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PendingInterrupt CRC

Name:

 PendingInterrupt

Comment:

 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).

Collaborators:

 
// 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.

Responsibilities: 

class PendingInterrupt {
  public:
    PendingInterrupt(VoidFunctionPtr func, int param, int time, IntType kind);
                                // initialize an interrupt that will
                                // occur in the future

    VoidFunctionPtr handler;    // The function (in the hardware device
                                // emulator) to call when the interrupt occurs
    int arg;                    // The argument to the function.
    int when;                   // When the interrupt is supposed to fire
    IntType type;               // for debugging
};