt that will
                                // occur in the future

    CallBackObj *callOnInterrupt;// The object (in the hardware device
                                // emulator) to call when the interrupt occurs
    
    int when;                   // When the interrupt is supposed to fire
    IntType type;               // for debugging
};

// The following class defines the data structures for the simulation
// of hardware interrupts.  We record whether interrupts are enabled
// or disabled, and any hardware interrupts that are scheduled to occur
// in the future.

class Interrupt {
  public:
    Interrupt();                // initialize the interrupt simulation
    ~Interrupt();               // de-allocate data structures
    
    IntStatus SetLevel(IntStatus level);
                                // Disable or enable interrupts 
                                // and return previous setting.

    void Enable() { (void) SetLevel(IntOn); }
                                // Enable interrupts.
    IntStatus getLevel() {return level;}
                                // Return whether interrupts
                                // are enabled or disabled
    
    void Idle();                // The ready queue is empty, roll 
                                // simulated time forward until the 
                                // next interrupt

    void Halt();                // quit and print out stats
    
    void YieldOnReturn();       // cause a context switch on return 
                                // from an interrupt handler

    MachineStatus getStatus() { return status; } 
    void setStatus(MachineStatus st) { status = st; }
                                // idle, kernel, user

    void DumpState();           // Print interrupt state
    

    // NOTE: the following are internal to the hardware simulation code.
    // DO NOT call these directly.  I should make them "private",
    // but they need to be public since they are called by the
    // hardware device simulators.

    void Schedule(CallBackObj *callTo, int when, IntType type);
                                // Schedule an interrupt to occur
                                // at time "when".  This is called
                                // by the hardware device simulators.
    
    void OneTick();             // Advance simulated time

  private:
    IntStatus level;            // are interrupts enabled or disabled?
    SortedList<PendingInterrupt *> *pending;            
                                // the list of interrupts scheduled
                                // to occur in the future
    bool inHandler;             // TRUE if we are running an interrupt handler
    bool yieldOnReturn;         // TRUE if we are to context switch
                                // on return from the interrupt handler
    MachineStatus status;       // idle, kernel mode, user mode

    // these functions are internal to the interrupt simulation code

    bool CheckIfDue(bool advanceClock); 
                                // Check if any interrupts are supposed
                                // to occur now, and if so, do them

    void ChangeLevel(IntStatus old,     // SetLevel, without advancing the
                        IntStatus now); // simulated time
};

#endif // INTERRRUPT_H

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