// machine.cc //	Routines for simulating the execution of user programs.////  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.#include "copyright.h"#include "machine.h"#include "system.h"// Textual names of the exceptions that can be generated by user program// execution, for debugging.static char* exceptionNames[] = { "no exception", "syscall", 				"page fault/no TLB entry", "page read only",				"bus error", "address error", "overflow",				"illegal instruction" };//----------------------------------------------------------------------// CheckEndian// 	Check to be sure that the host really uses the format it says it //	does, for storing the bytes of an integer.  Stop on error.//----------------------------------------------------------------------staticvoid CheckEndian(){    union checkit {        char charword[4];        unsigned int intword;    } check;    check.charword[0] = 1;    check.charword[1] = 2;    check.charword[2] = 3;    check.charword[3] = 4;#ifdef HOST_IS_BIG_ENDIAN    ASSERT (check.intword == 0x01020304);#else    ASSERT (check.intword == 0x04030201);#endif}//----------------------------------------------------------------------// Machine::Machine// 	Initialize the simulation of user program execution.////	"debug" -- if TRUE, drop into the debugger after each user instruction//		is executed.//----------------------------------------------------------------------Machine::Machine(bool debug){    int i;    for (i = 0; i < NumTotalRegs; i++)        registers[i] = 0;    mainMemory = new char[MemorySize];    for (i = 0; i < MemorySize; i++)      	mainMemory[i] = 0;#ifdef USE_TLB    tlb = new TranslationEntry[TLBSize];    for (i = 0; i < TLBSize; i++)	tlb[i].valid = FALSE;    pageTable = NULL;#else	// use linear page table    tlb = NULL;    pageTable = NULL;#endif    singleStep = debug;    CheckEndian();}//----------------------------------------------------------------------// Machine::~Machine// 	De-allocate the data structures used to simulate user program execution.//----------------------------------------------------------------------Machine::~Machine(){    delete [] mainMemory;    if (tlb != NULL)        delete [] tlb;}//----------------------------------------------------------------------// Machine::RaiseException// 	Transfer control to the Nachos kernel from user mode, because//	the user program either invoked a system call, or some exception//	occured (such as the address translation failed).////	"which" -- the cause of the kernel trap//	"badVaddr" -- the virtual address causing the trap, if appropriate//----------------------------------------------------------------------voidMachine::RaiseException(ExceptionType which, int badVAddr){    DEBUG('m', "Exception: %s\n", exceptionNames[which]);    //  ASSERT(interrupt->getStatus() == UserMode);    registers[BadVAddrReg] = badVAddr;    DelayedLoad(0, 0);			// finish anything in progress    interrupt->setStatus(SystemMode);    ExceptionHandler(which);		// interrupts are enabled at this point    interrupt->setStatus(UserMode);}//----------------------------------------------------------------------// Machine::Debugger// 	Primitive debugger for user programs.  Note that we can't use//	gdb to debug user programs, since gdb doesn't run on top of Nachos.//	It could, but you'd have to implement *a lot* more system calls//	to get it to work!////	So just allow single-stepping, and printing the contents of memory.//----------------------------------------------------------------------void Machine::Debugger(){    char *buf = new char[80];    int num;    interrupt->DumpState();    DumpState();    printf("%d> ", stats->totalTicks);    fflush(stdout);    fgets(buf, 80, stdin);    if (sscanf(buf, "%d", &num) == 1)	runUntilTime = num;    else {	runUntilTime = 0;	switch (*buf) {	  case '\n':	    break;	    	  case 'c':	    singleStep = FALSE;	    break;	    	  case '?':	    printf("Machine commands:\n");	    printf("    <return>  execute one instruction\n");	    printf("    <number>  run until the given timer tick\n");	    printf("    c         run until completion\n");	    printf("    ?         print help message\n");	    break;	}    }    delete [] buf;} //----------------------------------------------------------------------// Machine::DumpState// 	Print the user program's CPU state.  We might print the contents//	of memory, but that seemed like overkill.//----------------------------------------------------------------------voidMachine::DumpState(){    int i;        printf("Machine registers:\n");    for (i = 0; i < NumGPRegs; i++)	switch (i) {	  case StackReg:	    printf("\tSP(%d):\t0x%x%s", i, registers[i],		   ((i % 4) == 3) ? "\n" : "");	    break;	    	  case RetAddrReg:	    printf("\tRA(%d):\t0x%x%s", i, registers[i],		   ((i % 4) == 3) ? "\n" : "");	    break;	  	  default:	    printf("\t%d:\t0x%x%s", i, registers[i],		   ((i % 4) == 3) ? "\n" : "");	    break;	}        printf("\tHi:\t0x%x", registers[HiReg]);    printf("\tLo:\t0x%x\n", registers[LoReg]);    printf("\tPC:\t0x%x", registers[PCReg]);    printf("\tNextPC:\t0x%x", registers[NextPCReg]);    printf("\tPrevPC:\t0x%x\n", registers[PrevPCReg]);    printf("\tLoad:\t0x%x", registers[LoadReg]);    printf("\tLoadV:\t0x%x\n", registers[LoadValueReg]);    printf("\n");}//----------------------------------------------------------------------// Machine::ReadRegister/WriteRegister//   	Fetch or write the contents of a user program register.//----------------------------------------------------------------------int Machine::ReadRegister(int num)    {	ASSERT((num >= 0) && (num < NumTotalRegs));	return registers[num];    }void Machine::WriteRegister(int num, int value)    {	ASSERT((num >= 0) && (num < NumTotalRegs));	// DEBUG('m', "WriteRegister %d, value %d\n", num, value);	registers[num] = value;    }