translate.h

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// translate.h 
//      Data structures for managing the translation from 
//      virtual page # -> physical page #, used for managing
//      physical memory on behalf of user programs.
//
//      The data structures in this file are "dual-use" - they
//      serve both as a page table entry, and as an entry in
//      a software-managed translation lookaside buffer (TLB).
//      Either way, each entry is of the form:
//      <virtual page #, physical page #>.
//
// 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.

#ifndef TLB_H
#define TLB_H

#include "copyright.h"
#include "utility.h"

// The following class defines an entry in a translation table -- either
// in a page table or a TLB.  Each entry defines a mapping from one 
// virtual page to one physical page.
// In addition, there are some extra bits for access control (valid and 
// read-only) and some bits for usage information (use and dirty).

class TranslationEntry {
  public:
    int virtualPage;    // The page number in virtual memory.
    int physicalPage;   // The page number in real memory (relative to the
                        //  start of "mainMemory"
    bool valid;         // If this bit is set, the translation is ignored.
                        // (In other words, the entry hasn't been initialized.)
    bool readOnly;      // If this bit is set, the user program is not allowed
                        // to modify the contents of the page.
    bool use;           // This bit is set by the hardware every time the
                        // page is referenced or modified.
    bool dirty;         // This bit is set by the hardware every time the
                        // page is modified.
};

#endif

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