diff --git a/code/build.linux/Makefile b/code/build.linux/Makefile
index 54fcf99..544a062 100644
--- a/code/build.linux/Makefile
+++ b/code/build.linux/Makefile
@@ -200,18 +200,18 @@ DEFINES =  -DFILESYS_STUB -DRDATA -DSIM_FIX
 # break the thread system.  You might want to use -fno-inline if
 # you need to call some inline functions from the debugger.
 
-CFLAGS = -g -Wall -Wextra $(INCPATH) $(DEFINES) $(HOSTCFLAGS) -DCHANGED -m32 # -fsanitize=address,undefined
-LDFLAGS = -m32 # -fsanitize=address,undefined
+CFLAGS = -g -Wall $(INCPATH) $(DEFINES) $(HOSTCFLAGS) -DCHANGED -m32 -w
+LDFLAGS = -m32
 CPP_AS_FLAGS= -m32
 
 #####################################################################
 CPP=/lib/cpp
-CC = g++ -m32 -Wno-deprecated
-LD = g++ -m32 -Wno-deprecated
+CC = g++ -m32
+LD = g++ -m32
 AS = as --32
 RM = /bin/rm
 
-INCPATH = -I../network -I../filesys -I../userprog -I../threads -I../machine -I../lib -I-
+INCPATH = -iquote../network -iquote../filesys -iquote../userprog -iquote../threads -iquote../machine -iquote../lib
 
 PROGRAM = nachos
 
@@ -332,7 +332,6 @@ S_OFILES = switch.o
 OFILES = $(C_OFILES) $(S_OFILES)
 
 $(PROGRAM): $(OFILES)
-	cat ../test/*.sh ../test/Makefile ../test/*.c
 	$(LD) $(OFILES) $(LDFLAGS) -o $(PROGRAM)
 
 $(C_OFILES): %.o:
diff --git a/code/filesys/filesys.h b/code/filesys/filesys.h
index b38b08c..e8c6a0a 100644
--- a/code/filesys/filesys.h
+++ b/code/filesys/filesys.h
@@ -40,56 +40,108 @@
 #ifdef FILESYS_STUB 		// Temporarily implement file system calls as 
 				// calls to UNIX, until the real file system
 				// implementation is available
+
+typedef int OpenFileId;
+
 class FileSystem {
-  public:
-    FileSystem() { for (int i = 0; i < 20; i++) fileDescriptorTable[i] = NULL; }
+public:
+	FileSystem() { for (int i = 0; i < 20; i++) fileDescriptorTable[i] = NULL; }
 
-    bool Create(char *name) {
-      int fileDescriptor = OpenForWrite(name);
+	bool Create(char* name) {
+		int fileDescriptor = OpenForWrite(name);
+		if (fileDescriptor == -1) return FALSE;
+		Close(fileDescriptor);
+		return TRUE;
+	}
 
-      if (fileDescriptor == -1) return FALSE;
-      Close(fileDescriptor); 
-      return TRUE; 
-    }
+	OpenFile* Open(char* name) {
+		int fileDescriptor = OpenForReadWrite(name, FALSE);
+		if (fileDescriptor == -1) return NULL;
+		return new OpenFile(fileDescriptor);
+	}
 
-    OpenFile* Open(char *name) {
-      int fileDescriptor = OpenForReadWrite(name, FALSE);
+	OpenFileId OpenFiles(char* name) {
+		OpenFile* file = Open(name);
+		if (!file) return -1;
+		int freeIndex = -1;
 
-      if (fileDescriptor == -1) return NULL;
-      return new OpenFile(fileDescriptor);
-    }
+		for (int i = 0; i < 20; i++)
+			if (!fileDescriptorTable[i])
+				freeIndex = i;
 
-    bool Remove(char *name) { return Unlink(name) == 0; }
+		if (freeIndex == -1)
+			return -1;
+		OpenFileId fileDescriptor = file->GetFileDescriptor();
+		fileDescriptorTable[freeIndex] = file;
+		return fileDescriptor;
+	}
+
+	int WriteFile(char* buffer, int size, OpenFileId fd) {
+		for (int i = 0; i < 20; i++) {
+			if (!fileDescriptorTable[i])
+				continue;
+			if (fileDescriptorTable[i]->GetFileDescriptor() == fd) {
+				return fileDescriptorTable[i]->Write(buffer, size);
+			}
+		}
+		return -1;
+	}
+
+	int ReadFile(char* buffer, int size, OpenFileId fd) {
+		for (int i = 0; i < 20; i++) {
+			if (!fileDescriptorTable[i])
+				continue;
+			if (fileDescriptorTable[i]->GetFileDescriptor() == fd)
+				return fileDescriptorTable[i]->Read(buffer, size);
+		}
+		return -1;
+	}
+
+	int CloseFile(OpenFileId fd) {
+		for (int i = 0; i < 20; i++) {
+			if (!fileDescriptorTable[i])
+				continue;
+			if (fileDescriptorTable[i]->GetFileDescriptor() == fd) {
+				delete fileDescriptorTable[i];
+				fileDescriptorTable[i] = NULL;
+				return 1;
+			}
+		}
+		return 0;
+	}
+
+	bool Remove(char* name) { return Unlink(name) == 0; }
+
+	OpenFile* fileDescriptorTable[20];
 
-	  OpenFile *fileDescriptorTable[20];
 };
 
 #else // FILESYS
 class FileSystem {
-  public:
-    FileSystem(bool format);		// Initialize the file system.
-					// Must be called *after* "synchDisk" 
-					// has been initialized.
-    					// If "format", there is nothing on
-					// the disk, so initialize the directory
-    					// and the bitmap of free blocks.
+public:
+	FileSystem(bool format);		// Initialize the file system.
+	// Must be called *after* "synchDisk" 
+	// has been initialized.
+		// If "format", there is nothing on
+	// the disk, so initialize the directory
+		// and the bitmap of free blocks.
 
-    bool Create(char *name, int initialSize);  	
-					// Create a file (UNIX creat)
+	bool Create(char* name, int initialSize);
+	// Create a file (UNIX creat)
 
-    OpenFile* Open(char *name); 	// Open a file (UNIX open)
+	OpenFile* Open(char* name); 	// Open a file (UNIX open)
 
-    bool Remove(char *name);  		// Delete a file (UNIX unlink)
+	bool Remove(char* name);  		// Delete a file (UNIX unlink)
 
-    void List();			// List all the files in the file system
+	void List();			// List all the files in the file system
 
-    void Print();			// List all the files and their contents
+	void Print();			// List all the files and their contents
 
-  private:
-    OpenFile* freeMapFile;		// Bit map of free disk blocks,
-					// represented as a file
-    OpenFile* directoryFile;		// "Root" directory -- list of 
-					// file names, represented as a file
+private:
+	OpenFile* freeMapFile;		// Bit map of free disk blocks,
+	// represented as a file
+	OpenFile* directoryFile;		// "Root" directory -- list of 
+	// file names, represented as a file
 };
 
 #endif // FILESYS
diff --git a/code/filesys/openfile.h b/code/filesys/openfile.h
index af72c5c..de0f260 100644
--- a/code/filesys/openfile.h
+++ b/code/filesys/openfile.h
@@ -27,32 +27,38 @@
 #ifdef FILESYS_STUB			// Temporarily implement calls to 
 					// Nachos file system as calls to UNIX!
 					// See definitions listed under #else
+typedef int OpenFileId;
+
 class OpenFile {
   public:
     OpenFile(int f) { file = f; currentOffset = 0; }	// open the file
     ~OpenFile() { Close(file); }			// close the file
 
     int ReadAt(char *into, int numBytes, int position) { 
-    	Lseek(file, position, 0); 
-		  return ReadPartial(file, into, numBytes); 
+    		Lseek(file, position, 0); 
+		return ReadPartial(file, into, numBytes); 
 		}	
     int WriteAt(char *from, int numBytes, int position) { 
-    	Lseek(file, position, 0); 
-		  WriteFile(file, from, numBytes); 
-		  return numBytes;
+    		Lseek(file, position, 0); 
+		WriteFile(file, from, numBytes); 
+		return numBytes;
 		}	
     int Read(char *into, int numBytes) {
-      int numRead = ReadAt(into, numBytes, currentOffset); 
-		  currentOffset += numRead;
-		  return numRead;
-    }
+		int numRead = ReadAt(into, numBytes, currentOffset); 
+		currentOffset += numRead;
+		return numRead;
+    		}
     int Write(char *from, int numBytes) {
-      int numWritten = WriteAt(from, numBytes, currentOffset); 
-      currentOffset += numWritten;
-      return numWritten;
+		int numWritten = WriteAt(from, numBytes, currentOffset); 
+		currentOffset += numWritten;
+		return numWritten;
 		}
 
     int Length() { Lseek(file, 0, 2); return Tell(file); }
+
+	OpenFileId GetFileDescriptor() {
+		return file;
+	}
     
   private:
     int file;
diff --git a/code/lib/debug.h b/code/lib/debug.h
index cb5eba2..b7daf50 100644
--- a/code/lib/debug.h
+++ b/code/lib/debug.h
@@ -29,6 +29,7 @@ const char dbgFile = 'f'; 		// file system
 const char dbgAddr = 'a'; 		// address spaces
 const char dbgNet = 'n'; 		// network emulation
 const char dbgSys = 'u';                // systemcall
+const char dbgSche = 'z';
 
 class Debug {
   public:
diff --git a/code/lib/sysdep.cc b/code/lib/sysdep.cc
index c6f6dbd..a83c8da 100644
--- a/code/lib/sysdep.cc
+++ b/code/lib/sysdep.cc
@@ -308,7 +308,6 @@ int
 OpenForWrite(char *name)
 {
     int fd = open(name, O_RDWR|O_CREAT|O_TRUNC, 0666);
-    // cerr << "OpenForWrite name, fd: " << (int)name << ", " << fd << endl;
 
     ASSERT(fd >= 0); 
     return fd;
@@ -326,7 +325,6 @@ int
 OpenForReadWrite(char *name, bool crashOnError)
 {
     int fd = open(name, O_RDWR, 0);
-    // cerr << "OpenForReadWrite name, fd: " << (int)name << ", " << fd << endl;
 
     ASSERT(!crashOnError || fd >= 0);
     return fd;
diff --git a/code/machine/console.cc b/code/machine/console.cc
index d9d3d33..951398a 100644
--- a/code/machine/console.cc
+++ b/code/machine/console.cc
@@ -172,13 +172,19 @@ ConsoleOutput::PutChar(char ch)
     kernel->interrupt->Schedule(this, ConsoleTime, ConsoleWriteInt);
 }
 
+//----------------------------------------------------------------------
+// ConsoleOutput::PutInt()
+// 	Write a int to the simulated display, schedule an interrupt 
+//	to occur in the future, and return.
+//----------------------------------------------------------------------
+
 void
 ConsoleOutput::PutInt(int value)
 {
     ASSERT(putBusy == FALSE);
-    char *printStr = (char*)malloc(sizeof(char)*15);
+    char * printStr = (char*)malloc(sizeof(char) * 15);
     sprintf(printStr, "%d\n", value);
-    WriteFile(writeFileNo, printStr, strlen(printStr)*sizeof(char));
+    WriteFile(writeFileNo, printStr, strlen(printStr) * sizeof(char));
     putBusy = TRUE;
     kernel->interrupt->Schedule(this, ConsoleTime, ConsoleWriteInt);
 }
diff --git a/code/machine/console.h b/code/machine/console.h
index 2047594..1d82c92 100644
--- a/code/machine/console.h
+++ b/code/machine/console.h
@@ -76,7 +76,9 @@ class ConsoleOutput : public CallBackObj {
     void PutChar(char ch);	// Write "ch" to the console display, 
 				// and return immediately.  "callWhenDone" 
 				// will called when the I/O completes. 
-    void PutInt(int n);
+
+    void PutInt(int value);
+
     void CallBack();		// Invoked when next character can be put
 				// out to the display.
 
diff --git a/code/machine/interrupt.cc b/code/machine/interrupt.cc
index 9a1e77b..b09d17e 100644
--- a/code/machine/interrupt.cc
+++ b/code/machine/interrupt.cc
@@ -22,8 +22,8 @@
 
 #include "copyright.h"
 #include "interrupt.h"
-#include "main.h"
 #include "synchconsole.h"
+#include "main.h"
 
 // String definitions for debugging messages
 
@@ -341,7 +341,7 @@ static void
 PrintPending (PendingInterrupt *pending)
 {
     cout << "Interrupt handler "<< intTypeNames[pending->type];
-    cout << ", scheduled at " << pending->when << endl;
+    cout << ", scheduled at " << pending->when;
 }
 
 //----------------------------------------------------------------------
@@ -360,8 +360,31 @@ Interrupt::DumpState()
     cout << "\nEnd of pending interrupts\n";
 }
 
-void 
-Interrupt::PrintInt(int value)
+void Interrupt::PrintInt(int value)
 {
     kernel->synchConsoleOut->PutInt(value);
 }
+
+OpenFileId
+Interrupt::OpenFile(char *filename)
+{
+    return kernel->fileSystem->OpenFiles(filename);
+}
+
+int 
+Interrupt::WriteFile(char *buffer, int size, OpenFileId fd)
+{
+    return kernel->fileSystem->WriteFile(buffer, size, fd);
+}
+
+int 
+Interrupt::CloseFile(OpenFileId fd)
+{
+    return kernel->fileSystem->CloseFile(fd);
+}
+
+int 
+Interrupt::ReadFile(char *buffer, int size, OpenFileId fd)
+{
+    return kernel->fileSystem->ReadFile(buffer, size, fd);
+}
diff --git a/code/machine/interrupt.h b/code/machine/interrupt.h
index 7108b05..7b3f4f6 100644
--- a/code/machine/interrupt.h
+++ b/code/machine/interrupt.h
@@ -37,35 +37,41 @@
 #include "list.h"
 #include "callback.h"
 
+#include "filesys.h"
+
+typedef int OpenFileId;
+
 // 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};
+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};
+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
+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
+  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
@@ -74,72 +80,76 @@ class PendingInterrupt {
 // 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.
+public:
+  Interrupt();		// initialize the interrupt simulation
+  ~Interrupt();		// de-allocate data structures
 
-    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
+  IntStatus SetLevel(IntStatus level);
+  // Disable or enable interrupts 
+  // and return previous setting.
 
-    void Halt(); 		// quit and print out stats
+  void Enable() { (void)SetLevel(IntOn); }
+  // Enable interrupts.
+  IntStatus getLevel() { return level; }
+  // Return whether interrupts
+  // are enabled or disabled
 
-    void PrintInt(int number);
-	  int CreateFile(char *filename);
- 
-    void YieldOnReturn();	// cause a context switch on return 
-				// from an interrupt handler
+  void Idle(); 		// The ready queue is empty, roll 
+  // simulated time forward until the 
+  // next interrupt
 
-    MachineStatus getStatus() { return status; } 
-    void setStatus(MachineStatus st) { status = st; }
-        			// idle, kernel, user
+  void Halt(); 		// quit and print out stats
 
-    void DumpState();		// Print interrupt state
-    
+  void PrintInt(int number);
+  int CreateFile(char* filename);
+  OpenFileId OpenFile(char* filename);
+  int WriteFile(char* buffer, int size, OpenFileId fd);
+  int CloseFile(OpenFileId fd);
+  int ReadFile(char* buffer, int size, OpenFileId fd);
 
-    // 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 YieldOnReturn();	// cause a context switch on return 
+  // from an interrupt handler
 
-    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
+  MachineStatus getStatus() { return status; }
+  void setStatus(MachineStatus st) { status = st; }
+  // idle, kernel, user
 
-  private:
-    IntStatus level;		// are interrupts enabled or disabled?
-    SortedList<PendingInterrupt *> *pending;		
-    				// the list of interrupts scheduled
-				// to occur in the future
-    //int writeFileNo;            //UNIX file emulating the display
-    bool inHandler;		// TRUE if we are running an interrupt handler
-    //bool putBusy;               // Is a PrintInt operation in progress
-                                  //If so, you cannoot do another one
-    bool yieldOnReturn; 	// TRUE if we are to context switch
-				// on return from the interrupt handler
-    MachineStatus status;	// idle, kernel mode, user mode
+  void DumpState();		// Print interrupt state
 
-    // 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
+  // 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 ChangeLevel(IntStatus old, 	// SetLevel, without advancing the
-			IntStatus now); // simulated time
+  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
+  //int writeFileNo;            //UNIX file emulating the display
+  bool inHandler;		// TRUE if we are running an interrupt handler
+  //bool putBusy;               // Is a PrintInt operation in progress
+                                //If so, you cannoot do another one
+  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
diff --git a/code/machine/machine.cc b/code/machine/machine.cc
index 9aa234c..429d4f7 100644
--- a/code/machine/machine.cc
+++ b/code/machine/machine.cc
@@ -13,17 +13,10 @@
 
 // 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",
-  "bad memory allocation"
-};
+static char* exceptionNames[] = { "no exception", "syscall", 
+				"page fault/no TLB entry", "page read only",
+				"bus error", "address error", "overflow",
+				"illegal instruction" };
 
 //----------------------------------------------------------------------
 // CheckEndian
diff --git a/code/machine/machine.h b/code/machine/machine.h
index e601e14..bc5f1d6 100644
--- a/code/machine/machine.h
+++ b/code/machine/machine.h
@@ -28,34 +28,34 @@
 // Definitions related to the size, and format of user memory
 
 const int PageSize = 128; 		// set the page size equal to
-                              // the disk sector size, for simplicity
+					// the disk sector size, for simplicity
 
-                              //
-                              // You are allowed to change this value.
-                              // Doing so will change the number of pages of physical memory
-                              // available on the simulated machine.
-                              //
+//
+// You are allowed to change this value.
+// Doing so will change the number of pages of physical memory
+// available on the simulated machine.
+//
 const int NumPhysPages = 128;
 
 const int MemorySize = (NumPhysPages * PageSize);
 const int TLBSize = 4;			// if there is a TLB, make it small
 
-enum ExceptionType {
-  NoException,           // Everything ok!
-  SyscallException,      // A program executed a system call.
-  PageFaultException,    // No valid translation found
-  ReadOnlyException,     // Write attempted to page marked 
-                         // "read-only"
-  BusErrorException,     // Translation resulted in an 
-                         // invalid physical address
-  AddressErrorException, // Unaligned reference or one that
-                         // was beyond the end of the
-                         // address space
-  OverflowException,     // Integer overflow in add or sub.
-  IllegalInstrException, // Unimplemented or reserved instr.
-  MemoryLimitException,  // Bad allocation
+enum ExceptionType { NoException,           // Everything ok!
+		     SyscallException,      // A program executed a system call.
+		     PageFaultException,    // No valid translation found
+		     ReadOnlyException,     // Write attempted to page marked 
+					    // "read-only"
+		     BusErrorException,     // Translation resulted in an 
+					    // invalid physical address
+		     AddressErrorException, // Unaligned reference or one that
+					    // was beyond the end of the
+					    // address space
+		     OverflowException,     // Integer overflow in add or sub.
+		     IllegalInstrException, // Unimplemented or reserved instr.
+		    
+			 MemoryLimitException, // Insufficient memory
 
-  NumExceptionTypes
+		     NumExceptionTypes
 };
 
 // User program CPU state.  The full set of MIPS registers, plus a few
@@ -96,97 +96,97 @@ class Interrupt;
 class Machine {
   public:
     Machine(bool debug);	// Initialize the simulation of the hardware
-                          // for running user programs
+				// for running user programs
     ~Machine();			// De-allocate the data structures
 
-    // Routines callable by the Nachos kernel
+// Routines callable by the Nachos kernel
     void Run();	 		// Run a user program
 
     int ReadRegister(int num);	// read the contents of a CPU register
 
     void WriteRegister(int num, int value);
-    // store a value into a CPU register
+				// store a value into a CPU register
 
-    // Data structures accessible to the Nachos kernel -- main memory and the
-    // page table/TLB.
-    //
-    // Note that *all* communication between the user program and the kernel 
-    // are in terms of these data structures (plus the CPU registers).
+// Data structures accessible to the Nachos kernel -- main memory and the
+// page table/TLB.
+//
+// Note that *all* communication between the user program and the kernel 
+// are in terms of these data structures (plus the CPU registers).
 
     char *mainMemory;		// physical memory to store user program,
-                        // code and data, while executing
+				// code and data, while executing
 
-                        // NOTE: the hardware translation of virtual addresses in the user program
-                        // to physical addresses (relative to the beginning of "mainMemory")
-                        // can be controlled by one of:
-                        //	a traditional linear page table
-                        //  	a software-loaded translation lookaside buffer (tlb) -- a cache of 
-                        //	  mappings of virtual page #'s to physical page #'s
-                        //
-                        // If "tlb" is NULL, the linear page table is used
-                        // If "tlb" is non-NULL, the Nachos kernel is responsible for managing
-                        //	the contents of the TLB.  But the kernel can use any data structure
-                        //	it wants (eg, segmented paging) for handling TLB cache misses.
-                        // 
-                        // For simplicity, both the page table pointer and the TLB pointer are
-                        // public.  However, while there can be multiple page tables (one per address
-                        // space, stored in memory), there is only one TLB (implemented in hardware).
-                        // Thus the TLB pointer should be considered as *read-only*, although 
-                        // the contents of the TLB are free to be modified by the kernel software.
+// NOTE: the hardware translation of virtual addresses in the user program
+// to physical addresses (relative to the beginning of "mainMemory")
+// can be controlled by one of:
+//	a traditional linear page table
+//  	a software-loaded translation lookaside buffer (tlb) -- a cache of 
+//	  mappings of virtual page #'s to physical page #'s
+//
+// If "tlb" is NULL, the linear page table is used
+// If "tlb" is non-NULL, the Nachos kernel is responsible for managing
+//	the contents of the TLB.  But the kernel can use any data structure
+//	it wants (eg, segmented paging) for handling TLB cache misses.
+// 
+// For simplicity, both the page table pointer and the TLB pointer are
+// public.  However, while there can be multiple page tables (one per address
+// space, stored in memory), there is only one TLB (implemented in hardware).
+// Thus the TLB pointer should be considered as *read-only*, although 
+// the contents of the TLB are free to be modified by the kernel software.
 
     TranslationEntry *tlb;		// this pointer should be considered 
-                              // "read-only" to Nachos kernel code
+					// "read-only" to Nachos kernel code
 
     TranslationEntry *pageTable;
     unsigned int pageTableSize;
 
     bool ReadMem(int addr, int size, int* value);
     bool WriteMem(int addr, int size, int value);
-    // Read or write 1, 2, or 4 bytes of virtual 
-    // memory (at addr).  Return FALSE if a 
-    // correct translation couldn't be found.
+    				// Read or write 1, 2, or 4 bytes of virtual 
+				// memory (at addr).  Return FALSE if a 
+				// correct translation couldn't be found.
   private:
 
-    // Routines internal to the machine simulation -- DO NOT call these directly
+// Routines internal to the machine simulation -- DO NOT call these directly
     void DelayedLoad(int nextReg, int nextVal);  	
-    // Do a pending delayed load (modifying a reg)
+				// Do a pending delayed load (modifying a reg)
 
     void OneInstruction(Instruction *instr); 	
-    // Run one instruction of a user program.
-
+    				// Run one instruction of a user program.
+    
 
 
     ExceptionType Translate(int virtAddr, int* physAddr, int size,bool writing);
-    // Translate an address, and check for 
-    // alignment.  Set the use and dirty bits in 
-    // the translation entry appropriately,
-    // and return an exception code if the 
-    // translation couldn't be completed.
+    				// Translate an address, and check for 
+				// alignment.  Set the use and dirty bits in 
+				// the translation entry appropriately,
+    				// and return an exception code if the 
+				// translation couldn't be completed.
 
     void RaiseException(ExceptionType which, int badVAddr);
-    // Trap to the Nachos kernel, because of a
-    // system call or other exception.  
+				// Trap to the Nachos kernel, because of a
+				// system call or other exception.  
 
     void Debugger();		// invoke the user program debugger
     void DumpState();		// print the user CPU and memory state 
 
 
-    // Internal data structures
+// Internal data structures
 
     int registers[NumTotalRegs]; // CPU registers, for executing user programs
 
     bool singleStep;		// drop back into the debugger after each
-                        // simulated instruction
+				// simulated instruction
     int runUntilTime;		// drop back into the debugger when simulated
-                        // time reaches this value
+				// time reaches this value
 
     friend class Interrupt;		// calls DelayedLoad()    
 };
 
 extern void ExceptionHandler(ExceptionType which);
-// Entry point into Nachos for handling
-// user system calls and exceptions
-// Defined in exception.cc
+				// Entry point into Nachos for handling
+				// user system calls and exceptions
+				// Defined in exception.cc
 
 
 // Routines for converting Words and Short Words to and from the
diff --git a/code/machine/stats.h b/code/machine/stats.h
index 946c3b9..48ea46f 100644
--- a/code/machine/stats.h
+++ b/code/machine/stats.h
@@ -20,25 +20,25 @@
 // The fields in this class are public to make it easier to update.
 
 class Statistics {
-  public:
-    int totalTicks;      	// Total time running Nachos
-    int idleTicks;       	// Time spent idle (no threads to run)
-    int systemTicks;	 	// Time spent executing system code
-    int userTicks;       	// Time spent executing user code
-				// (this is also equal to # of
-				// user instructions executed)
+public:
+  int totalTicks;      	// Total time running Nachos
+  int idleTicks;       	// Time spent idle (no threads to run)
+  int systemTicks;	 	// Time spent executing system code
+  int userTicks;       	// Time spent executing user code
+  // (this is also equal to # of
+  // user instructions executed)
 
-    int numDiskReads;		// number of disk read requests
-    int numDiskWrites;		// number of disk write requests
-    int numConsoleCharsRead;	// number of characters read from the keyboard
-    int numConsoleCharsWritten; // number of characters written to the display
-    int numPageFaults;		// number of virtual memory page faults
-    int numPacketsSent;		// number of packets sent over the network
-    int numPacketsRecvd;	// number of packets received over the network
+  int numDiskReads;		// number of disk read requests
+  int numDiskWrites;		// number of disk write requests
+  int numConsoleCharsRead;	// number of characters read from the keyboard
+  int numConsoleCharsWritten; // number of characters written to the display
+  int numPageFaults;		// number of virtual memory page faults
+  int numPacketsSent;		// number of packets sent over the network
+  int numPacketsRecvd;	// number of packets received over the network
 
-    Statistics(); 		// initialize everything to zero
+  Statistics(); 		// initialize everything to zero
 
-    void Print();		// print collected statistics
+  void Print();		// print collected statistics
 };
 
 // Constants used to reflect the relative time an operation would
@@ -49,12 +49,15 @@ class Statistics {
 // in the kernel measured by the number of calls to enable interrupts,
 // these time constants are none too exact.
 
-const int UserTick = 	   1;	// advance for each user-level instruction 
-const int SystemTick =	  10; 	// advance each time interrupts are enabled
+const int UserTick = 1;	// advance for each user-level instruction 
+const int SystemTick = 10; 	// advance each time interrupts are enabled
 const int RotationTime = 500; 	// time disk takes to rotate one sector
-const int SeekTime =	 500;  	// time disk takes to seek past one track
-const int ConsoleTime =	 100;	// time to read or write one character
-const int NetworkTime =	 100;  	// time to send or receive one packet
-const int TimerTicks = 	 100;  	// (average) time between timer interrupts
+const int SeekTime = 500;  	// time disk takes to seek past one track
+
+// MP4 MODIFIED
+const int ConsoleTime = 1;	// time to read or write one character
+
+const int NetworkTime = 100;  	// time to send or receive one packet
+const int TimerTicks = 100;  	// (average) time between timer interrupts
 
 #endif // STATS_H
diff --git a/code/machine/translate.cc b/code/machine/translate.cc
index 7b92fe6..969203b 100644
--- a/code/machine/translate.cc
+++ b/code/machine/translate.cc
@@ -85,38 +85,38 @@ ShortToMachine(unsigned short shortword) { return ShortToHost(shortword); }
 bool
 Machine::ReadMem(int addr, int size, int *value)
 {
-  int data;
-  ExceptionType exception;
-  int physicalAddress;
+    int data;
+    ExceptionType exception;
+    int physicalAddress;
+    
+    DEBUG(dbgAddr, "Reading VA " << addr << ", size " << size);
+    
+    exception = Translate(addr, &physicalAddress, size, FALSE);
+    if (exception != NoException) {
+	RaiseException(exception, addr);
+	return FALSE;
+    }
+    switch (size) {
+      case 1:
+	data = mainMemory[physicalAddress];
+	*value = data;
+	break;
+	
+      case 2:
+	data = *(unsigned short *) &mainMemory[physicalAddress];
+	*value = ShortToHost(data);
+	break;
+	
+      case 4:
+	data = *(unsigned int *) &mainMemory[physicalAddress];
+	*value = WordToHost(data);
+	break;
 
-  DEBUG(dbgAddr, "Reading VA " << addr << ", size " << size);
-
-  exception = Translate(addr, &physicalAddress, size, FALSE);
-  if (exception != NoException) {
-    RaiseException(exception, addr);
-    return FALSE;
-  }
-  switch (size) {
-    case 1:
-      data = mainMemory[physicalAddress];
-      *value = data;
-      break;
-
-    case 2:
-      data = *(unsigned short *) &mainMemory[physicalAddress];
-      *value = ShortToHost(data);
-      break;
-
-    case 4:
-      data = *(unsigned int *) &mainMemory[physicalAddress];
-      *value = WordToHost(data);
-      break;
-
-    default: ASSERT(FALSE);
-  }
-
-  DEBUG(dbgAddr, "\tvalue read = " << *value);
-  return (TRUE);
+      default: ASSERT(FALSE);
+    }
+    
+    DEBUG(dbgAddr, "\tvalue read = " << *value);
+    return (TRUE);
 }
 
 //----------------------------------------------------------------------
@@ -135,35 +135,35 @@ Machine::ReadMem(int addr, int size, int *value)
 bool
 Machine::WriteMem(int addr, int size, int value)
 {
-  ExceptionType exception;
-  int physicalAddress;
+    ExceptionType exception;
+    int physicalAddress;
+     
+    DEBUG(dbgAddr, "Writing VA " << addr << ", size " << size << ", value " << value);
 
-  DEBUG(dbgAddr, "Writing VA " << addr << ", size " << size << ", value " << value);
+    exception = Translate(addr, &physicalAddress, size, TRUE);
+    if (exception != NoException) {
+	RaiseException(exception, addr);
+	return FALSE;
+    }
+    switch (size) {
+      case 1:
+	mainMemory[physicalAddress] = (unsigned char) (value & 0xff);
+	break;
 
-  exception = Translate(addr, &physicalAddress, size, TRUE);
-  if (exception != NoException) {
-    RaiseException(exception, addr);
-    return FALSE;
-  }
-  switch (size) {
-    case 1:
-      mainMemory[physicalAddress] = (unsigned char) (value & 0xff);
-      break;
-
-    case 2:
-      *(unsigned short *) &mainMemory[physicalAddress]
-        = ShortToMachine((unsigned short) (value & 0xffff));
-      break;
-
-    case 4:
-      *(unsigned int *) &mainMemory[physicalAddress]
-        = WordToMachine((unsigned int) value);
-      break;
-
-    default: ASSERT(FALSE);
-  }
-
-  return TRUE;
+      case 2:
+	*(unsigned short *) &mainMemory[physicalAddress]
+		= ShortToMachine((unsigned short) (value & 0xffff));
+	break;
+      
+      case 4:
+	*(unsigned int *) &mainMemory[physicalAddress]
+		= WordToMachine((unsigned int) value);
+	break;
+	
+      default: ASSERT(FALSE);
+    }
+    
+    return TRUE;
 }
 
 //----------------------------------------------------------------------
@@ -184,75 +184,67 @@ Machine::WriteMem(int addr, int size, int value)
 ExceptionType
 Machine::Translate(int virtAddr, int* physAddr, int size, bool writing)
 {
-  int i;
-  unsigned int vpn, offset;
-  TranslationEntry *entry;
-  unsigned int pageFrame;
+    int i;
+    unsigned int vpn, offset;
+    TranslationEntry *entry;
+    unsigned int pageFrame;
 
-  DEBUG(dbgAddr, "\tTranslate " << virtAddr << (writing ? " , write" : " , read"));
+    DEBUG(dbgAddr, "\tTranslate " << virtAddr << (writing ? " , write" : " , read"));
 
-  // check for alignment errors
-  if (((size == 4) && (virtAddr & 0x3)) || ((size == 2) && (virtAddr & 0x1))){
-    DEBUG(dbgAddr, "Alignment problem at " << virtAddr << ", size " << size);
-    return AddressErrorException;
-  }
-  // we must have either a TLB or a page table, but not both!
-  ASSERT(tlb == NULL || pageTable == NULL);	
-  ASSERT(tlb != NULL || pageTable != NULL);	
-
-  // calculate the virtual page number, and offset within the page,
-  // from the virtual address
-  vpn = (unsigned) virtAddr / PageSize;
-  offset = (unsigned) virtAddr % PageSize;
-
-  if (tlb == NULL) {		// => page table => vpn is index into table
-    if (vpn >= pageTableSize) {
-      DEBUG(dbgAddr, "Illegal virtual page # " << virtAddr);
-      DEBUG(dbgAddr, "vpn, pageTableSize, NumPhysPages: " << vpn << ' ' << pageTableSize << ' ' << NumPhysPages);
-      return AddressErrorException;
-    } else if (!pageTable[vpn].valid) {
-      DEBUG(dbgAddr, "Invalid virtual page # " << virtAddr);
-      return PageFaultException;
+// check for alignment errors
+    if (((size == 4) && (virtAddr & 0x3)) || ((size == 2) && (virtAddr & 0x1))){
+	DEBUG(dbgAddr, "Alignment problem at " << virtAddr << ", size " << size);
+	return AddressErrorException;
     }
-    entry = &pageTable[vpn];
-  } else {
-    for (entry = NULL, i = 0; i < TLBSize; i++)
-      if (tlb[i].valid && (tlb[i].virtualPage == ((int)vpn))) {
-        entry = &tlb[i];			// FOUND!
-        break;
-      }
-    if (entry == NULL) {				// not found
-      DEBUG(dbgAddr, "Invalid TLB entry for this virtual page!");
-      return PageFaultException;		// really, this is a TLB fault,
-                                    // the page may be in memory,
-                                    // but not in the TLB
-    }
-  }
+    // we must have either a TLB or a page table, but not both!
+    ASSERT(tlb == NULL || pageTable == NULL);	
+    ASSERT(tlb != NULL || pageTable != NULL);	
 
-  if (entry->readOnly && writing) {	// trying to write to a read-only page
-    DEBUG(dbgAddr, "Write to read-only page at " << virtAddr);
-    return ReadOnlyException;
-  }
-  pageFrame = entry->physicalPage;
-  if (pageFrame == -1) {
-    pageFrame = entry->physicalPage = kernel->frameTable->Allocate();
-    if (pageFrame == -1) {
-      DEBUG(dbgAddr, "Memory Limit exceeded");
-      return MemoryLimitException;
+// calculate the virtual page number, and offset within the page,
+// from the virtual address
+    vpn = (unsigned) virtAddr / PageSize;
+    offset = (unsigned) virtAddr % PageSize;
+    
+    if (tlb == NULL) {		// => page table => vpn is index into table
+	if (vpn >= pageTableSize) {
+	    DEBUG(dbgAddr, "Illegal virtual page # " << virtAddr);
+	    return AddressErrorException;
+	} else if (!pageTable[vpn].valid) {
+	    DEBUG(dbgAddr, "Invalid virtual page # " << virtAddr);
+	    return PageFaultException;
+	}
+	entry = &pageTable[vpn];
+    } else {
+        for (entry = NULL, i = 0; i < TLBSize; i++)
+    	    if (tlb[i].valid && (tlb[i].virtualPage == ((int)vpn))) {
+		entry = &tlb[i];			// FOUND!
+		break;
+	    }
+	if (entry == NULL) {				// not found
+    	    DEBUG(dbgAddr, "Invalid TLB entry for this virtual page!");
+    	    return PageFaultException;		// really, this is a TLB fault,
+						// the page may be in memory,
+						// but not in the TLB
+	}
     }
-  }
 
-  // if the pageFrame is too big, there is something really wrong! 
-  // An invalid translation was loaded into the page table or TLB. 
-  if (pageFrame >= NumPhysPages) { 
-    DEBUG(dbgAddr, "Illegal pageframe " << pageFrame);
-    return BusErrorException;
-  }
-  entry->use = TRUE;		// set the use, dirty bits
-  if (writing)
-    entry->dirty = TRUE;
-  *physAddr = pageFrame * PageSize + offset;
-  ASSERT((*physAddr >= 0) && ((*physAddr + size) <= MemorySize));
-  DEBUG(dbgAddr, "phys addr = " << *physAddr);
-  return NoException;
+    if (entry->readOnly && writing) {	// trying to write to a read-only page
+	DEBUG(dbgAddr, "Write to read-only page at " << virtAddr);
+	return ReadOnlyException;
+    }
+    pageFrame = entry->physicalPage;
+
+    // if the pageFrame is too big, there is something really wrong! 
+    // An invalid translation was loaded into the page table or TLB. 
+    if (pageFrame >= NumPhysPages) { 
+	DEBUG(dbgAddr, "Illegal pageframe " << pageFrame);
+	return BusErrorException;
+    }
+    entry->use = TRUE;		// set the use, dirty bits
+    if (writing)
+	entry->dirty = TRUE;
+    *physAddr = pageFrame * PageSize + offset;
+    ASSERT((*physAddr >= 0) && ((*physAddr + size) <= MemorySize));
+    DEBUG(dbgAddr, "phys addr = " << *physAddr);
+    return NoException;
 }
diff --git a/code/test/Makefile b/code/test/Makefile
index 3ca2e99..b1fb223 100644
--- a/code/test/Makefile
+++ b/code/test/Makefile
@@ -113,8 +113,7 @@ ifeq ($(hosttype),unknown)
 PROGRAMS = unknownhost
 else
 # change this if you create a new test program!
-PROGRAMS = add halt consoleIO_test1 consoleIO_test2 fileIO_test1 fileIO_test2 test
-# PROGRAMS = halt
+PROGRAMS = mp4_consoleIO_1 mp4_consoleIO_2 mp4_consoleIO_3 mp4_consoleIO_4
 endif
 
 all: $(PROGRAMS)
@@ -122,78 +121,35 @@ all: $(PROGRAMS)
 start.o: start.S ../userprog/syscall.h
 	$(CC) $(CFLAGS) $(ASFLAGS) -c start.S
 
-halt.o: halt.c
-	$(CC) $(CFLAGS) -c halt.c
-halt: halt.o start.o
-	$(LD) $(LDFLAGS) start.o halt.o -o halt.coff
-	$(COFF2NOFF) halt.coff halt
+mp4_consoleIO_1.o: mp4_consoleIO_1.c
+	$(CC) $(CFLAGS) -c mp4_consoleIO_1.c
 
-add.o: add.c
-	$(CC) $(CFLAGS) -c add.c
+mp4_consoleIO_1: mp4_consoleIO_1.o start.o
+	$(LD) $(LDFLAGS) start.o mp4_consoleIO_1.o -o mp4_consoleIO_1.coff
+	$(COFF2NOFF) mp4_consoleIO_1.coff mp4_consoleIO_1
 
-add: add.o start.o
-	$(LD) $(LDFLAGS) start.o add.o -o add.coff
-	$(COFF2NOFF) add.coff add
 
-shell.o: shell.c
-	$(CC) $(CFLAGS) -c shell.c
-shell: shell.o start.o
-	$(LD) $(LDFLAGS) start.o shell.o -o shell.coff
-	$(COFF2NOFF) shell.coff shell
+mp4_consoleIO_2.o: mp4_consoleIO_2.c
+	$(CC) $(CFLAGS) -c mp4_consoleIO_2.c
 
-sort.o: sort.c
-	$(CC) $(CFLAGS) -c sort.c
-sort: sort.o start.o
-	$(LD) $(LDFLAGS) start.o sort.o -o sort.coff
-	$(COFF2NOFF) sort.coff sort
+mp4_consoleIO_2: mp4_consoleIO_2.o start.o
+	$(LD) $(LDFLAGS) start.o mp4_consoleIO_2.o -o mp4_consoleIO_2.coff
+	$(COFF2NOFF) mp4_consoleIO_2.coff mp4_consoleIO_2
 
-segments.o: segments.c
-	$(CC) $(CFLAGS) -c segments.c
-segments: segments.o start.o
-	$(LD) $(LDFLAGS) start.o segments.o -o segments.coff
-	$(COFF2NOFF) segments.coff segments
+mp4_consoleIO_3.o: mp4_consoleIO_3.c
+	$(CC) $(CFLAGS) -c mp4_consoleIO_3.c
 
-matmult.o: matmult.c
-	$(CC) $(CFLAGS) -c matmult.c
-matmult: matmult.o start.o
-	$(LD) $(LDFLAGS) start.o matmult.o -o matmult.coff
-	$(COFF2NOFF) matmult.coff matmult
+mp4_consoleIO_3: mp4_consoleIO_3.o start.o
+	$(LD) $(LDFLAGS) start.o mp4_consoleIO_3.o -o mp4_consoleIO_3.coff
+	$(COFF2NOFF) mp4_consoleIO_3.coff mp4_consoleIO_3
 
-consoleIO_test1.o: consoleIO_test1.c
-	$(CC) $(CFLAGS) -c consoleIO_test1.c
-consoleIO_test1: consoleIO_test1.o start.o
-	$(LD) $(LDFLAGS) start.o consoleIO_test1.o -o consoleIO_test1.coff
-	$(COFF2NOFF) consoleIO_test1.coff consoleIO_test1
+mp4_consoleIO_4.o: mp4_consoleIO_4.c
+	$(CC) $(CFLAGS) -c mp4_consoleIO_4.c
 
-consoleIO_test2.o: consoleIO_test2.c
-	$(CC) $(CFLAGS) -c consoleIO_test2.c
-consoleIO_test2: consoleIO_test2.o start.o
-	$(LD) $(LDFLAGS) start.o consoleIO_test2.o -o consoleIO_test2.coff
-	$(COFF2NOFF) consoleIO_test2.coff consoleIO_test2
+mp4_consoleIO_4: mp4_consoleIO_4.o start.o
+	$(LD) $(LDFLAGS) start.o mp4_consoleIO_4.o -o mp4_consoleIO_4.coff
+	$(COFF2NOFF) mp4_consoleIO_4.coff mp4_consoleIO_4
 	
-fileIO_test1.o: fileIO_test1.c
-	$(CC) $(CFLAGS) -c fileIO_test1.c
-fileIO_test1: fileIO_test1.o start.o
-	$(LD) $(LDFLAGS) start.o fileIO_test1.o -o fileIO_test1.coff
-	$(COFF2NOFF) fileIO_test1.coff fileIO_test1
-	
-fileIO_test2.o: fileIO_test2.c
-	$(CC) $(CFLAGS) -c fileIO_test2.c
-fileIO_test2: fileIO_test2.o start.o
-	$(LD) $(LDFLAGS) start.o fileIO_test2.o -o fileIO_test2.coff
-	$(COFF2NOFF) fileIO_test2.coff fileIO_test2
-
-fileIO_test3.o: fileIO_test3.c
-	$(CC) $(CFLAGS) -c fileIO_test3.c
-fileIO_test3: fileIO_test3.o start.o
-	$(LD) $(LDFLAGS) start.o fileIO_test3.o -o fileIO_test3.coff
-	$(COFF2NOFF) fileIO_test3.coff fileIO_test3
-
-test.o: test.c
-	$(CC) $(CFLAGS) -c test.c
-test: test.o start.o
-	$(LD) $(LDFLAGS) start.o test.o -o test.coff
-	$(COFF2NOFF) test.coff test
 
 clean:
 	$(RM) -f *.o *.ii
@@ -203,12 +159,11 @@ distclean: clean
 	$(RM) -f $(PROGRAMS)
 
 run: $(PROGRAMS)
-	timeout 1 $(NACHOS) -e consoleIO_test1 -e consoleIO_test2
+	timeout 1 $(NACHOS) -ep mp4_consoleIO_1 70 -ep mp4_consoleIO_3 80 -ep mp4_consoleIO_2 50
 	echo 'done'
 
 debug: $(PROGRAMS)
-	timeout 1 $(NACHOS) -e consoleIO_test1 -e consoleIO_test2 -d +
-
+	timeout 1 $(NACHOS) -d z -ep mp4_consoleIO_1 60 -ep mp4_consoleIO_2 70
 
 unknownhost:
 	@echo Host type could not be determined.
diff --git a/code/test/mp4_consoleIO_1.c b/code/test/mp4_consoleIO_1.c
new file mode 100644
index 0000000..7f64e4e
--- /dev/null
+++ b/code/test/mp4_consoleIO_1.c
@@ -0,0 +1,10 @@
+#include "syscall.h"
+
+int main()
+{
+	int n;
+	for (n = 0; n < 4; n++) {
+		PrintInt(1);
+	}
+	return 0;
+}
diff --git a/code/test/mp4_consoleIO_2.c b/code/test/mp4_consoleIO_2.c
new file mode 100644
index 0000000..3efa141
--- /dev/null
+++ b/code/test/mp4_consoleIO_2.c
@@ -0,0 +1,9 @@
+#include "syscall.h"
+int main()
+{
+	int n;
+	for (n = 0; n < 5; n++) {
+		PrintInt(2);
+	}
+	return 0;
+}
diff --git a/code/test/mp4_consoleIO_3.c b/code/test/mp4_consoleIO_3.c
new file mode 100644
index 0000000..1e265c8
--- /dev/null
+++ b/code/test/mp4_consoleIO_3.c
@@ -0,0 +1,10 @@
+#include "syscall.h"
+int
+main()
+{
+	int n;
+	for (n = 0; n < 12; n++) {
+		PrintInt(3);
+	}
+	return 0;
+}
diff --git a/code/test/mp4_consoleIO_4.c b/code/test/mp4_consoleIO_4.c
new file mode 100644
index 0000000..888191d
--- /dev/null
+++ b/code/test/mp4_consoleIO_4.c
@@ -0,0 +1,9 @@
+#include "syscall.h"
+int main()
+{
+    int n;
+    for (n = 0; n < 11; n++) {
+        PrintInt(4);
+    }
+    return 0;
+}
diff --git a/code/test/os_students.sh b/code/test/os_students.sh
index 9f7eada..2b3b450 100644
--- a/code/test/os_students.sh
+++ b/code/test/os_students.sh
@@ -1,4 +1,9 @@
 make distclean
-make
-timeout 1 ../build.linux/nachos -e consoleIO_test1 -e consoleIO_test2
-echo 'done'
+make 
+rm -f *.o *.ii
+rm -f *.coff
+echo "=========================="
+timeout 1 ../build.linux/nachos -e mp4_consoleIO_1 -e mp4_consoleIO_2 
+echo "=========================="
+timeout 1 ../build.linux/nachos -e mp4_consoleIO_3 -e mp4_consoleIO_4
+echo "done"
\ No newline at end of file
diff --git a/code/test/start.S b/code/test/start.S
index 0e7a7a7..2acb37a 100644
--- a/code/test/start.S
+++ b/code/test/start.S
@@ -58,6 +58,14 @@ MSG:
 	j	$31
 	.end MSG
 
+	.globl PrintInt
+	.ent   PrintInt
+PrintInt:
+	addiu $2,$0,SC_PrintInt
+	syscall
+	j	$31
+	.end PrintInt
+
 	.globl Add
 	.ent	Add
 Add:
@@ -186,14 +194,6 @@ ThreadJoin:
 	j 	$31
 	.end ThreadJoin
 
-	.globl PrintInt
-	.ent	 PrintInt
-PrintInt:
-	addiu   $2,$0,SC_PrintInt
-	syscall
-	j       $31
-	.end    PrintInt
-
 
 /* dummy function to keep gcc happy */
         .globl  __main
diff --git a/code/threads/alarm.cc b/code/threads/alarm.cc
index 4cd1248..f230fb7 100644
--- a/code/threads/alarm.cc
+++ b/code/threads/alarm.cc
@@ -43,13 +43,15 @@ Alarm::Alarm(bool doRandom)
 //      if we're currently running something (in other words, not idle).
 //----------------------------------------------------------------------
 
-void 
-Alarm::CallBack() 
+void
+Alarm::CallBack()
 {
-    Interrupt *interrupt = kernel->interrupt;
+    Interrupt* interrupt = kernel->interrupt;
     MachineStatus status = interrupt->getStatus();
-    
+
+    // Todo ----
     if (status != IdleMode) {
-	interrupt->YieldOnReturn();
+        // interrupt->YieldOnReturn();
     }
+    // ---------
 }
diff --git a/code/threads/kernel.cc b/code/threads/kernel.cc
index 81000b1..00f0af4 100644
--- a/code/threads/kernel.cc
+++ b/code/threads/kernel.cc
@@ -24,11 +24,9 @@
 //	for the initialization (see also comments in main.cc)  
 //----------------------------------------------------------------------
 
-Kernel::Kernel(int argc, char **argv)
+Kernel::Kernel(int argc, char** argv)
 {
-  execfileNum = 0;
-  threadNum = 0;
-  randomSlice = FALSE; 
+  randomSlice = FALSE;
   debugUserProg = FALSE;
   consoleIn = NULL;          // default is stdin
   consoleOut = NULL;         // default is stdout
@@ -45,32 +43,48 @@ Kernel::Kernel(int argc, char **argv)
                                     // number generator
       randomSlice = TRUE;
       i++;
-    } else if (strcmp(argv[i], "-s") == 0) {
+    }
+    else if (strcmp(argv[i], "-s") == 0) {
       debugUserProg = TRUE;
-    } else if (strcmp(argv[i], "-e") == 0) {
-      execfile[++execfileNum]= argv[++i];
+    }
+    // Todo ----
+    else if (strcmp(argv[i], "-e") == 0) {
+      execfile[++execfileNum] = argv[++i];
       cout << execfile[execfileNum] << "\n";
-    } else if (strcmp(argv[i], "-ci") == 0) {
+    }
+    else if (strcmp(argv[i], "-ep") == 0) {
+      execfile[++execfileNum] = argv[++i];
+      execPriority[execfileNum] = atoi(argv[++i]);
+      cout << execfile[execfileNum] << " with priority "
+        << execPriority[execfileNum] << "\n";
+    }
+    // ---------
+    else if (strcmp(argv[i], "-ci") == 0) {
       ASSERT(i + 1 < argc);
       consoleIn = argv[i + 1];
       i++;
-    } else if (strcmp(argv[i], "-co") == 0) {
+    }
+    else if (strcmp(argv[i], "-co") == 0) {
       ASSERT(i + 1 < argc);
       consoleOut = argv[i + 1];
       i++;
 #ifndef FILESYS_STUB
-    } else if (strcmp(argv[i], "-f") == 0) {
+    }
+    else if (strcmp(argv[i], "-f") == 0) {
       formatFlag = TRUE;
 #endif
-    } else if (strcmp(argv[i], "-n") == 0) {
+    }
+    else if (strcmp(argv[i], "-n") == 0) {
       ASSERT(i + 1 < argc);   // next argument is float
       reliability = atof(argv[i + 1]);
       i++;
-    } else if (strcmp(argv[i], "-m") == 0) {
+    }
+    else if (strcmp(argv[i], "-m") == 0) {
       ASSERT(i + 1 < argc);   // next argument is int
       hostName = atoi(argv[i + 1]);
       i++;
-    } else if (strcmp(argv[i], "-u") == 0) {
+    }
+    else if (strcmp(argv[i], "-u") == 0) {
       cout << "Partial usage: nachos [-rs randomSeed]\n";
       cout << "Partial usage: nachos [-s]\n";
       cout << "Partial usage: nachos [-ci consoleIn] [-co consoleOut]\n";
@@ -92,32 +106,34 @@ Kernel::Kernel(int argc, char **argv)
 void
 Kernel::Initialize()
 {
-  // We didn't explicitly allocate the current thread we are running in.
-  // But if it ever tries to give up the CPU, we better have a Thread
-  // object to save its state. 
+    // We didn't explicitly allocate the current thread we are running in.
+    // But if it ever tries to give up the CPU, we better have a Thread
+    // object to save its state. 
 
 
-  currentThread = new Thread("main", threadNum++);		
-  currentThread->setStatus(RUNNING);
+    currentThread = new Thread("main", threadNum++);
+    currentThread->setStatus(RUNNING);
 
-  stats = new Statistics();		// collect statistics
-  interrupt = new Interrupt;		// start up interrupt handling
-  scheduler = new Scheduler();	// initialize the ready queue
-  alarm = new Alarm(randomSlice);	// start up time slicing
-  machine = new Machine(debugUserProg);
-  synchConsoleIn = new SynchConsoleInput(consoleIn); // input from stdin
-  synchConsoleOut = new SynchConsoleOutput(consoleOut); // output to stdout
-  synchDisk = new SynchDisk();    //
+    stats = new Statistics();		// collect statistics
+    interrupt = new Interrupt;		// start up interrupt handling
+    scheduler = new Scheduler();	// initialize the ready queue
+    alarm = new Alarm(randomSlice);	// start up time slicing
+    machine = new Machine(debugUserProg);
+    synchConsoleIn = new SynchConsoleInput(consoleIn); // input from stdin
+    synchConsoleOut = new SynchConsoleOutput(consoleOut); // output to stdout
+    synchDisk = new SynchDisk();    //
 #ifdef FILESYS_STUB
-  fileSystem = new FileSystem();
+    fileSystem = new FileSystem();
 #else
-  fileSystem = new FileSystem(formatFlag);
+    fileSystem = new FileSystem(formatFlag);
 #endif // FILESYS_STUB
-  postOfficeIn = new PostOfficeInput(10);
-  postOfficeOut = new PostOfficeOutput(reliability);
-  frameTable = new FrameTable;
 
-  interrupt->Enable();
+    // MP4 MODIFIED
+    // postOfficeIn = new PostOfficeInput(10);
+    // postOfficeOut = new PostOfficeOutput(reliability);
+
+    frameTable = new FrameTable();
+    interrupt->Enable();
 }
 
 //----------------------------------------------------------------------
@@ -127,20 +143,23 @@ Kernel::Initialize()
 
 Kernel::~Kernel()
 {
-  delete stats;
-  delete interrupt;
-  delete scheduler;
-  delete alarm;
-  delete machine;
-  delete synchConsoleIn;
-  delete synchConsoleOut;
-  delete synchDisk;
-  delete fileSystem;
-  delete postOfficeIn;
-  delete postOfficeOut;
-  delete frameTable;
+    delete stats;
+    delete interrupt;
+    delete scheduler;
+    delete alarm;
+    delete machine;
+    delete synchConsoleIn;
+    delete synchConsoleOut;
+    delete synchDisk;
+    delete fileSystem;
 
-  Exit(0);
+    // MP4 MODIFIED
+    // delete postOfficeIn;
+    // delete postOfficeOut;
+
+    delete frameTable;
+
+    Exit(0);
 }
 
 //----------------------------------------------------------------------
@@ -150,23 +169,23 @@ Kernel::~Kernel()
 
 void
 Kernel::ThreadSelfTest() {
-   Semaphore *semaphore;
-   SynchList<int> *synchList;
-   
-   LibSelfTest();		// test library routines
-   
-   currentThread->SelfTest();	// test thread switching
-   
-   				// test semaphore operation
-   semaphore = new Semaphore("test", 0);
-   semaphore->SelfTest();
-   delete semaphore;
-   
-   				// test locks, condition variables
-				// using synchronized lists
-   synchList = new SynchList<int>;
-   synchList->SelfTest(9);
-   delete synchList;
+    Semaphore* semaphore;
+    SynchList<int>* synchList;
+
+    LibSelfTest();		// test library routines
+
+    currentThread->SelfTest();	// test thread switching
+
+    // test semaphore operation
+    semaphore = new Semaphore("test", 0);
+    semaphore->SelfTest();
+    delete semaphore;
+
+    // test locks, condition variables
+    // using synchronized lists
+    synchList = new SynchList<int>;
+    synchList->SelfTest(9);
+    delete synchList;
 
 }
 
@@ -179,14 +198,14 @@ void
 Kernel::ConsoleTest() {
     char ch;
 
-    cout << "Testing the console device.\n" 
+    cout << "Testing the console device.\n"
         << "Typed characters will be echoed, until ^D is typed.\n"
         << "Note newlines are needed to flush input through UNIX.\n";
     cout.flush();
 
     do {
         ch = synchConsoleIn->GetChar();
-        if(ch != EOF) synchConsoleOut->PutChar(ch);   // echo it!
+        if (ch != EOF) synchConsoleOut->PutChar(ch);   // echo it!
     } while (ch != EOF);
 
     cout << "\n";
@@ -211,28 +230,28 @@ Kernel::NetworkTest() {
 
     if (hostName == 0 || hostName == 1) {
         // if we're machine 1, send to 0 and vice versa
-        int farHost = (hostName == 0 ? 1 : 0); 
+        int farHost = (hostName == 0 ? 1 : 0);
         PacketHeader outPktHdr, inPktHdr;
         MailHeader outMailHdr, inMailHdr;
-        char *data = "Hello there!";
-        char *ack = "Got it!";
+        char* data = "Hello there!";
+        char* ack = "Got it!";
         char buffer[MaxMailSize];
 
         // construct packet, mail header for original message
         // To: destination machine, mailbox 0
         // From: our machine, reply to: mailbox 1
-        outPktHdr.to = farHost;         
+        outPktHdr.to = farHost;
         outMailHdr.to = 0;
         outMailHdr.from = 1;
         outMailHdr.length = strlen(data) + 1;
 
         // Send the first message
-        postOfficeOut->Send(outPktHdr, outMailHdr, data); 
+        postOfficeOut->Send(outPktHdr, outMailHdr, data);
 
         // Wait for the first message from the other machine
         postOfficeIn->Receive(0, &inPktHdr, &inMailHdr, buffer);
-        cout << "Got: " << buffer << " : from " << inPktHdr.from << ", box " 
-                                                << inMailHdr.from << "\n";
+        cout << "Got: " << buffer << " : from " << inPktHdr.from << ", box "
+            << inMailHdr.from << "\n";
         cout.flush();
 
         // Send acknowledgement to the other machine (using "reply to" mailbox
@@ -240,76 +259,78 @@ Kernel::NetworkTest() {
         outPktHdr.to = inPktHdr.from;
         outMailHdr.to = inMailHdr.from;
         outMailHdr.length = strlen(ack) + 1;
-        postOfficeOut->Send(outPktHdr, outMailHdr, ack); 
+        postOfficeOut->Send(outPktHdr, outMailHdr, ack);
 
         // Wait for the ack from the other machine to the first message we sent
         postOfficeIn->Receive(1, &inPktHdr, &inMailHdr, buffer);
-        cout << "Got: " << buffer << " : from " << inPktHdr.from << ", box " 
-                                                << inMailHdr.from << "\n";
+        cout << "Got: " << buffer << " : from " << inPktHdr.from << ", box "
+            << inMailHdr.from << "\n";
         cout.flush();
     }
 
     // Then we're done!
 }
 
-void ForkExecute(Thread *t)
+void ForkExecute(Thread* t)
 {
-  if (!t->space->Load(t->getName()))
-    return; // executable not found
+    if (!t->space->Load(t->getName())) {
+        return;             // executable not found
+    }
+
+    t->space->Execute(t->getName());
 
-  t->space->Execute(t->getName());
 }
 
 void Kernel::ExecAll()
 {
-	for (int i=1;i<=execfileNum;i++) {
-		int a = Exec(execfile[i]);
-	}
-	currentThread->Finish();
+    for (int i = 1;i <= execfileNum;i++) {
+        int a = Exec(execfile[i], execPriority[i]);
+    }
+    currentThread->Finish();
     //Kernel::Exec();	
 }
 
-
-int Kernel::Exec(char* name)
+// Todo ----
+int Kernel::Exec(char* name, int priority)
 {
-	t[threadNum] = new Thread(name, threadNum);
-	t[threadNum]->space = new AddrSpace();
-	t[threadNum]->Fork((VoidFunctionPtr) &ForkExecute, (void *)t[threadNum]);
+    t[threadNum] = new Thread(name, threadNum);
+    t[threadNum]->setPriority(priority);
+// ---------
+    t[threadNum]->space = new AddrSpace();
+    t[threadNum]->Fork((VoidFunctionPtr)&ForkExecute, (void*)t[threadNum]);
+    threadNum++;
 
-	return threadNum++;
-/*
-    cout << "Total threads number is " << execfileNum << endl;
-    for (int n=1;n<=execfileNum;n++) {
-		t[n] = new Thread(execfile[n]);
-		t[n]->space = new AddrSpace();
-		t[n]->Fork((VoidFunctionPtr) &ForkExecute, (void *)t[n]);
-		cout << "Thread " << execfile[n] << " is executing." << endl;
-	}
-	cout << "debug Kernel::Run finished.\n";	
-*/
-//  Thread *t1 = new Thread(execfile[1]);
-//  Thread *t1 = new Thread("../test/test1");
-//  Thread *t2 = new Thread("../test/test2");
+    return threadNum - 1;
+    /*
+        cout << "Total threads number is " << execfileNum << endl;
+        for (int n=1;n<=execfileNum;n++) {
+            t[n] = new Thread(execfile[n]);
+            t[n]->space = new AddrSpace();
+            t[n]->Fork((VoidFunctionPtr) &ForkExecute, (void *)t[n]);
+            cout << "Thread " << execfile[n] << " is executing." << endl;
+        }
+        cout << "debug Kernel::Run finished.\n";
+    */
+    //  Thread *t1 = new Thread(execfile[1]);
+    //  Thread *t1 = new Thread("../test/test1");
+    //  Thread *t2 = new Thread("../test/test2");
 
-//    AddrSpace *halt = new AddrSpace();
-//  t1->space = new AddrSpace();
-//  t2->space = new AddrSpace();
+    //    AddrSpace *halt = new AddrSpace();
+    //  t1->space = new AddrSpace();
+    //  t2->space = new AddrSpace();
 
-//    halt->Execute("../test/halt");
-//  t1->Fork((VoidFunctionPtr) &ForkExecute, (void *)t1);
-//  t2->Fork((VoidFunctionPtr) &ForkExecute, (void *)t2);
+    //    halt->Execute("../test/halt");
+    //  t1->Fork((VoidFunctionPtr) &ForkExecute, (void *)t1);
+    //  t2->Fork((VoidFunctionPtr) &ForkExecute, (void *)t2);
 
-//	currentThread->Finish();
-//    Kernel::Run();
-//  cout << "after ThreadedKernel:Run();" << endl;  // unreachable
+    //	currentThread->Finish();
+    //    Kernel::Run();
+    //  cout << "after ThreadedKernel:Run();" << endl;  // unreachable
 }
 
-int Kernel::CreateFile(char *filename)
+int Kernel::CreateFile(char* filename)
 {
-	return fileSystem->Create(filename);
+    return fileSystem->Create(filename);
 }
 
-void Kernel::PrintInt(int value)
-{
-    return synchConsoleOut->PutInt(value);
-}
+
diff --git a/code/threads/kernel.h b/code/threads/kernel.h
index 51d3dee..78d1e51 100644
--- a/code/threads/kernel.h
+++ b/code/threads/kernel.h
@@ -25,31 +25,34 @@ class SynchConsoleInput;
 class SynchConsoleOutput;
 class SynchDisk;
 
-
+// Todo ----
+// ---------
 
 class Kernel {
   public:
     Kernel(int argc, char **argv);
-    				// Interpret command line arguments
+    // Interpret command line arguments
     ~Kernel();		        // deallocate the kernel
-    
+
     void Initialize(); 		// initialize the kernel -- separated
-				// from constructor because 
-				// refers to "kernel" as a global
+                          // from constructor because 
+                          // refers to "kernel" as a global
     void ExecAll();
-    int Exec(char* name);
+
+    // Todo ----
+    int Exec(char* name, int priority);
+    // ---------
+
     void ThreadSelfTest();	// self test of threads and synchronization
 
     void ConsoleTest();         // interactive console self test
     void NetworkTest();         // interactive 2-machine network test
-    Thread* getThread(int threadID){return t[threadID];}
+    Thread* getThread(int threadID){return t[threadID];}    
 
-    void PrintInt(int n);    
-    
     int CreateFile(char* filename); // fileSystem call
 
-// These are public for notational convenience; really, 
-// they're global variables used everywhere.
+    // These are public for notational convenience; really, 
+    // they're global variables used everywhere.
 
     Thread *currentThread;	// the thread holding the CPU
     Scheduler *scheduler;	// the ready list
@@ -60,17 +63,21 @@ class Kernel {
     SynchConsoleInput *synchConsoleIn;
     SynchConsoleOutput *synchConsoleOut;
     SynchDisk *synchDisk;
-    FileSystem *fileSystem;
+    FileSystem *fileSystem;     
     PostOfficeInput *postOfficeIn;
     PostOfficeOutput *postOfficeOut;
     FrameTable *frameTable;
-
     int hostName;               // machine identifier
 
   private:
 
     Thread* t[10];
+
+    // Todo ----
     char*   execfile[10];
+    int execPriority[10];
+    // ---------
+
     int execfileNum;
     int threadNum;
     bool randomSlice;		// enable pseudo-random time slicing
@@ -85,5 +92,3 @@ class Kernel {
 
 
 #endif // KERNEL_H
-
-
diff --git a/code/threads/main.cc b/code/threads/main.cc
index 093b7d3..ead7707 100644
--- a/code/threads/main.cc
+++ b/code/threads/main.cc
@@ -47,8 +47,8 @@
 #include "sysdep.h"
 
 // global variables
-Kernel *kernel;
-Debug *debug;
+Kernel* kernel;
+Debug* debug;
 
 
 //----------------------------------------------------------------------
@@ -56,11 +56,11 @@ Debug *debug;
 //	Delete kernel data structures; called when user hits "ctl-C".
 //----------------------------------------------------------------------
 
-static void 
-Cleanup(int x) 
-{     
+static void
+Cleanup(int x)
+{
     cerr << "\nCleaning up after signal " << x << "\n";
-    delete kernel; 
+    delete kernel;
 }
 
 //-------------------------------------------------------------------
@@ -78,42 +78,42 @@ static const int TransferSize = 128;
 //----------------------------------------------------------------------
 
 static void
-Copy(char *from, char *to)
+Copy(char* from, char* to)
 {
     int fd;
     OpenFile* openFile;
     int amountRead, fileLength;
-    char *buffer;
+    char* buffer;
 
-// Open UNIX file
-    if ((fd = OpenForReadWrite(from,FALSE)) < 0) {       
+    // Open UNIX file
+    if ((fd = OpenForReadWrite(from, FALSE)) < 0) {
         printf("Copy: couldn't open input file %s\n", from);
         return;
     }
 
-// Figure out length of UNIX file
-    Lseek(fd, 0, 2);            
+    // Figure out length of UNIX file
+    Lseek(fd, 0, 2);
     fileLength = Tell(fd);
     Lseek(fd, 0, 0);
 
-// Create a Nachos file of the same length
-    DEBUG('f', "Copying file " << from << " of size " << fileLength <<  " to file " << to);
+    // Create a Nachos file of the same length
+    DEBUG('f', "Copying file " << from << " of size " << fileLength << " to file " << to);
     if (!kernel->fileSystem->Create(to, fileLength)) {   // Create Nachos file
         printf("Copy: couldn't create output file %s\n", to);
         Close(fd);
         return;
     }
-    
+
     openFile = kernel->fileSystem->Open(to);
     ASSERT(openFile != NULL);
-    
-// Copy the data in TransferSize chunks
-    buffer = new char[TransferSize];
-    while ((amountRead=ReadPartial(fd, buffer, sizeof(char)*TransferSize)) > 0)
-        openFile->Write(buffer, amountRead);    
-    delete [] buffer;
 
-// Close the UNIX and the Nachos files
+    // Copy the data in TransferSize chunks
+    buffer = new char[TransferSize];
+    while ((amountRead = ReadPartial(fd, buffer, sizeof(char) * TransferSize)) > 0)
+        openFile->Write(buffer, amountRead);
+    delete[] buffer;
+
+    // Close the UNIX and the Nachos files
     delete openFile;
     Close(fd);
 }
@@ -126,22 +126,22 @@ Copy(char *from, char *to)
 //----------------------------------------------------------------------
 
 void
-Print(char *name)
+Print(char* name)
 {
-    OpenFile *openFile;    
+    OpenFile* openFile;
     int i, amountRead;
-    char *buffer;
+    char* buffer;
 
     if ((openFile = kernel->fileSystem->Open(name)) == NULL) {
         printf("Print: unable to open file %s\n", name);
         return;
     }
-    
+
     buffer = new char[TransferSize];
     while ((amountRead = openFile->Read(buffer, TransferSize)) > 0)
         for (i = 0; i < amountRead; i++)
             printf("%c", buffer[i]);
-    delete [] buffer;
+    delete[] buffer;
 
     delete openFile;            // close the Nachos file
     return;
@@ -164,19 +164,19 @@ Print(char *name)
 //----------------------------------------------------------------------
 
 int
-main(int argc, char **argv)
+main(int argc, char** argv)
 {
     int i;
-    char *debugArg = "";
-    char *userProgName = NULL;        // default is not to execute a user prog
+    char* debugArg = "";
+    char* userProgName = NULL;        // default is not to execute a user prog
     bool threadTestFlag = false;
     bool consoleTestFlag = false;
     bool networkTestFlag = false;
 #ifndef FILESYS_STUB
-    char *copyUnixFileName = NULL;    // UNIX file to be copied into Nachos
-    char *copyNachosFileName = NULL;  // name of copied file in Nachos
-    char *printFileName = NULL; 
-    char *removeFileName = NULL;
+    char* copyUnixFileName = NULL;    // UNIX file to be copied into Nachos
+    char* copyNachosFileName = NULL;  // name of copied file in Nachos
+    char* printFileName = NULL;
+    char* removeFileName = NULL;
     bool dirListFlag = false;
     bool dumpFlag = false;
 #endif //FILESYS_STUB
@@ -186,65 +186,65 @@ main(int argc, char **argv)
     // the Kernel constructor
     for (i = 1; i < argc; i++) {
         if (strcmp(argv[i], "-d") == 0) {
-	    ASSERT(i + 1 < argc);   // next argument is debug string
+            ASSERT(i + 1 < argc);   // next argument is debug string
             debugArg = argv[i + 1];
-	    i++;
-	}
-	else if (strcmp(argv[i], "-z") == 0) {
+            i++;
+        }
+        else if (strcmp(argv[i], "-z") == 0) {
             cout << copyright << "\n";
-	}
-	else if (strcmp(argv[i], "-x") == 0) {
-	    ASSERT(i + 1 < argc);
-	    userProgName = argv[i + 1];
-	    i++;
-	}
-	else if (strcmp(argv[i], "-K") == 0) {
-	    threadTestFlag = TRUE;
-	}
-	else if (strcmp(argv[i], "-C") == 0) {
-	    consoleTestFlag = TRUE;
-	}
-	else if (strcmp(argv[i], "-N") == 0) {
-	    networkTestFlag = TRUE;
-	}
+        }
+        else if (strcmp(argv[i], "-x") == 0) {
+            ASSERT(i + 1 < argc);
+            userProgName = argv[i + 1];
+            i++;
+        }
+        else if (strcmp(argv[i], "-K") == 0) {
+            threadTestFlag = TRUE;
+        }
+        else if (strcmp(argv[i], "-C") == 0) {
+            consoleTestFlag = TRUE;
+        }
+        else if (strcmp(argv[i], "-N") == 0) {
+            networkTestFlag = TRUE;
+        }
 #ifndef FILESYS_STUB
-	else if (strcmp(argv[i], "-cp") == 0) {
-	    ASSERT(i + 2 < argc);
-	    copyUnixFileName = argv[i + 1];
-	    copyNachosFileName = argv[i + 2];
-	    i += 2;
-	}
-	else if (strcmp(argv[i], "-p") == 0) {
-	    ASSERT(i + 1 < argc);
-	    printFileName = argv[i + 1];
-	    i++;
-	}
-	else if (strcmp(argv[i], "-r") == 0) {
-	    ASSERT(i + 1 < argc);
-	    removeFileName = argv[i + 1];
-	    i++;
-	}
-	else if (strcmp(argv[i], "-l") == 0) {
-	    dirListFlag = true;
-	}
-	else if (strcmp(argv[i], "-D") == 0) {
-	    dumpFlag = true;
-	}
+        else if (strcmp(argv[i], "-cp") == 0) {
+            ASSERT(i + 2 < argc);
+            copyUnixFileName = argv[i + 1];
+            copyNachosFileName = argv[i + 2];
+            i += 2;
+        }
+        else if (strcmp(argv[i], "-p") == 0) {
+            ASSERT(i + 1 < argc);
+            printFileName = argv[i + 1];
+            i++;
+        }
+        else if (strcmp(argv[i], "-r") == 0) {
+            ASSERT(i + 1 < argc);
+            removeFileName = argv[i + 1];
+            i++;
+        }
+        else if (strcmp(argv[i], "-l") == 0) {
+            dirListFlag = true;
+        }
+        else if (strcmp(argv[i], "-D") == 0) {
+            dumpFlag = true;
+        }
 #endif //FILESYS_STUB
-	else if (strcmp(argv[i], "-u") == 0) {
+        else if (strcmp(argv[i], "-u") == 0) {
             cout << "Partial usage: nachos [-z -d debugFlags]\n";
             cout << "Partial usage: nachos [-x programName]\n";
-	    cout << "Partial usage: nachos [-K] [-C] [-N]\n";
+            cout << "Partial usage: nachos [-K] [-C] [-N]\n";
 #ifndef FILESYS_STUB
             cout << "Partial usage: nachos [-cp UnixFile NachosFile]\n";
             cout << "Partial usage: nachos [-p fileName] [-r fileName]\n";
             cout << "Partial usage: nachos [-l] [-D]\n";
 #endif //FILESYS_STUB
-	}
+        }
 
     }
     debug = new Debug(debugArg);
-    
+
     DEBUG(dbgThread, "Entering main");
 
     kernel = new Kernel(argc, argv);
@@ -256,42 +256,42 @@ main(int argc, char **argv)
     // at this point, the kernel is ready to do something
     // run some tests, if requested
     if (threadTestFlag) {
-      kernel->ThreadSelfTest();  // test threads and synchronization
+        kernel->ThreadSelfTest();  // test threads and synchronization
     }
     if (consoleTestFlag) {
-      kernel->ConsoleTest();   // interactive test of the synchronized console
+        kernel->ConsoleTest();   // interactive test of the synchronized console
     }
     if (networkTestFlag) {
-      kernel->NetworkTest();   // two-machine test of the network
+        kernel->NetworkTest();   // two-machine test of the network
     }
 
 #ifndef FILESYS_STUB
     if (removeFileName != NULL) {
-      kernel->fileSystem->Remove(removeFileName);
+        kernel->fileSystem->Remove(removeFileName);
     }
     if (copyUnixFileName != NULL && copyNachosFileName != NULL) {
-      Copy(copyUnixFileName,copyNachosFileName);
+        Copy(copyUnixFileName, copyNachosFileName);
     }
     if (dumpFlag) {
-      kernel->fileSystem->Print();
+        kernel->fileSystem->Print();
     }
     if (dirListFlag) {
-      kernel->fileSystem->List();
+        kernel->fileSystem->List();
     }
     if (printFileName != NULL) {
-      Print(printFileName);
+        Print(printFileName);
     }
 #endif // FILESYS_STUB
 
     // finally, run an initial user program if requested to do so
 
-		kernel->ExecAll();
+    kernel->ExecAll();
     // If we don't run a user program, we may get here.
     // Calling "return" would terminate the program.
     // Instead, call Halt, which will first clean up, then
     //  terminate.
 //    kernel->interrupt->Halt();
-    
+
     ASSERTNOTREACHED();
 }
 
diff --git a/code/threads/scheduler.cc b/code/threads/scheduler.cc
index 11278b9..6c305b6 100644
--- a/code/threads/scheduler.cc
+++ b/code/threads/scheduler.cc
@@ -22,6 +22,7 @@
 #include "debug.h"
 #include "scheduler.h"
 #include "main.h"
+#include <functional>
 
 //----------------------------------------------------------------------
 // Scheduler::Scheduler
@@ -29,11 +30,22 @@
 //	Initially, no ready threads.
 //----------------------------------------------------------------------
 
+// Todo ----
+
+int cmp(Thread *a, Thread *b)
+{
+  int ap = a->getPriority();
+  int bp = b->getPriority();
+  return (ap < bp) - (ap > bp);
+}
+
 Scheduler::Scheduler()
-{ 
-    readyList = new List<Thread *>; 
-    toBeDestroyed = NULL;
-} 
+{
+  readyList = new SortedList(cmp);
+// ---------
+
+  toBeDestroyed = NULL;
+}
 
 //----------------------------------------------------------------------
 // Scheduler::~Scheduler
@@ -41,9 +53,9 @@ Scheduler::Scheduler()
 //----------------------------------------------------------------------
 
 Scheduler::~Scheduler()
-{ 
-    delete readyList; 
-} 
+{
+  delete readyList;
+}
 
 //----------------------------------------------------------------------
 // Scheduler::ReadyToRun
@@ -54,13 +66,15 @@ Scheduler::~Scheduler()
 //----------------------------------------------------------------------
 
 void
-Scheduler::ReadyToRun (Thread *thread)
+Scheduler::ReadyToRun(Thread* thread)
 {
-    ASSERT(kernel->interrupt->getLevel() == IntOff);
-    DEBUG(dbgThread, "Putting thread on ready list: " << thread->getName());
-	//cout << "Putting thread on ready list: " << thread->getName() << endl ;
-    thread->setStatus(READY);
-    readyList->Append(thread);
+  ASSERT(kernel->interrupt->getLevel() == IntOff);
+  DEBUG(dbgThread, "Putting thread on ready list: " << thread->getName());
+  //cout << "Putting thread on ready list: " << thread->getName() << endl ;
+  thread->setStatus(READY);
+
+  DEBUG(dbgSche, "[A] Tick [" << kernel->stats->totalTicks << "]: Process [" << thread->getName() << "] is inserted into queue.");
+  readyList->Insert(thread);
 }
 
 //----------------------------------------------------------------------
@@ -71,14 +85,16 @@ Scheduler::ReadyToRun (Thread *thread)
 //	Thread is removed from the ready list.
 //----------------------------------------------------------------------
 
-Thread *
-Scheduler::FindNextToRun ()
+Thread*
+Scheduler::FindNextToRun()
 {
   ASSERT(kernel->interrupt->getLevel() == IntOff);
 
   if (readyList->IsEmpty()) {
     return NULL;
-  } else {
+  }
+  else {
+    DEBUG(dbgSche, "[B] Tick [" << kernel->stats->totalTicks << "]: Process [" << readyList->Front()->getName() << "] is removed from queue.");
     return readyList->RemoveFront();
   }
 }
@@ -101,9 +117,9 @@ Scheduler::FindNextToRun ()
 //----------------------------------------------------------------------
 
 void
-Scheduler::Run (Thread *nextThread, bool finishing)
+Scheduler::Run(Thread* nextThread, bool finishing)
 {
-  Thread *oldThread = kernel->currentThread;
+  Thread* oldThread = kernel->currentThread;
 
   ASSERT(kernel->interrupt->getLevel() == IntOff);
 
@@ -124,6 +140,7 @@ Scheduler::Run (Thread *nextThread, bool finishing)
   nextThread->setStatus(RUNNING);      // nextThread is now running
 
   DEBUG(dbgThread, "Switching from: " << oldThread->getName() << " to: " << nextThread->getName());
+  DEBUG(dbgSche, "[C] Tick [" << kernel->stats->totalTicks << "]: Process [" << nextThread->getName() << "] is now selected for execution, thread [" << oldThread->getName() << "] is replaced.");
 
   // This is a machine-dependent assembly language routine defined 
   // in switch.s.  You may have to think
@@ -165,7 +182,7 @@ Scheduler::CheckToBeDestroyed()
     toBeDestroyed = NULL;
   }
 }
- 
+
 //----------------------------------------------------------------------
 // Scheduler::Print
 // 	Print the scheduler state -- in other words, the contents of
@@ -174,6 +191,6 @@ Scheduler::CheckToBeDestroyed()
 void
 Scheduler::Print()
 {
-    cout << "Ready list contents:\n";
-    readyList->Apply(ThreadPrint);
+  cout << "Ready list contents:\n";
+  readyList->Apply(ThreadPrint);
 }
diff --git a/code/threads/scheduler.h b/code/threads/scheduler.h
index 36964d6..c78cc18 100644
--- a/code/threads/scheduler.h
+++ b/code/threads/scheduler.h
@@ -23,22 +23,25 @@ class Scheduler {
     ~Scheduler();		// De-allocate ready list
 
     void ReadyToRun(Thread* thread);	
-    				// Thread can be dispatched.
+    // Thread can be dispatched.
     Thread* FindNextToRun();	// Dequeue first thread on the ready 
-				// list, if any, and return thread.
+                              // list, if any, and return thread.
     void Run(Thread* nextThread, bool finishing);
-    				// Cause nextThread to start running
+    // Cause nextThread to start running
     void CheckToBeDestroyed();// Check if thread that had been
-    				// running needs to be deleted
+                              // running needs to be deleted
     void Print();		// Print contents of ready list
-    
+
     // SelfTest for scheduler is implemented in class Thread
     
   private:
-    List<Thread *> *readyList;  // queue of threads that are ready to run,
-				// but not running
+    // Todo ----
+    SortedList<Thread *> *readyList;  // queue of threads that are ready to run,
+                                      // but not running
+    // ---------
+
     Thread *toBeDestroyed;	// finishing thread to be destroyed
-    				// by the next thread that runs
+                            // by the next thread that runs
 };
 
 #endif // SCHEDULER_H
diff --git a/code/threads/synch.cc b/code/threads/synch.cc
index 5be111c..f62f2db 100644
--- a/code/threads/synch.cc
+++ b/code/threads/synch.cc
@@ -48,7 +48,7 @@ Semaphore::Semaphore(char* debugName, int initialValue)
 {
     name = debugName;
     value = initialValue;
-    queue = new List<Thread *>;
+    queue = new List<Thread*>;
 }
 
 //----------------------------------------------------------------------
@@ -75,20 +75,20 @@ Semaphore::~Semaphore()
 void
 Semaphore::P()
 {
-    Interrupt *interrupt = kernel->interrupt;
-    Thread *currentThread = kernel->currentThread;
-    
+    Interrupt* interrupt = kernel->interrupt;
+    Thread* currentThread = kernel->currentThread;
+
     // disable interrupts
-    IntStatus oldLevel = interrupt->SetLevel(IntOff);	
-    
+    IntStatus oldLevel = interrupt->SetLevel(IntOff);
+
     while (value == 0) { 		// semaphore not available
-	queue->Append(currentThread);	// so go to sleep
-	currentThread->Sleep(FALSE);
-    } 
+        queue->Append(currentThread);	// so go to sleep
+        currentThread->Sleep(FALSE);
+    }
     value--; 			// semaphore available, consume its value
-   
+
     // re-enable interrupts
-    (void) interrupt->SetLevel(oldLevel);	
+    (void)interrupt->SetLevel(oldLevel);
 }
 
 //----------------------------------------------------------------------
@@ -102,18 +102,18 @@ Semaphore::P()
 void
 Semaphore::V()
 {
-    Interrupt *interrupt = kernel->interrupt;
-    
+    Interrupt* interrupt = kernel->interrupt;
+
     // disable interrupts
-    IntStatus oldLevel = interrupt->SetLevel(IntOff);	
-    
+    IntStatus oldLevel = interrupt->SetLevel(IntOff);
+
     if (!queue->IsEmpty()) {  // make thread ready.
-	kernel->scheduler->ReadyToRun(queue->RemoveFront());
+        kernel->scheduler->ReadyToRun(queue->RemoveFront());
     }
     value++;
-    
+
     // re-enable interrupts
-    (void) interrupt->SetLevel(oldLevel);
+    (void)interrupt->SetLevel(oldLevel);
 }
 
 //----------------------------------------------------------------------
@@ -122,27 +122,27 @@ Semaphore::V()
 //	to control two threads ping-ponging back and forth.
 //----------------------------------------------------------------------
 
-static Semaphore *ping;
+static Semaphore* ping;
 static void
-SelfTestHelper (Semaphore *pong) 
+SelfTestHelper(Semaphore* pong)
 {
     for (int i = 0; i < 10; i++) {
         ping->P();
-	pong->V();
+        pong->V();
     }
 }
 
 void
 Semaphore::SelfTest()
 {
-    Thread *helper = new Thread("ping", 1);
+    Thread* helper = new Thread("ping", 1);
 
     ASSERT(value == 0);		// otherwise test won't work!
     ping = new Semaphore("ping", 0);
-    helper->Fork((VoidFunctionPtr) SelfTestHelper, this);
+    helper->Fork((VoidFunctionPtr)SelfTestHelper, this);
     for (int i = 0; i < 10; i++) {
         ping->V();
-	this->P();
+        this->P();
     }
     delete ping;
 }
@@ -213,7 +213,7 @@ void Lock::Release()
 Condition::Condition(char* debugName)
 {
     name = debugName;
-    waitQueue = new List<Semaphore *>;
+    waitQueue = new List<Semaphore*>;
 }
 
 //----------------------------------------------------------------------
@@ -241,18 +241,18 @@ Condition::~Condition()
 //	"conditionLock" -- lock protecting the use of this condition
 //----------------------------------------------------------------------
 
-void Condition::Wait(Lock* conditionLock) 
+void Condition::Wait(Lock* conditionLock)
 {
-     Semaphore *waiter;
-    
-     ASSERT(conditionLock->IsHeldByCurrentThread());
+    Semaphore* waiter;
 
-     waiter = new Semaphore("condition", 0);
-     waitQueue->Append(waiter);
-     conditionLock->Release();
-     waiter->P();
-     conditionLock->Acquire();
-     delete waiter;
+    ASSERT(conditionLock->IsHeldByCurrentThread());
+
+    waiter = new Semaphore("condition", 0);
+    waitQueue->Append(waiter);
+    conditionLock->Release();
+    waiter->P();
+    conditionLock->Acquire();
+    delete waiter;
 }
 
 //----------------------------------------------------------------------
@@ -272,13 +272,13 @@ void Condition::Wait(Lock* conditionLock)
 
 void Condition::Signal(Lock* conditionLock)
 {
-    Semaphore *waiter;
-    
+    Semaphore* waiter;
+
     ASSERT(conditionLock->IsHeldByCurrentThread());
-    
+
     if (!waitQueue->IsEmpty()) {
         waiter = waitQueue->RemoveFront();
-	waiter->V();
+        waiter->V();
     }
 }
 
@@ -289,7 +289,7 @@ void Condition::Signal(Lock* conditionLock)
 //	"conditionLock" -- lock protecting the use of this condition
 //----------------------------------------------------------------------
 
-void Condition::Broadcast(Lock* conditionLock) 
+void Condition::Broadcast(Lock* conditionLock)
 {
     while (!waitQueue->IsEmpty()) {
         Signal(conditionLock);
diff --git a/code/threads/thread.cc b/code/threads/thread.cc
index 8bae3ad..87a24f1 100644
--- a/code/threads/thread.cc
+++ b/code/threads/thread.cc
@@ -1,4 +1,4 @@
-// thread.cc 
+// thread.cc
 //	Routines to manage threads.  These are the main operations:
 //
 //	Fork -- create a thread to run a procedure concurrently
@@ -9,11 +9,11 @@
 //	Finish -- called when the forked procedure finishes, to clean up
 //	Yield -- relinquish control over the CPU to another ready thread
 //	Sleep -- relinquish control over the CPU, but thread is now blocked.
-//		In other words, it will not run again, until explicitly 
+//		In other words, it will not run again, until explicitly
 //		put back on the ready queue.
 //
 // Copyright (c) 1992-1996 The Regents of the University of California.
-// All rights reserved.  See copyright.h for copyright notice and limitation 
+// All rights reserved.  See copyright.h for copyright notice and limitation
 // of liability and disclaimer of warranty provisions.
 
 #include "copyright.h"
@@ -33,19 +33,20 @@ const int STACK_FENCEPOST = 0xdedbeef;
 //	"threadName" is an arbitrary string, useful for debugging.
 //----------------------------------------------------------------------
 
-Thread::Thread(char* threadName, int threadID)
+Thread::Thread(char *threadName, int threadID)
 {
-  ID = threadID;
-  name = threadName;
-  stackTop = NULL;
-  stack = NULL;
-  status = JUST_CREATED;
-  for (int i = 0; i < MachineStateSize; i++) {
-    machineState[i] = NULL;		// not strictly necessary, since
-                              // new thread ignores contents 
-                              // of machine registers
-  }
-  space = NULL;
+    ID = threadID;
+    name = threadName;
+    stackTop = NULL;
+    stack = NULL;
+    status = JUST_CREATED;
+    for (int i = 0; i < MachineStateSize; i++)
+    {
+        machineState[i] = NULL; // not strictly necessary, since
+                                // new thread ignores contents
+                                // of machine registers
+    }
+    space = NULL;
 }
 
 //----------------------------------------------------------------------
@@ -62,15 +63,15 @@ Thread::Thread(char* threadName, int threadID)
 
 Thread::~Thread()
 {
-  DEBUG(dbgThread, "Deleting thread: " << name);
-  ASSERT(this != kernel->currentThread);
-  if (stack != NULL)
-    DeallocBoundedArray((char *) stack, StackSize * sizeof(int));
+    DEBUG(dbgThread, "Deleting thread: " << name);
+    ASSERT(this != kernel->currentThread);
+    if (stack != NULL)
+        DeallocBoundedArray((char *)stack, StackSize * sizeof(int));
 }
 
 //----------------------------------------------------------------------
 // Thread::Fork
-// 	Invoke (*func)(arg), allowing caller and callee to execute 
+// 	Invoke (*func)(arg), allowing caller and callee to execute
 //	concurrently.
 //
 //	NOTE: although our definition allows only a single argument
@@ -83,26 +84,25 @@ Thread::~Thread()
 //		2. Initialize the stack so that a call to SWITCH will
 //		cause it to run the procedure
 //		3. Put the thread on the ready queue
-// 	
+//
 //	"func" is the procedure to run concurrently.
 //	"arg" is a single argument to be passed to the procedure.
 //----------------------------------------------------------------------
 
-void 
-Thread::Fork(VoidFunctionPtr func, void *arg)
+void Thread::Fork(VoidFunctionPtr func, void *arg)
 {
-  Interrupt *interrupt = kernel->interrupt;
-  Scheduler *scheduler = kernel->scheduler;
-  IntStatus oldLevel;
+    Interrupt *interrupt = kernel->interrupt;
+    Scheduler *scheduler = kernel->scheduler;
+    IntStatus oldLevel;
 
-  DEBUG(dbgThread, "Forking thread: " << name << " f(a): " << (int) func << " " << arg);
-  StackAllocate(func, arg);
+    DEBUG(dbgThread, "Forking thread: " << name << " f(a): " << (int)func << " " << arg);
+    StackAllocate(func, arg);
 
-  oldLevel = interrupt->SetLevel(IntOff);
-  scheduler->ReadyToRun(this);	// ReadyToRun assumes that interrupts 
-                                // are disabled!
-  (void) interrupt->SetLevel(oldLevel);
-}    
+    oldLevel = interrupt->SetLevel(IntOff);
+    scheduler->ReadyToRun(this); // ReadyToRun assumes that interrupts
+                                 // are disabled!
+    (void)interrupt->SetLevel(oldLevel);
+}
 
 //----------------------------------------------------------------------
 // Thread::CheckOverflow
@@ -119,16 +119,16 @@ Thread::Fork(VoidFunctionPtr func, void *arg)
 // 	Don't do this: void foo() { int bigArray[10000]; ... }
 //----------------------------------------------------------------------
 
-void
-Thread::CheckOverflow()
+void Thread::CheckOverflow()
 {
-  if (stack != NULL) {
-#ifdef HPUX			// Stacks grow upward on the Snakes
-    ASSERT(stack[StackSize - 1] == STACK_FENCEPOST);
+    if (stack != NULL)
+    {
+#ifdef HPUX // Stacks grow upward on the Snakes
+        ASSERT(stack[StackSize - 1] == STACK_FENCEPOST);
 #else
-    ASSERT(*stack == STACK_FENCEPOST);
+        ASSERT(*stack == STACK_FENCEPOST);
 #endif
-  }
+    }
 }
 
 //----------------------------------------------------------------------
@@ -137,28 +137,27 @@ Thread::CheckOverflow()
 //	executing the forked procedure.
 //
 // 	It's main responsibilities are:
-//	1. deallocate the previously running thread if it finished 
+//	1. deallocate the previously running thread if it finished
 //		(see Thread::Finish())
 //	2. enable interrupts (so we can get time-sliced)
 //----------------------------------------------------------------------
 
-void
-Thread::Begin ()
+void Thread::Begin()
 {
     ASSERT(this == kernel->currentThread);
     DEBUG(dbgThread, "Beginning thread: " << name);
-    
+
     kernel->scheduler->CheckToBeDestroyed();
     kernel->interrupt->Enable();
 }
 
 //----------------------------------------------------------------------
 // Thread::Finish
-// 	Called by ThreadRoot when a thread is done executing the 
+// 	Called by ThreadRoot when a thread is done executing the
 //	forked procedure.
 //
-// 	NOTE: we can't immediately de-allocate the thread data structure 
-//	or the execution stack, because we're still running in the thread 
+// 	NOTE: we can't immediately de-allocate the thread data structure
+//	or the execution stack, because we're still running in the thread
 //	and we're still on the stack!  Instead, we tell the scheduler
 //	to call the destructor, once it is running in the context of a different thread.
 //
@@ -167,18 +166,16 @@ Thread::Begin ()
 //----------------------------------------------------------------------
 
 //
-void
-Thread::Finish ()
+void Thread::Finish()
 {
-  (void) kernel->interrupt->SetLevel(IntOff);		
-  ASSERT(this == kernel->currentThread);
+    (void)kernel->interrupt->SetLevel(IntOff);
+    ASSERT(this == kernel->currentThread);
 
-  DEBUG(dbgThread, "Finishing thread: " << name);
-  Sleep(TRUE);				// invokes SWITCH
-                      // not reached
+    DEBUG(dbgThread, "Finishing thread: " << name);
+    Sleep(TRUE); // invokes SWITCH
+    // not reached
 }
 
-
 //----------------------------------------------------------------------
 // Thread::Yield
 // 	Relinquish the CPU if any other thread is ready to run.
@@ -192,33 +189,33 @@ Thread::Finish ()
 //	NOTE: we disable interrupts, so that looking at the thread
 //	on the front of the ready list, and switching to it, can be done
 //	atomically.  On return, we re-set the interrupt level to its
-//	original state, in case we are called with interrupts disabled. 
+//	original state, in case we are called with interrupts disabled.
 //
 // 	Similar to Thread::Sleep(), but a little different.
 //----------------------------------------------------------------------
 
-void
-Thread::Yield ()
+void Thread::Yield()
 {
-  Thread *nextThread;
-  IntStatus oldLevel = kernel->interrupt->SetLevel(IntOff);
+    Thread *nextThread;
+    IntStatus oldLevel = kernel->interrupt->SetLevel(IntOff);
 
-  ASSERT(this == kernel->currentThread);
+    ASSERT(this == kernel->currentThread);
 
-  DEBUG(dbgThread, "Yielding thread: " << name);
+    DEBUG(dbgThread, "Yielding thread: " << name);
 
-  nextThread = kernel->scheduler->FindNextToRun();
-  if (nextThread != NULL) {
-    kernel->scheduler->ReadyToRun(this);
-    kernel->scheduler->Run(nextThread, FALSE);
-  }
-  (void) kernel->interrupt->SetLevel(oldLevel);
+    nextThread = kernel->scheduler->FindNextToRun();
+    if (nextThread != NULL)
+    {
+        kernel->scheduler->ReadyToRun(this);
+        kernel->scheduler->Run(nextThread, FALSE);
+    }
+    (void)kernel->interrupt->SetLevel(oldLevel);
 }
 
 //----------------------------------------------------------------------
 // Thread::Sleep
 // 	Relinquish the CPU, because the current thread has either
-//	finished or is blocked waiting on a synchronization 
+//	finished or is blocked waiting on a synchronization
 //	variable (Semaphore, Lock, or Condition).  In the latter case,
 //	eventually some thread will wake this thread up, and put it
 //	back on the ready queue, so that it can be re-scheduled.
@@ -231,34 +228,34 @@ Thread::Yield ()
 //
 //	NOTE: we assume interrupts are already disabled, because it
 //	is called from the synchronization routines which must
-//	disable interrupts for atomicity.   We need interrupts off 
+//	disable interrupts for atomicity.   We need interrupts off
 //	so that there can't be a time slice between pulling the first thread
 //	off the ready list, and switching to it.
 //----------------------------------------------------------------------
-void
-Thread::Sleep (bool finishing)
+void Thread::Sleep(bool finishing)
 {
-  Thread *nextThread;
+    Thread *nextThread;
 
-  ASSERT(this == kernel->currentThread);
-  ASSERT(kernel->interrupt->getLevel() == IntOff);
+    ASSERT(this == kernel->currentThread);
+    ASSERT(kernel->interrupt->getLevel() == IntOff);
 
-  DEBUG(dbgThread, "Sleeping thread: " << name);
+    DEBUG(dbgThread, "Sleeping thread: " << name);
 
-  status = BLOCKED;
-  //cout << "debug Thread::Sleep " << name << "wait for Idle\n";
-  while ((nextThread = kernel->scheduler->FindNextToRun()) == NULL) {
-    kernel->interrupt->Idle();	// no one to run, wait for an interrupt
-  }    
-  // returns when it's time for us to run
-  kernel->scheduler->Run(nextThread, finishing); 
+    status = BLOCKED;
+    // cout << "debug Thread::Sleep " << name << "wait for Idle\n";
+    while ((nextThread = kernel->scheduler->FindNextToRun()) == NULL)
+    {
+        kernel->interrupt->Idle(); // no one to run, wait for an interrupt
+    }
+    // returns when it's time for us to run
+    kernel->scheduler->Run(nextThread, finishing);
 }
 
 //----------------------------------------------------------------------
 // ThreadBegin, ThreadFinish,  ThreadPrint
 //	Dummy functions because C++ does not (easily) allow pointers to member
 //	functions.  So we create a dummy C function
-//	(which we can pass a pointer to), that then simply calls the 
+//	(which we can pass a pointer to), that then simply calls the
 //	member function.
 //----------------------------------------------------------------------
 
@@ -277,16 +274,19 @@ void ThreadPrint(Thread *t) { t->Print(); }
 static void *
 PLabelToAddr(void *plabel)
 {
-  int funcPtr = (int) plabel;
+    int funcPtr = (int)plabel;
 
-  if (funcPtr & 0x02) {
-    // L-Field is set.  This is a PLT pointer
-    funcPtr -= 2;	// Get rid of the L bit
-    return (*(void **)funcPtr);
-  } else {
-    // L-field not set.
-    return plabel;
-  }
+    if (funcPtr & 0x02)
+    {
+        // L-Field is set.  This is a PLT pointer
+        funcPtr -= 2; // Get rid of the L bit
+        return (*(void **)funcPtr);
+    }
+    else
+    {
+        // L-field not set.
+        return plabel;
+    }
 }
 #endif
 
@@ -302,62 +302,60 @@ PLabelToAddr(void *plabel)
 //	"arg" is the parameter to be passed to the procedure
 //----------------------------------------------------------------------
 
-void
-Thread::StackAllocate (VoidFunctionPtr func, void *arg)
+void Thread::StackAllocate(VoidFunctionPtr func, void *arg)
 {
-  stack = (int *) AllocBoundedArray(StackSize * sizeof(int));
+    stack = (int *)AllocBoundedArray(StackSize * sizeof(int));
 
 #ifdef PARISC
-  // HP stack works from low addresses to high addresses
-  // everyone else works the other way: from high addresses to low addresses
-  stackTop = stack + 16;	// HP requires 64-byte frame marker
-  stack[StackSize - 1] = STACK_FENCEPOST;
+    // HP stack works from low addresses to high addresses
+    // everyone else works the other way: from high addresses to low addresses
+    stackTop = stack + 16; // HP requires 64-byte frame marker
+    stack[StackSize - 1] = STACK_FENCEPOST;
 #endif
 
 #ifdef SPARC
-  stackTop = stack + StackSize - 96; 	// SPARC stack must contains at 
-                                      // least 1 activation record 
-                                      // to start with.
-  *stack = STACK_FENCEPOST;
-#endif 
+    stackTop = stack + StackSize - 96; // SPARC stack must contains at
+                                       // least 1 activation record
+                                       // to start with.
+    *stack = STACK_FENCEPOST;
+#endif
 
-#ifdef PowerPC // RS6000
-  stackTop = stack + StackSize - 16; 	// RS6000 requires 64-byte frame marker
-  *stack = STACK_FENCEPOST;
-#endif 
+#ifdef PowerPC                         // RS6000
+    stackTop = stack + StackSize - 16; // RS6000 requires 64-byte frame marker
+    *stack = STACK_FENCEPOST;
+#endif
 
 #ifdef DECMIPS
-  stackTop = stack + StackSize - 4;	// -4 to be on the safe side!
-  *stack = STACK_FENCEPOST;
+    stackTop = stack + StackSize - 4; // -4 to be on the safe side!
+    *stack = STACK_FENCEPOST;
 #endif
 
 #ifdef ALPHA
-  stackTop = stack + StackSize - 8;	// -8 to be on the safe side!
-  *stack = STACK_FENCEPOST;
+    stackTop = stack + StackSize - 8; // -8 to be on the safe side!
+    *stack = STACK_FENCEPOST;
 #endif
 
-
 #ifdef x86
-  // the x86 passes the return address on the stack.  In order for SWITCH() 
-  // to go to ThreadRoot when we switch to this thread, the return addres 
-  // used in SWITCH() must be the starting address of ThreadRoot.
-  stackTop = stack + StackSize - 4;	// -4 to be on the safe side!
-  *(--stackTop) = (int) ThreadRoot;
-  *stack = STACK_FENCEPOST;
+    // the x86 passes the return address on the stack.  In order for SWITCH()
+    // to go to ThreadRoot when we switch to this thread, the return addres
+    // used in SWITCH() must be the starting address of ThreadRoot.
+    stackTop = stack + StackSize - 4; // -4 to be on the safe side!
+    *(--stackTop) = (int)ThreadRoot;
+    *stack = STACK_FENCEPOST;
 #endif
 
 #ifdef PARISC
-  machineState[PCState] = PLabelToAddr(ThreadRoot);
-  machineState[StartupPCState] = PLabelToAddr(ThreadBegin);
-  machineState[InitialPCState] = PLabelToAddr(func);
-  machineState[InitialArgState] = arg;
-  machineState[WhenDonePCState] = PLabelToAddr(ThreadFinish);
+    machineState[PCState] = PLabelToAddr(ThreadRoot);
+    machineState[StartupPCState] = PLabelToAddr(ThreadBegin);
+    machineState[InitialPCState] = PLabelToAddr(func);
+    machineState[InitialArgState] = arg;
+    machineState[WhenDonePCState] = PLabelToAddr(ThreadFinish);
 #else
-  machineState[PCState] = (void*)ThreadRoot;
-  machineState[StartupPCState] = (void*)ThreadBegin;
-  machineState[InitialPCState] = (void*)func;
-  machineState[InitialArgState] = (void*)arg;
-  machineState[WhenDonePCState] = (void*)ThreadFinish;
+    machineState[PCState] = (void *)ThreadRoot;
+    machineState[StartupPCState] = (void *)ThreadBegin;
+    machineState[InitialPCState] = (void *)func;
+    machineState[InitialArgState] = (void *)arg;
+    machineState[WhenDonePCState] = (void *)ThreadFinish;
 #endif
 }
 
@@ -367,38 +365,35 @@ Thread::StackAllocate (VoidFunctionPtr func, void *arg)
 // Thread::SaveUserState
 //	Save the CPU state of a user program on a context switch.
 //
-//	Note that a user program thread has *two* sets of CPU registers -- 
-//	one for its state while executing user code, one for its state 
+//	Note that a user program thread has *two* sets of CPU registers --
+//	one for its state while executing user code, one for its state
 //	while executing kernel code.  This routine saves the former.
 //----------------------------------------------------------------------
 
-void
-Thread::SaveUserState()
+void Thread::SaveUserState()
 {
     for (int i = 0; i < NumTotalRegs; i++)
-	userRegisters[i] = kernel->machine->ReadRegister(i);
+        userRegisters[i] = kernel->machine->ReadRegister(i);
 }
 
 //----------------------------------------------------------------------
 // Thread::RestoreUserState
 //	Restore the CPU state of a user program on a context switch.
 //
-//	Note that a user program thread has *two* sets of CPU registers -- 
-//	one for its state while executing user code, one for its state 
+//	Note that a user program thread has *two* sets of CPU registers --
+//	one for its state while executing user code, one for its state
 //	while executing kernel code.  This routine restores the former.
 //----------------------------------------------------------------------
 
-void
-Thread::RestoreUserState()
+void Thread::RestoreUserState()
 {
-  for (int i = 0; i < NumTotalRegs; i++)
-    kernel->machine->WriteRegister(i, userRegisters[i]);
+    for (int i = 0; i < NumTotalRegs; i++)
+        kernel->machine->WriteRegister(i, userRegisters[i]);
 }
 
-
 //----------------------------------------------------------------------
 // SimpleThread
-// 	Loop 5 times, yielding the CPU to another ready thread 
+// 	Loop 5 times, yielding the CPU to another ready thread
 //	each iteration.
 //
 //	"which" is simply a number identifying the thread, for debugging
@@ -409,27 +404,40 @@ static void
 SimpleThread(int which)
 {
     int num;
-    
-    for (num = 0; num < 5; num++) {
-	cout << "*** thread " << which << " looped " << num << " times\n";
+
+    for (num = 0; num < 5; num++)
+    {
+        cout << "*** thread " << which << " looped " << num << " times\n";
         kernel->currentThread->Yield();
     }
 }
 
 //----------------------------------------------------------------------
 // Thread::SelfTest
-// 	Set up a ping-pong between two threads, by forking a thread 
+// 	Set up a ping-pong between two threads, by forking a thread
 //	to call SimpleThread, and then calling SimpleThread ourselves.
 //----------------------------------------------------------------------
 
-void
-Thread::SelfTest()
+void Thread::SelfTest()
 {
     DEBUG(dbgThread, "Entering Thread::SelfTest");
 
     Thread *t = new Thread("forked thread", 1);
 
-    t->Fork((VoidFunctionPtr) SimpleThread, (void *) 1);
+    t->Fork((VoidFunctionPtr)SimpleThread, (void *)1);
     kernel->currentThread->Yield();
     SimpleThread(0);
 }
+
+// Todo ----
+int Thread::getPriority() const
+{
+  return priority;
+}
+
+void Thread::setPriority(int p)
+{
+  ASSERT(p >= 0 && p <= 149);
+  priority = p;
+}
+// ---------
diff --git a/code/threads/thread.h b/code/threads/thread.h
index e311430..38f3a30 100644
--- a/code/threads/thread.h
+++ b/code/threads/thread.h
@@ -80,6 +80,10 @@ class Thread {
     int *stackTop;			 // the current stack pointer
     void *machineState[MachineStateSize];  // all registers except for stackTop
 
+    // Todo ----
+    int priority;
+    // ---------
+
   public:
     Thread(char* debugName, int threadID);		// initialize a Thread 
     ~Thread(); 				// deallocate a Thread
@@ -89,6 +93,11 @@ class Thread {
 
     // basic thread operations
 
+    // Todo ----
+    int getPriority() const;
+    void setPriority(int p);
+    // ---------
+
     void Fork(VoidFunctionPtr func, void *arg); 
     				// Make thread run (*func)(arg)
     void Yield();  		// Relinquish the CPU if any 
@@ -97,32 +106,32 @@ class Thread {
 				// relinquish the processor
     void Begin();		// Startup code for the thread	
     void Finish();  		// The thread is done executing
-    
+
     void CheckOverflow();   	// Check if thread stack has overflowed
     void setStatus(ThreadStatus st) { status = st; }
     ThreadStatus getStatus() { return (status); }
-	char* getName() { return (name); }
-    
-	int getID() { return (ID); }
+    char* getName() { return (name); }
+
+    int getID() { return (ID); }
     void Print() { cout << name; }
     void SelfTest();		// test whether thread impl is working
 
   private:
     // some of the private data for this class is listed above
-    
+
     int *stack; 	 	// Bottom of the stack 
-				// NULL if this is the main thread
-				// (If NULL, don't deallocate stack)
+                    // NULL if this is the main thread
+                    // (If NULL, don't deallocate stack)
     ThreadStatus status;	// ready, running or blocked
     char* name;
-	int   ID;
+    int   ID;
     void StackAllocate(VoidFunctionPtr func, void *arg);
-    				// Allocate a stack for thread.
-				// Used internally by Fork()
+    // Allocate a stack for thread.
+    // Used internally by Fork()
 
-// A thread running a user program actually has *two* sets of CPU registers -- 
-// one for its state while executing user code, one for its state 
-// while executing kernel code.
+    // A thread running a user program actually has *two* sets of CPU registers -- 
+    // one for its state while executing user code, one for its state 
+    // while executing kernel code.
 
     int userRegisters[NumTotalRegs];	// user-level CPU register state
 
diff --git a/code/userprog/addrspace.cc b/code/userprog/addrspace.cc
index 451a23b..f71afee 100644
--- a/code/userprog/addrspace.cc
+++ b/code/userprog/addrspace.cc
@@ -27,101 +27,35 @@
 //	object file header, in case the file was generated on a little
 //	endian machine, and we're now running on a big endian machine.
 //----------------------------------------------------------------------
-
-static void 
-SwapHeader (NoffHeader *noffH)
+static void
+SwapHeader(NoffHeader* noffH)
 {
-  noffH->noffMagic = WordToHost(noffH->noffMagic);
-  noffH->code.size = WordToHost(noffH->code.size);
-  noffH->code.virtualAddr = WordToHost(noffH->code.virtualAddr);
-  noffH->code.inFileAddr = WordToHost(noffH->code.inFileAddr);
+    noffH->noffMagic = WordToHost(noffH->noffMagic);
+    noffH->code.size = WordToHost(noffH->code.size);
+    noffH->code.virtualAddr = WordToHost(noffH->code.virtualAddr);
+    noffH->code.inFileAddr = WordToHost(noffH->code.inFileAddr);
 #ifdef RDATA
-  noffH->readonlyData.size = WordToHost(noffH->readonlyData.size);
-  noffH->readonlyData.virtualAddr = 
-    WordToHost(noffH->readonlyData.virtualAddr);
-  noffH->readonlyData.inFileAddr = 
-    WordToHost(noffH->readonlyData.inFileAddr);
+    noffH->readonlyData.size = WordToHost(noffH->readonlyData.size);
+    noffH->readonlyData.virtualAddr =
+        WordToHost(noffH->readonlyData.virtualAddr);
+    noffH->readonlyData.inFileAddr =
+        WordToHost(noffH->readonlyData.inFileAddr);
 #endif 
-  noffH->initData.size = WordToHost(noffH->initData.size);
-  noffH->initData.virtualAddr = WordToHost(noffH->initData.virtualAddr);
-  noffH->initData.inFileAddr = WordToHost(noffH->initData.inFileAddr);
-  noffH->uninitData.size = WordToHost(noffH->uninitData.size);
-  noffH->uninitData.virtualAddr = WordToHost(noffH->uninitData.virtualAddr);
-  noffH->uninitData.inFileAddr = WordToHost(noffH->uninitData.inFileAddr);
+    noffH->initData.size = WordToHost(noffH->initData.size);
+    noffH->initData.virtualAddr = WordToHost(noffH->initData.virtualAddr);
+    noffH->initData.inFileAddr = WordToHost(noffH->initData.inFileAddr);
+    noffH->uninitData.size = WordToHost(noffH->uninitData.size);
+    noffH->uninitData.virtualAddr = WordToHost(noffH->uninitData.virtualAddr);
+    noffH->uninitData.inFileAddr = WordToHost(noffH->uninitData.inFileAddr);
 
 #ifdef RDATA
-  DEBUG(dbgAddr, "code = " << noffH->code.size <<  
-                 " readonly = " << noffH->readonlyData.size <<
-                 " init = " << noffH->initData.size <<
-                 " uninit = " << noffH->uninitData.size << "\n");
+    DEBUG(dbgAddr, "code = " << noffH->code.size <<
+        " readonly = " << noffH->readonlyData.size <<
+        " init = " << noffH->initData.size <<
+        " uninit = " << noffH->uninitData.size << "\n");
 #endif
 }
 
-FrameTable::Node::Node(int idx):
-  next(nullptr), idx(idx) {}
-
-FrameTable::FrameTable()
-{
-  available = NumPhysPages;
-  useCount = new int[NumPhysPages];
-  begin = end = new FrameTable::Node;
-  for (int i = 0; i < NumPhysPages; i++) {
-    useCount[i] = 0;
-    end->idx = i;
-    end->next = new FrameTable::Node;
-    end = end->next;
-  }
-}
-
-FrameTable::~FrameTable()
-{
-  delete[] useCount;
-  while (begin != end) {
-    FrameTable::Node *tmpNode = begin;
-    begin = begin->next;
-    delete tmpNode;
-  }
-  delete begin;
-}
-
-int FrameTable::Allocate()
-{
-  if (available == 0)
-    return -1;
-
-  int ret = begin->idx;
-  Node *tmp = begin;
-  begin = begin->next;
-  delete tmp;
-
-  --available;
-  useCount[ret]++;
-
-  bzero(kernel->machine->mainMemory + ret * PageSize, PageSize);
-
-  //cerr << "Allocated at page: " << ret << endl;
-  return ret;
-}
-
-void FrameTable::Release(int phyPageNum)
-{
-  useCount[phyPageNum]--;
-
-  if (useCount[phyPageNum] > 0)
-    return;
-
-  ++available;
-
-  //cerr << "Release page: " << end->idx << endl;
-  end->idx = phyPageNum;
-  end->next = new FrameTable::Node;
-}
-
-size_t FrameTable::RemainSize()
-{
-  return available;
-}
-
 //----------------------------------------------------------------------
 // AddrSpace::AddrSpace
 // 	Create an address space to run a user program.
@@ -129,9 +63,24 @@ size_t FrameTable::RemainSize()
 //	memory.  For now, this is really simple (1:1), since we are
 //	only uniprogramming, and we have a single unsegmented page table
 //----------------------------------------------------------------------
-
 AddrSpace::AddrSpace()
-{}
+{
+    pageTable = NULL; // initialize with NULL
+    /*
+        pageTable = new TranslationEntry[NumPhysPages];
+        for (int i = 0; i < NumPhysPages; i++) {
+        pageTable[i].virtualPage = i;	// for now, virt page # = phys page #
+        pageTable[i].physicalPage = i;
+        pageTable[i].valid = TRUE;
+        pageTable[i].use = FALSE;
+        pageTable[i].dirty = FALSE;
+        pageTable[i].readOnly = FALSE;
+        }
+
+        // zero out the entire address space
+        bzero(kernel->machine->mainMemory, MemorySize);
+     */
+}
 
 //----------------------------------------------------------------------
 // AddrSpace::~AddrSpace
@@ -140,10 +89,9 @@ AddrSpace::AddrSpace()
 
 AddrSpace::~AddrSpace()
 {
-  for (int i = 0; i < NumPhysPages; i++)
-    if (pageTable[i].use == TRUE)
-      kernel->frameTable->Release(pageTable[i].physicalPage);
-  delete[] pageTable;
+    /* delete pageTable; */
+    // release frame table by page table
+    kernel->frameTable->Release(pageTable, numPages);
 }
 
 
@@ -156,114 +104,140 @@ AddrSpace::~AddrSpace()
 //
 //	"fileName" is the file containing the object code to load into memory
 //----------------------------------------------------------------------
-
-bool 
-AddrSpace::Load(char *fileName) 
+bool
+AddrSpace::Load(char* fileName)
 {
-  //cerr << "AddrSpace::Load" << endl;
-  OpenFile *executable = kernel->fileSystem->Open(fileName);
-  NoffHeader noffH;
-  unsigned int size;
+    OpenFile* executable = kernel->fileSystem->Open(fileName);
+    NoffHeader noffH;
+    unsigned int size;
 
-  if (executable == NULL) {
-    cerr << "Unable to open file " << fileName << "\n";
-    return FALSE;
-  }
+    if (executable == NULL) {
+        cerr << "Unable to open file " << fileName << "\n";
+        return FALSE;
+    }
 
-  executable->ReadAt((char *)&noffH, sizeof(noffH), 0);
-  if ((noffH.noffMagic != NOFFMAGIC) && 
-    (WordToHost(noffH.noffMagic) == NOFFMAGIC))
-    SwapHeader(&noffH);
-  ASSERT(noffH.noffMagic == NOFFMAGIC);
+    executable->ReadAt((char*)&noffH, sizeof(noffH), 0);
+    if ((noffH.noffMagic != NOFFMAGIC) &&
+        (WordToHost(noffH.noffMagic) == NOFFMAGIC))
+        SwapHeader(&noffH);
+    ASSERT(noffH.noffMagic == NOFFMAGIC);
 
 #ifdef RDATA
-// how big is address space?
-  size = noffH.code.size + noffH.readonlyData.size + noffH.initData.size +
-    noffH.uninitData.size + UserStackSize;	
-  //cerr << noffH.code.size << ' ' 
-  //     << noffH.readonlyData.size << ' '
-  //     << noffH.initData.size << ' '
-  //     << noffH.uninitData.size << ' '
-  //     << UserStackSize << endl;
-  // we need to increase the size
-  // to leave room for the stack
+    // how big is address space?
+    size = noffH.code.size + noffH.readonlyData.size + noffH.initData.size +
+        noffH.uninitData.size + UserStackSize;
+    // we need to increase the size
+// to leave room for the stack
 #else
-// how big is address space?
-  size = noffH.code.size + noffH.initData.size + noffH.uninitData.size 
-    + UserStackSize;	// we need to increase the size
-          // to leave room for the stack
-  //cerr << noffH.code.size << ' ' 
-  //     << noffH.initData.size << ' '
-  //     << noffH.uninitData.size << ' '
-  //     << UserStackSize << endl;
+    // how big is address space?
+    size = noffH.code.size + noffH.initData.size + noffH.uninitData.size
+        + UserStackSize;	// we need to increase the size
+    // to leave room for the stack
 #endif
-  numPages = divRoundUp(size, PageSize);
-  size = numPages * PageSize;
+    numPages = divRoundUp(size, PageSize);
+    size = numPages * PageSize;
 
-  ASSERT(numPages <= NumPhysPages);		// check we're not trying
-          // to run anything too big --
-          // at least until we have
-          // virtual memory
-  
-  pageTable = new TranslationEntry[numPages];
-  for (int i = 0; i < numPages; i++) {
-    pageTable[i].virtualPage = i;
-    pageTable[i].physicalPage = -1;
-    pageTable[i].valid = TRUE;
-    pageTable[i].use = FALSE;
-    pageTable[i].dirty = FALSE;
-    pageTable[i].readOnly = FALSE;
-  }
-
-  DEBUG(dbgAddr, "Initializing address space: " << numPages << ", " << size);
-
-// then, copy in the code and data segments into memory
-  if (noffH.code.size > 0) {
-    DEBUG(dbgAddr, "Initializing code segment.");
-    DEBUG(dbgAddr, noffH.code.virtualAddr << ", " << noffH.code.size);
-
-    for (size_t cur = 0; cur < (size_t)noffH.code.size; cur += PageSize) {
-      size_t physAddr, size = min((size_t)PageSize, noffH.code.size - cur);
-      Translate(noffH.code.virtualAddr + cur, &physAddr, 1);
-      //cerr << "physAddr, size: " << physAddr << ' ' << size << endl;
-
-      executable->ReadAt(
-        &(kernel->machine->mainMemory[physAddr]), size,
-        noffH.code.inFileAddr + cur);
+    pageTable = kernel->frameTable->Allocate(numPages);
+    if (!pageTable) {
+        kernel->interrupt->setStatus(SystemMode);
+        ExceptionHandler(MemoryLimitException);
+        kernel->interrupt->setStatus(UserMode);
     }
-  }
-  if (noffH.initData.size > 0) {
-    DEBUG(dbgAddr, "Initializing data segment.");
-    DEBUG(dbgAddr, noffH.initData.virtualAddr << ", " << noffH.initData.size);
 
-    for (size_t cur = 0; cur < (size_t)noffH.initData.size; cur += PageSize) {
-      size_t physAddr, size = min((size_t)PageSize, noffH.initData.size - cur);
-      Translate(noffH.initData.virtualAddr + cur, &physAddr, 1);
+    DEBUG(dbgAddr, "Initializing address space: " << numPages << ", " << size);
 
-      executable->ReadAt(
-        &(kernel->machine->mainMemory[physAddr]), size,
-        noffH.initData.inFileAddr + cur);
+    // then, copy in the code and data segments into memory
+    uint paddr; // physical address
+    ExceptionType ex; // occurring exception
+    int sz, // total size to load
+        vaddr, // base virtual address
+        fpos, // base file position
+        to_load; // size to load on each time
+
+    if (noffH.code.size > 0) {
+        DEBUG(dbgAddr, "Initializing code segment.");
+        DEBUG(dbgAddr, noffH.code.virtualAddr << ", " << noffH.code.size);
+
+        sz = noffH.code.size;
+        vaddr = noffH.code.virtualAddr;
+        fpos = noffH.code.inFileAddr;
+
+        for (uint offset = 0; offset < sz; offset += PageSize) {
+            ex = Translate(vaddr + offset, &paddr, 1);
+
+            if (ex != NoException) {
+                kernel->interrupt->setStatus(SystemMode);
+                ExceptionHandler(ex);
+                kernel->interrupt->setStatus(UserMode);
+            }
+
+            to_load = offset + PageSize < sz ? PageSize : sz - offset;
+
+            executable->ReadAt(
+                &(kernel->machine->mainMemory[paddr]),
+                to_load, fpos + offset);
+        }
+    }
+
+    if (noffH.initData.size > 0) {
+        DEBUG(dbgAddr, "Initializing data segment.");
+        DEBUG(dbgAddr, noffH.initData.virtualAddr << ", " << noffH.initData.size);
+
+        sz = noffH.initData.size;
+        vaddr = noffH.initData.virtualAddr;
+        fpos = noffH.initData.inFileAddr;
+
+        for (uint offset = 0; offset < sz; offset += PageSize) {
+            ex = Translate(vaddr + offset, &paddr, 1);
+
+            if (ex != NoException) {
+                kernel->interrupt->setStatus(SystemMode);
+                ExceptionHandler(ex);
+                kernel->interrupt->setStatus(UserMode);
+            }
+
+            to_load = offset + PageSize < sz ? PageSize : sz - offset;
+
+            executable->ReadAt(
+                &(kernel->machine->mainMemory[paddr]),
+                to_load, fpos + offset);
+        }
     }
-  }
 
 #ifdef RDATA
-  if (noffH.readonlyData.size > 0) {
-    DEBUG(dbgAddr, "Initializing read only data segment.");
-    DEBUG(dbgAddr, noffH.readonlyData.virtualAddr << ", " << noffH.readonlyData.size);
+    if (noffH.readonlyData.size > 0) {
+        DEBUG(dbgAddr, "Initializing read only data segment.");
+        DEBUG(dbgAddr, noffH.readonlyData.virtualAddr << ", " << noffH.readonlyData.size);
 
-    for (size_t cur = 0; cur < (size_t)noffH.readonlyData.size; cur += PageSize) {
-      size_t physAddr, size = min((size_t)PageSize, noffH.readonlyData.size - cur);
-      Translate(noffH.readonlyData.virtualAddr + cur, &physAddr, 1);
+        sz = noffH.readonlyData.size;
+        vaddr = noffH.readonlyData.virtualAddr;
+        fpos = noffH.readonlyData.inFileAddr;
 
-      executable->ReadAt(
-        &(kernel->machine->mainMemory[physAddr]),
-        size, noffH.readonlyData.inFileAddr + cur);
+        // read only flag for page table
+        for (int i = 0, lim = divRoundUp(sz, PageSize),
+            from = vaddr / PageSize; i < lim; ++i)
+            pageTable[from + i].readOnly = TRUE;
+
+        for (uint offset = 0; offset < sz; offset += PageSize) {
+            ex = Translate(vaddr + offset, &paddr, 0); // read only
+
+            if (ex != NoException) {
+                kernel->interrupt->setStatus(SystemMode);
+                ExceptionHandler(ex);
+                kernel->interrupt->setStatus(UserMode);
+            }
+
+            to_load = offset + PageSize < sz ? PageSize : sz - offset;
+
+            executable->ReadAt(
+                &(kernel->machine->mainMemory[paddr]),
+                to_load, fpos + offset);
+        }
     }
-  }
 #endif
 
-  delete executable;			// close file
-  return TRUE;			// success
+    delete executable;			// close file
+    return TRUE;			// success
 }
 
 //----------------------------------------------------------------------
@@ -274,21 +248,20 @@ AddrSpace::Load(char *fileName)
 //      the address space
 //
 //----------------------------------------------------------------------
-
-void 
-AddrSpace::Execute(char* fileName) 
+void
+AddrSpace::Execute(char* fileName)
 {
-  //cerr << "AddrSpace::Execute" << endl;
-  kernel->currentThread->space = this;
 
-  this->InitRegisters();		// set the initial register values
-  this->RestoreState();		// load page table register
+    kernel->currentThread->space = this;
 
-  kernel->machine->Run();		// jump to the user progam
+    this->InitRegisters();		// set the initial register values
+    this->RestoreState();		// load page table register
 
-  ASSERTNOTREACHED();			// machine->Run never returns;
-        // the address space exits
-        // by doing the syscall "exit"
+    kernel->machine->Run();		// jump to the user program
+
+    ASSERTNOTREACHED();			// machine->Run never returns;
+    // the address space exits
+    // by doing the syscall "exit"
 }
 
 
@@ -301,31 +274,30 @@ AddrSpace::Execute(char* fileName)
 //	will be saved/restored into the currentThread->userRegisters
 //	when this thread is context switched out.
 //----------------------------------------------------------------------
-
 void
 AddrSpace::InitRegisters()
 {
-  Machine *machine = kernel->machine;
-  int i;
+    Machine* machine = kernel->machine;
+    int i;
 
-  for (i = 0; i < NumTotalRegs; i++)
-    machine->WriteRegister(i, 0);
+    for (i = 0; i < NumTotalRegs; i++)
+        machine->WriteRegister(i, 0);
 
-  // Initial program counter -- must be location of "Start", which
-  //  is assumed to be virtual address zero
-  machine->WriteRegister(PCReg, 0);	
+    // Initial program counter -- must be location of "Start", which
+    //  is assumed to be virtual address zero
+    machine->WriteRegister(PCReg, 0);
 
-  // Need to also tell MIPS where next instruction is, because
-  // of branch delay possibility
-  // Since instructions occupy four bytes each, the next instruction
-  // after start will be at virtual address four.
-  machine->WriteRegister(NextPCReg, 4);
+    // Need to also tell MIPS where next instruction is, because
+    // of branch delay possibility
+    // Since instructions occupy four bytes each, the next instruction
+    // after start will be at virtual address four.
+    machine->WriteRegister(NextPCReg, 4);
 
- // Set the stack register to the end of the address space, where we
- // allocated the stack; but subtract off a bit, to make sure we don't
- // accidentally reference off the end!
-  machine->WriteRegister(StackReg, numPages * PageSize - 16);
-  DEBUG(dbgAddr, "Initializing stack pointer: " << numPages * PageSize - 16);
+    // Set the stack register to the end of the address space, where we
+    // allocated the stack; but subtract off a bit, to make sure we don't
+    // accidentally reference off the end!
+    machine->WriteRegister(StackReg, numPages * PageSize - 16);
+    DEBUG(dbgAddr, "Initializing stack pointer: " << numPages * PageSize - 16);
 }
 
 //----------------------------------------------------------------------
@@ -335,9 +307,9 @@ AddrSpace::InitRegisters()
 //
 //	For now, don't need to save anything!
 //----------------------------------------------------------------------
-
-void AddrSpace::SaveState() 
-{}
+void AddrSpace::SaveState()
+{
+}
 
 //----------------------------------------------------------------------
 // AddrSpace::RestoreState
@@ -346,11 +318,10 @@ void AddrSpace::SaveState()
 //
 //      For now, tell the machine where to find the page table.
 //----------------------------------------------------------------------
-
-void AddrSpace::RestoreState() 
+void AddrSpace::RestoreState()
 {
-  kernel->machine->pageTable = pageTable;
-  kernel->machine->pageTableSize = numPages;
+    kernel->machine->pageTable = pageTable;
+    kernel->machine->pageTableSize = numPages;
 }
 
 
@@ -363,50 +334,84 @@ void AddrSpace::RestoreState()
 //  Return any exceptions caused by the address translation.
 //----------------------------------------------------------------------
 ExceptionType
-AddrSpace::Translate(unsigned int vaddr, unsigned int *paddr, int isReadWrite)
+AddrSpace::Translate(unsigned int vaddr, unsigned int* paddr, int isReadWrite)
 {
-  TranslationEntry *pte;
-  int               pfn;
-  unsigned int      vpn    = vaddr / PageSize;
-  unsigned int      offset = vaddr % PageSize;
+    TranslationEntry* pte;
+    int               pfn;
+    unsigned int      vpn = vaddr / PageSize;
+    unsigned int      offset = vaddr % PageSize;
 
-  if(vpn >= numPages) {
-    return AddressErrorException;
-  }
-
-  pte = &pageTable[vpn];
-
-  if(isReadWrite && pte->readOnly) {
-    return ReadOnlyException;
-  }
-
-  pfn = pte->physicalPage;
-  if (pfn == -1) {
-    pfn = pte->physicalPage = kernel->frameTable->Allocate();
-    if (pfn == -1) {
-      DEBUG(dbgAddr, "Memory Limit exceeded");
-      return MemoryLimitException;
+    if (vpn >= numPages) {
+        return AddressErrorException;
     }
-  }
 
-  // if the pageFrame is too big, there is something really wrong!
-  // An invalid translation was loaded into the page table or TLB.
-  if (pfn >= NumPhysPages) {
-    DEBUG(dbgAddr, "Illegal physical page " << pfn);
-    return BusErrorException;
-  }
+    pte = &pageTable[vpn];
 
-  pte->use = TRUE;          // set the use, dirty bits
+    if (isReadWrite && pte->readOnly) {
+        return ReadOnlyException;
+    }
 
-  if(isReadWrite)
-    pte->dirty = TRUE;
+    pfn = pte->physicalPage;
 
-  *paddr = pfn * PageSize + offset;
+    // if the pageFrame is too big, there is something really wrong!
+    // An invalid translation was loaded into the page table or TLB.
+    if (pfn >= NumPhysPages) {
+        DEBUG(dbgAddr, "Illegal physical page " << pfn);
+        return BusErrorException;
+    }
 
-  ASSERT((*paddr < MemorySize));
+    pte->use = TRUE;          // set the use, dirty bits
 
-  //cerr << " -- AddrSpace::Translate(): vaddr: " << vaddr <<
-  //  ", paddr: " << *paddr << "\n";
+    if (isReadWrite)
+        pte->dirty = TRUE;
 
-  return NoException;
+    *paddr = pfn * PageSize + offset;
+
+    ASSERT((*paddr < MemorySize));
+
+    //cerr << " -- AddrSpace::Translate(): vaddr: " << vaddr <<
+    //  ", paddr: " << *paddr << "\n";
+
+    return NoException;
 }
+
+FrameTable::FrameTable() {
+    for (int i = 0; i < NumPhysPages; ++i)
+        available.Append(i);
+}
+
+FrameTable::~FrameTable() {}
+
+uint FrameTable::RemainSize() { return available.NumInList(); }
+
+PageTable FrameTable::Allocate(uint pageNum) {
+    // if not enough memory
+    if (RemainSize() < pageNum)
+        return NULL;
+
+    PageTable ptb = new TranslationEntry[pageNum];
+
+    for (int i = 0; i < pageNum; ++i) {
+        ptb[i].virtualPage = i;
+        int f = available.RemoveFront(); // frame number
+        ptb[i].physicalPage = f;
+        // initialize flags
+        ptb[i].valid = TRUE;
+        ptb[i].use = FALSE;
+        ptb[i].dirty = FALSE;
+        ptb[i].readOnly = FALSE;
+        // zero out the entire address space
+        bzero(kernel->machine->mainMemory + f * PageSize, PageSize);
+    }
+    return ptb;
+}
+
+void FrameTable::Release(PageTable ptb, int pageNum) {
+    if (!ptb)
+        return; // nothing to release
+    for (int i = 0; i < pageNum; ++i)
+        available.Append(ptb[i].physicalPage);
+    delete[] ptb;
+}
+
+
diff --git a/code/userprog/addrspace.h b/code/userprog/addrspace.h
index fa9c104..0da4575 100644
--- a/code/userprog/addrspace.h
+++ b/code/userprog/addrspace.h
@@ -18,57 +18,84 @@
 
 #define UserStackSize		1024 	// increase this as necessary!
 
-class FrameTable {
-  public:
-    FrameTable();
-    ~FrameTable();
-
-    int Allocate();
-    void Release(int phyPageNum);
-    size_t RemainSize();
-
-  private:
-    struct Node {
-      Node *next;
-      int idx;
-      Node(int idx = -1);
-    };
-
-    Node *begin, *end;
-
-    size_t available;
-    int *useCount;
-};
-
 class AddrSpace {
-  public:
-    AddrSpace();			// Create an address space.
-    ~AddrSpace();			// De-allocate an address space
+public:
+  AddrSpace();			// Create an address space.
+  ~AddrSpace();			// De-allocate an address space
 
-    bool Load(char *fileName);		// Load a program into addr space from
-                                        // a file
-					// return false if not found
+  bool Load(char* fileName);		// Load a program into addr space from
+  // a file
+// return false if not found
 
-    void Execute(char *fileName);             	// Run a program
-					// assumes the program has already
-                                        // been loaded
+  void Execute(char* fileName);             	// Run a program
+  // assumes the program has already
+                                // been loaded
 
-    void SaveState();			// Save/restore address space-specific
-    void RestoreState();		// info on a context switch 
+  void SaveState();			// Save/restore address space-specific
+  void RestoreState();		// info on a context switch 
 
-    // Translate virtual address _vaddr_
-    // to physical address _paddr_. _mode_
-    // is 0 for Read, 1 for Write.
-    ExceptionType Translate(unsigned int vaddr, unsigned int *paddr, int mode);
+  // Translate virtual address _vaddr_
+  // to physical address _paddr_. _mode_
+  // is 0 for Read, 1 for Write.
+  ExceptionType Translate(unsigned int vaddr, unsigned int* paddr, int mode);
 
-  private:
-    TranslationEntry *pageTable;
-    unsigned int numPages;		// Number of pages in the virtual 
-					// address space
+private:
+  TranslationEntry* pageTable;	// Assume linear page table translation
+  // for now!
+  unsigned int numPages;		// Number of pages in the virtual 
+  // address space
 
-    void InitRegisters();		// Initialize user-level CPU registers,
-					// before jumping to user code
+  void InitRegisters();		// Initialize user-level CPU registers,
+  // before jumping to user code
 
 };
 
 #endif // ADDRSPACE_H
+
+#ifndef FRAME_TABLE_H
+#define FRAME_TABLE_H
+
+#include "machine.h"
+#include "list.h"
+
+/**
+ * Data structure of Virtual Memory
+ */
+typedef TranslationEntry* PageTable;
+
+/**
+ * Data structure of Physical Memory
+ */
+class FrameTable {
+public:
+  /**
+   * Initialize a frame table
+   */
+  FrameTable();
+  ~FrameTable();
+
+  /**
+   * Allocate pageNum of frames (pages) and collect
+   * corresponding translation information into a page table.
+   *
+   * @param pageNum numbers of pages
+   * @return a new Page table, NULL if not enough memory space
+   */
+  PageTable Allocate(uint pageNum);
+
+  /**
+   * Release the physical memory frame
+   * which the info stored in PageTable
+   */
+  void Release(PageTable ptb, int pageNum);
+
+  /**
+   * @return the remaining numbers of entry of the frame table
+   */
+  uint RemainSize();
+
+private:
+  List<int> available;
+};
+
+#endif /* FRAME_TABLE_H */
\ No newline at end of file
diff --git a/code/userprog/exception.cc b/code/userprog/exception.cc
index c7be4ba..a9363d1 100644
--- a/code/userprog/exception.cc
+++ b/code/userprog/exception.cc
@@ -1,18 +1,18 @@
 // exception.cc 
-//  Entry point into the Nachos kernel from user programs.
-//  There are two kinds of things that can cause control to
-//  transfer back to here from user code:
+//	Entry point into the Nachos kernel from user programs.
+//	There are two kinds of things that can cause control to
+//	transfer back to here from user code:
 //
-//  syscall -- The user code explicitly requests to call a procedure
-//  in the Nachos kernel.  Right now, the only function we support is
-//  "Halt".
+//	syscall -- The user code explicitly requests to call a procedure
+//	in the Nachos kernel.  Right now, the only function we support is
+//	"Halt".
 //
-//  exceptions -- The user code does something that the CPU can't handle.
-//  For instance, accessing memory that doesn't exist, arithmetic errors,
-//  etc.  
+//	exceptions -- The user code does something that the CPU can't handle.
+//	For instance, accessing memory that doesn't exist, arithmetic errors,
+//	etc.  
 //
-//  Interrupts (which can also cause control to transfer from user
-//  code into the Nachos kernel) are handled elsewhere.
+//	Interrupts (which can also cause control to transfer from user
+//	code into the Nachos kernel) are handled elsewhere.
 //
 // For now, this only handles the Halt() system call.
 // Everything else core dumps.
@@ -27,192 +27,170 @@
 #include "ksyscall.h"
 //----------------------------------------------------------------------
 // ExceptionHandler
-//   Entry point into the Nachos kernel.  Called when a user program
-//  is executing, and either does a syscall, or generates an addressing
-//  or arithmetic exception.
+// 	Entry point into the Nachos kernel.  Called when a user program
+//	is executing, and either does a syscall, or generates an addressing
+//	or arithmetic exception.
 //
-//   For system calls, the following is the calling convention:
+// 	For system calls, the following is the calling convention:
 //
-//   system call code -- r2
-//  	arg1 -- r4
-//  	arg2 -- r5
-//  	arg3 -- r6
-//  	arg4 -- r7
+// 	system call code -- r2
+//		arg1 -- r4
+//		arg2 -- r5
+//		arg3 -- r6
+//		arg4 -- r7
 //
-//  The result of the system call, if any, must be put back into r2. 
+//	The result of the system call, if any, must be put back into r2. 
 //
 // If you are handling a system call, don't forget to increment the pc
 // before returning. (Or else you'll loop making the same system call forever!)
 //
-//  "which" is the kind of exception.  The list of possible exceptions 
-//  is in machine.h.
+//	"which" is the kind of exception.  The list of possible exceptions 
+//	is in machine.h.
 //----------------------------------------------------------------------
 
 void
 ExceptionHandler(ExceptionType which)
 {
-  int type = kernel->machine->ReadRegister(2);
-  int val;
-  int status, exit, threadID, programID;
-  DEBUG(dbgSys, "Received Exception " << which << " type: " << type << "\n");
-  switch (which) {
-    case SyscallException:
-      switch(type) {
-        case SC_Halt:
-  		    DEBUG(dbgSys, "Shutdown, initiated by user program.\n");
-  		    SysHalt();
-          cout<<"in exception\n";
-          ASSERTNOTREACHED();
-          break;
-  	    case SC_MSG:
-          DEBUG(dbgSys, "Message received.\n");
-          val = kernel->machine->ReadRegister(4);
-          {
-            char *msg = &(kernel->machine->mainMemory[val]);
-            cout << msg << endl;
-          }
-          SysHalt();
-          ASSERTNOTREACHED();
-          break;
-        case SC_Create:
-          val = kernel->machine->ReadRegister(4);
-          {
-            char *filename = &(kernel->machine->mainMemory[val]);
-            //cout << filename << endl;
-            status = SysCreate(filename);
-            kernel->machine->WriteRegister(2, (int) status);
-          }
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          return;
-          ASSERTNOTREACHED();
-          break;
-        case SC_Add:
-          DEBUG(dbgSys, "Add " << kernel->machine->ReadRegister(4) << " + " << kernel->machine->ReadRegister(5) << "\n");
-          /* Process SysAdd Systemcall*/
-          int result;
-          result = SysAdd(/* int op1 */(int)kernel->machine->ReadRegister(4),
-          /* int op2 */(int)kernel->machine->ReadRegister(5));
-          DEBUG(dbgSys, "Add returning with " << result << "\n");
-          /* Prepare Result */
-          kernel->machine->WriteRegister(2, (int)result);	
-          /* Modify return point */
-          {
-            /* set previous programm counter (debugging only)*/
-            kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-              
-            /* set programm counter to next instruction (all Instructions are 4 byte wide)*/
-            kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-        
-            /* set next programm counter for brach execution */
-            kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          }
-          cout << "result is " << result << "\n";	
-          return;	
-          ASSERTNOTREACHED();
-          break;
-        case SC_Exit:
-          DEBUG(dbgAddr, "Program exit\n");
-          val = kernel->machine->ReadRegister(4);
-          cout << "return value:" << val << endl;
-          kernel->currentThread->Finish();
-          break;
-        case SC_PrintInt:
-          DEBUG(dbgAddr, "Printing int\n");
-          val = (int)kernel->machine->ReadRegister(4);
-          SysPrintInt(val);
+	int type = kernel->machine->ReadRegister(2);
+	int val;
+	int status, exit, threadID, programID;
+	int fd, size;
+	DEBUG(dbgSys, "Received Exception " << which << " type: " << type << "\n");
+	switch (which) {
+	case SyscallException:
+		switch (type) {
+		case SC_Halt:
+			DEBUG(dbgSys, "Shutdown, initiated by user program.\n");
+			SysHalt();
+			cout << "in exception\n";
+			ASSERTNOTREACHED();
+			break;
+		case SC_MSG:
+			DEBUG(dbgSys, "Message received.\n");
+			val = kernel->machine->ReadRegister(4);
+			{
+				char* msg = &(kernel->machine->mainMemory[val]);
+				cout << msg << endl;
+			}
+			SysHalt();
+			ASSERTNOTREACHED();
+			break;
+		case SC_PrintInt:
+			val = kernel->machine->ReadRegister(4);
+			SysPrintInt(val);
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+		case SC_Create:
+			val = kernel->machine->ReadRegister(4);
+			{
+				char* filename = &(kernel->machine->mainMemory[val]);
+				//cout << filename << endl;
+				status = SysCreate(filename);
+				kernel->machine->WriteRegister(2, (int)status);
+			}
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Open:
+			val = kernel->machine->ReadRegister(4);
+			{
+				char* filename = &(kernel->machine->mainMemory[val]);
+				//cout << filename << endl;
+				fd = SysOpen(filename);
+				kernel->machine->WriteRegister(2, (int)fd);
+			}
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Write:
+			val = kernel->machine->ReadRegister(4);
+			size = kernel->machine->ReadRegister(5);
+			fd = kernel->machine->ReadRegister(6);
+			{
+				char* buffer = &(kernel->machine->mainMemory[val]);
+				size = SysWrite(buffer, size, fd);
+				kernel->machine->WriteRegister(2, (int)size);
+			}
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Close:
+			fd = kernel->machine->ReadRegister(4);
+			{
+				val = SysClose(fd);
+				kernel->machine->WriteRegister(2, (int)val);
+			}
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Read:
+			val = kernel->machine->ReadRegister(4);
+			size = kernel->machine->ReadRegister(5);
+			fd = kernel->machine->ReadRegister(6);
+			{
+				char* buffer = &(kernel->machine->mainMemory[val]);
+				size = SysRead(buffer, size, fd);
+				kernel->machine->WriteRegister(2, (int)size);
+			}
+			kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
+			kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Add:
+			DEBUG(dbgSys, "Add " << kernel->machine->ReadRegister(4) << " + " << kernel->machine->ReadRegister(5) << "\n");
+			/* Process SysAdd Systemcall*/
+			int result;
+			result = SysAdd(/* int op1 */(int)kernel->machine->ReadRegister(4),
+				/* int op2 */(int)kernel->machine->ReadRegister(5));
+			DEBUG(dbgSys, "Add returning with " << result << "\n");
+			/* Prepare Result */
+			kernel->machine->WriteRegister(2, (int)result);
+			/* Modify return point */
+			{
+				/* set previous programm counter (debugging only)*/
+				kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
 
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          
-          return;
-          ASSERTNOTREACHED();
-          break;
-        case SC_Open:
-          DEBUG(dbgAddr, "Open file\n");
+				/* set programm counter to next instruction (all Instructions are 4 byte wide)*/
+				kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
 
-          {
-            val = kernel->machine->ReadRegister(4);
-            char *name = &(kernel->machine->mainMemory[val]);
-            OpenFileId ret = SysOpen(name);
-            kernel->machine->WriteRegister(2, ret);
-          }
- 
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-
-          return;
-          ASSERTNOTREACHED();
-          break;
-        case SC_Read:
-          DEBUG(dbgAddr, "Read file\n");
-
-          {
-            val = kernel->machine->ReadRegister(4);
-            char *buffer = &(kernel->machine->mainMemory[val]);
-            int size = kernel->machine->ReadRegister(5);
-            OpenFileId id = (OpenFileId)kernel->machine->ReadRegister(6);
-            int ret = SysRead(buffer, size, id);
-            kernel->machine->WriteRegister(2, ret);
-          }
-
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-
-          return;
-          ASSERTNOTREACHED();
-          break;
-        case SC_Write:
-          DEBUG(dbgAddr, "Write file\n");
-
-          {
-            val = kernel->machine->ReadRegister(4);
-            char *buffer = &(kernel->machine->mainMemory[val]);
-            int size = kernel->machine->ReadRegister(5);
-            OpenFileId id = (OpenFileId)kernel->machine->ReadRegister(6);
-            // fprintf(stderr, "buffer: %p\n", buffer);
-            // cerr << "size: " << size << endl;
-            // cerr << "id: " << id << endl;
-            int ret = SysWrite(buffer, size, id);
-            kernel->machine->WriteRegister(2, ret);
-          }
-
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-
-          return;
-          ASSERTNOTREACHED();
-          break;
-        case SC_Close:
-          DEBUG(dbgAddr, "Close file\n");
-
-          {
-            OpenFileId id = (OpenFileId)kernel->machine->ReadRegister(4);
-            int ret = SysClose(id);
-            kernel->machine->WriteRegister(2, ret);
-          }
-
-          kernel->machine->WriteRegister(PrevPCReg, kernel->machine->ReadRegister(PCReg));
-          kernel->machine->WriteRegister(PCReg, kernel->machine->ReadRegister(PCReg) + 4);
-          kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
-
-          return;
-          ASSERTNOTREACHED();
-          break;
-        default:
-          cerr << "Unexpected system call " << type << "\n";
-          break;
-  	  }
-  	  break;
-    default:
-      cerr << "Unexpected user mode exception " << (int)which << "\n";
-      break;
-  }
-  ASSERTNOTREACHED();
+				/* set next programm counter for brach execution */
+				kernel->machine->WriteRegister(NextPCReg, kernel->machine->ReadRegister(PCReg) + 4);
+			}
+			cout << "result is " << result << "\n";
+			return;
+			ASSERTNOTREACHED();
+			break;
+		case SC_Exit:
+			DEBUG(dbgAddr, "Program exit\n");
+			val = kernel->machine->ReadRegister(4);
+			cout << "return value:" << val << endl;
+			kernel->currentThread->Finish();
+			break;
+		default:
+			cerr << "Unexpected system call " << type << "\n";
+			break;
+		}
+		break;
+	default:
+		cerr << "Unexpected user mode exception " << (int)which << "\n";
+		break;
+	}
+	ASSERTNOTREACHED();
 }
 
diff --git a/code/userprog/hw4_consoleIO_1.c b/code/userprog/hw4_consoleIO_1.c
new file mode 100644
index 0000000..ef6c61b
--- /dev/null
+++ b/code/userprog/hw4_consoleIO_1.c
@@ -0,0 +1,11 @@
+#include "syscall.h"
+
+int
+main()
+{
+  int n;
+  for (n = 0; n < 4; n++) {
+    PrintInt(1);
+  }
+  return 0;
+}
diff --git a/code/userprog/hw4_consoleIO_2.c b/code/userprog/hw4_consoleIO_2.c
new file mode 100644
index 0000000..685d7d4
--- /dev/null
+++ b/code/userprog/hw4_consoleIO_2.c
@@ -0,0 +1,11 @@
+#include "syscall.h"
+
+int
+main()
+{
+  int n;
+  for (n = 0; n < 5; n++) {
+    PrintInt(2);
+  }
+  return 0;
+}
diff --git a/code/userprog/hw4_consoleIO_3.c b/code/userprog/hw4_consoleIO_3.c
new file mode 100644
index 0000000..9092129
--- /dev/null
+++ b/code/userprog/hw4_consoleIO_3.c
@@ -0,0 +1,12 @@
+#include "syscall.h"
+
+int
+main()
+{
+  int n;
+
+  for (n = 0; n < 12; n++) {
+    PrintInt(3);
+  }
+  return 0;
+}
diff --git a/code/userprog/hw4_consoleIO_4.c b/code/userprog/hw4_consoleIO_4.c
new file mode 100644
index 0000000..70877e7
--- /dev/null
+++ b/code/userprog/hw4_consoleIO_4.c
@@ -0,0 +1,12 @@
+#include "syscall.h"
+
+int
+main()
+{
+  int n;
+
+  for (n = 0; n < 11; n++) {
+    PrintInt(4);
+  }
+  return 0;
+}
diff --git a/code/userprog/ksyscall.h b/code/userprog/ksyscall.h
index 6b315f7..309f873 100644
--- a/code/userprog/ksyscall.h
+++ b/code/userprog/ksyscall.h
@@ -1,78 +1,71 @@
-/**************************************************************
- *
- * userprog/ksyscall.h
- *
- * Kernel interface for systemcalls 
- *
- * by Marcus Voelp  (c) Universitaet Karlsruhe
- *
- **************************************************************/
-
-#ifndef __USERPROG_KSYSCALL_H__ 
-#define __USERPROG_KSYSCALL_H__ 
-
-#define INT_BUF_LENGTH 13
-
-#include "kernel.h"
-
-#include "synchconsole.h"
-
-
-void SysHalt()
-{
-  kernel->interrupt->Halt();
-}
-
-int SysAdd(int op1, int op2)
-{
-  return op1 + op2;
-}
-
-int SysCreate(char *filename)
-{
-  // return value
-  // 1: success
-  // 0: failed
-  return kernel->interrupt->CreateFile(filename);
-}
-
-void SysPrintInt(int value) {
-  kernel->interrupt->PrintInt(value);
-}
-
-OpenFileId SysOpen(char *name) {
-  OpenFileId id = -1;
-  for (int i = 0; i < 20; i++)
-    if (kernel->fileSystem->fileDescriptorTable[i] == NULL) {
-      id = i;
-      kernel->fileSystem->fileDescriptorTable[i] 
-        = kernel->fileSystem->Open(name);
-      if (kernel->fileSystem->fileDescriptorTable[i] == NULL)
-        return -1;
-      break;
-    }
-  return id;
-}
-
-int SysWrite(char *buffer, int size, OpenFileId id) {
-  if (id < 0 || id >= 20 || kernel->fileSystem->fileDescriptorTable[id] == NULL)
-    return -1;
-  return kernel->fileSystem->fileDescriptorTable[id]->Write(buffer, size);
-}
-
-int SysRead(char *buffer, int size, OpenFileId id) {
-  if (id < 0 || id >= 20 || kernel->fileSystem->fileDescriptorTable[id] == NULL)
-    return -1;
-  return kernel->fileSystem->fileDescriptorTable[id]->Read(buffer, size);
-}
-
-int SysClose(OpenFileId id) {
-  if (id < 0 || id >= 20 || kernel->fileSystem->fileDescriptorTable[id] == NULL)
-    return 0;
-  delete kernel->fileSystem->fileDescriptorTable[id];
-  kernel->fileSystem->fileDescriptorTable[id] = NULL;
-  return 1;
-}
-
-
-#endif /* ! __USERPROG_KSYSCALL_H__ */
+/**************************************************************
+ *
+ * userprog/ksyscall.h
+ *
+ * Kernel interface for systemcalls
+ *
+ * by Marcus Voelp  (c) Universitaet Karlsruhe
+ *
+ **************************************************************/
+
+#ifndef __USERPROG_KSYSCALL_H__ 
+#define __USERPROG_KSYSCALL_H__ 
+
+#include "kernel.h"
+
+#include "synchconsole.h"
+
+typedef int OpenFileId;
+
+void SysHalt()
+{
+	kernel->interrupt->Halt();
+}
+
+int SysAdd(int op1, int op2)
+{
+	return op1 + op2;
+}
+
+int SysCreate(char* filename)
+{
+	// return value
+	// 1: success
+	// 0: failed
+	return kernel->interrupt->CreateFile(filename);
+}
+
+void SysPrintInt(int value)
+{
+	kernel->interrupt->PrintInt(value);
+}
+
+// -1: open fail
+// fd
+OpenFileId SysOpen(char* filename)
+{
+	return kernel->interrupt->OpenFile(filename);
+}
+
+// -1: write fail
+// size 
+int SysWrite(char* buffer, int size, OpenFileId fd)
+{
+	return kernel->interrupt->WriteFile(buffer, size, fd);
+}
+
+// 1: close success
+// 0: close fail
+int SysClose(OpenFileId fd)
+{
+	return kernel->interrupt->CloseFile(fd);
+}
+
+// -1: read fail
+// size
+int SysRead(char* buffer, int size, OpenFileId fd)
+{
+	return kernel->interrupt->ReadFile(buffer, size, fd);
+}
+
+#endif /* ! __USERPROG_KSYSCALL_H__ */
diff --git a/code/userprog/noff.h b/code/userprog/noff.h
index a8b5551..7fda56f 100644
--- a/code/userprog/noff.h
+++ b/code/userprog/noff.h
@@ -1,4 +1,4 @@
-/* noff.h 
+/* noff.h
  *     Data structures defining the Nachos Object Code Format
  *
  *     Basically, we only know about three types of segments:
@@ -6,23 +6,22 @@
  */
 
 #define NOFFMAGIC	0xbadfad 	/* magic number denoting Nachos 
-					 * object code file 
-					 */
+                              /* object code file*/
 
 typedef struct segment {
-  int virtualAddr;		/* location of segment in virt addr space */
-  int inFileAddr;		/* location of segment in this file */
-  int size;			/* size of segment */
+   int virtualAddr;		/* location of segment in virt addr space */
+   int inFileAddr;		/* location of segment in this file */
+   int size;			/* size of segment */
 } Segment;
 
 typedef struct noffHeader {
    int noffMagic;		/* should be NOFFMAGIC */
-   Segment code;		/* executable code segment */ 
+   Segment code;		/* executable code segment */
    Segment initData;		/* initialized data segment */
 #ifdef RDATA
    Segment readonlyData;	/* read only data */
 #endif
    Segment uninitData;		/* uninitialized data segment --
-				 * should be zero'ed before use 
-				 */
+             * should be zero'ed before use
+             */
 } NoffHeader;
diff --git a/code/userprog/synchconsole.cc b/code/userprog/synchconsole.cc
index da76e3c..4f03dfc 100644
--- a/code/userprog/synchconsole.cc
+++ b/code/userprog/synchconsole.cc
@@ -17,7 +17,7 @@
 //              otherwise, read from this file
 //----------------------------------------------------------------------
 
-SynchConsoleInput::SynchConsoleInput(char *inputFile)
+SynchConsoleInput::SynchConsoleInput(char* inputFile)
 {
     consoleInput = new ConsoleInput(inputFile, this);
     lock = new Lock("console in");
@@ -30,9 +30,9 @@ SynchConsoleInput::SynchConsoleInput(char *inputFile)
 //----------------------------------------------------------------------
 
 SynchConsoleInput::~SynchConsoleInput()
-{ 
-    delete consoleInput; 
-    delete lock; 
+{
+    delete consoleInput;
+    delete lock;
     delete waitFor;
 }
 
@@ -73,7 +73,7 @@ SynchConsoleInput::CallBack()
 //              otherwise, read from this file
 //----------------------------------------------------------------------
 
-SynchConsoleOutput::SynchConsoleOutput(char *outputFile)
+SynchConsoleOutput::SynchConsoleOutput(char* outputFile)
 {
     consoleOutput = new ConsoleOutput(outputFile, this);
     lock = new Lock("console out");
@@ -86,9 +86,9 @@ SynchConsoleOutput::SynchConsoleOutput(char *outputFile)
 //----------------------------------------------------------------------
 
 SynchConsoleOutput::~SynchConsoleOutput()
-{ 
-    delete consoleOutput; 
-    delete lock; 
+{
+    delete consoleOutput;
+    delete lock;
     delete waitFor;
 }
 
@@ -106,13 +106,18 @@ SynchConsoleOutput::PutChar(char ch)
     lock->Release();
 }
 
+//----------------------------------------------------------------------
+// SynchConsoleOutput::PutInt
+//      Write a int to the console display, waiting if necessary.
+//----------------------------------------------------------------------
+
 void
 SynchConsoleOutput::PutInt(int value)
 {
-  lock->Acquire();
-  consoleOutput->PutInt(value);
-  waitFor->P();
-  lock->Release();
+    lock->Acquire();
+    consoleOutput->PutInt(value);
+    waitFor->P();
+    lock->Release();
 }
 
 //----------------------------------------------------------------------
diff --git a/code/userprog/synchconsole.h b/code/userprog/synchconsole.h
index 9c2ff47..9dd7865 100644
--- a/code/userprog/synchconsole.h
+++ b/code/userprog/synchconsole.h
@@ -21,34 +21,34 @@
 // a console device
 
 class SynchConsoleInput : public CallBackObj {
-  public:
-    SynchConsoleInput(char *inputFile); // Initialize the console device
-    ~SynchConsoleInput();		// Deallocate console device
+public:
+  SynchConsoleInput(char* inputFile); // Initialize the console device
+  ~SynchConsoleInput();		// Deallocate console device
 
-    char GetChar();		// Read a character, waiting if necessary
-    
-  private:
-    ConsoleInput *consoleInput;	// the hardware keyboard
-    Lock *lock;			// only one reader at a time
-    Semaphore *waitFor;		// wait for callBack
+  char GetChar();		// Read a character, waiting if necessary
 
-    void CallBack();		// called when a keystroke is available
+private:
+  ConsoleInput* consoleInput;	// the hardware keyboard
+  Lock* lock;			// only one reader at a time
+  Semaphore* waitFor;		// wait for callBack
+
+  void CallBack();		// called when a keystroke is available
 };
 
 class SynchConsoleOutput : public CallBackObj {
-  public:
-    SynchConsoleOutput(char *outputFile); // Initialize the console device
-    ~SynchConsoleOutput();
+public:
+  SynchConsoleOutput(char* outputFile); // Initialize the console device
+  ~SynchConsoleOutput();
 
-    void PutChar(char ch);	// Write a character, waiting if necessary
-    void PutInt(int value);
-   
-  private:
-    ConsoleOutput *consoleOutput;// the hardware display
-    Lock *lock;			// only one writer at a time
-    Semaphore *waitFor;		// wait for callBack
+  void PutChar(char ch);	// Write a character, waiting if necessary
+  void PutInt(int value);
 
-    void CallBack();		// called when more data can be written
+private:
+  ConsoleOutput* consoleOutput;// the hardware display
+  Lock* lock;			// only one writer at a time
+  Semaphore* waitFor;		// wait for callBack
+
+  void CallBack();		// called when more data can be written
 };
 
 #endif // SYNCHCONSOLE_H
diff --git a/code/userprog/syscall.h b/code/userprog/syscall.h
index ce6dd48..4f76da2 100644
--- a/code/userprog/syscall.h
+++ b/code/userprog/syscall.h
@@ -1,12 +1,12 @@
-/* syscalls.h 
+/* syscalls.h
  * 	Nachos system call interface.  These are Nachos kernel operations
  * 	that can be invoked from user programs, by trapping to the kernel
  *	via the "syscall" instruction.
  *
- *	This file is included by user programs and by the Nachos kernel. 
+ *	This file is included by user programs and by the Nachos kernel.
  *
  * Copyright (c) 1992-1993 The Regents of the University of California.
- * All rights reserved.  See copyright.h for copyright notice and limitation 
+ * All rights reserved.  See copyright.h for copyright notice and limitation
  * of liability and disclaimer of warranty provisions.
  */
 
@@ -15,83 +15,86 @@
 
 #include "copyright.h"
 #include "errno.h"
-/* system call codes -- used by the stubs to tell the kernel which system call
- * is being asked for
- */
+ /* system call codes -- used by the stubs to tell the kernel which system call
+  * is being asked for
+  */
 #define SC_Halt		0
 #define SC_Exit		1
 #define SC_Exec		2
 #define SC_Join		3
 #define SC_Create	4
-#define SC_Remove 5
+#define SC_Remove       5
 #define SC_Open		6
 #define SC_Read		7
 #define SC_Write	8
-#define SC_Seek   9
-#define SC_Close	      10
-#define SC_ThreadFork	  11
+#define SC_Seek         9
+#define SC_Close	10
+#define SC_ThreadFork	11
 #define SC_ThreadYield	12
-#define SC_ExecV        13
+#define SC_ExecV	13
 #define SC_ThreadExit   14
 #define SC_ThreadJoin   15
-
-#define SC_PrintInt     16
-
-#define SC_Add		      42
-#define SC_MSG	        100
+#define SC_Add		42
+#define SC_MSG		100
+#define SC_PrintInt 16
 
 #ifndef IN_ASM
 
-/* The system call interface.  These are the operations the Nachos
- * kernel needs to support, to be able to run user programs.
- *
- * Each of these is invoked by a user program by simply calling the 
- * procedure; an assembly language stub stuffs the system call code
- * into a register, and traps to the kernel.  The kernel procedures
- * are then invoked in the Nachos kernel, after appropriate error checking, 
- * from the system call entry point in exception.cc.
- */
+  /* The system call interface.  These are the operations the Nachos
+   * kernel needs to support, to be able to run user programs.
+   *
+   * Each of these is invoked by a user program by simply calling the
+   * procedure; an assembly language stub stuffs the system call code
+   * into a register, and traps to the kernel.  The kernel procedures
+   * are then invoked in the Nachos kernel, after appropriate error checking,
+   * from the system call entry point in exception.cc.
+   */
+
+   /* Stop Nachos, and print out performance stats */
+void Halt();
+
+/*
+ * Show the int value on console
+ */
+void PrintInt(int value);
 
-/* Stop Nachos, and print out performance stats */
-void Halt();			
- 
 /*
  * Add the two operants and return the result
- */ 
+ */
 
 int Add(int op1, int op2);
 /*
  * Just for simply showing message, not a safe way for console IO
  */
-void MSG(char *msg);
+void MSG(char* msg);
 
 /* Address space control operations: Exit, Exec, Execv, and Join */
 
 /* This user program is done (status = 0 means exited normally). */
-void Exit(int status);	
+void Exit(int status);
 
 /* A unique identifier for an executing user program (address space) */
-typedef int SpaceId;	
+typedef int SpaceId;
 
 /* A unique identifier for a thread within a task */
 typedef int ThreadId;
 
 /* Run the specified executable, with no args */
 /* This can be implemented as a call to ExecV.
- */ 
+ */
 SpaceId Exec(char* exec_name);
 
 /* Run the executable, stored in the Nachos file "argv[0]", with
- * parameters stored in argv[1..argc-1] and return the 
+ * parameters stored in argv[1..argc-1] and return the
  * address space identifier
  */
 SpaceId ExecV(int argc, char* argv[]);
- 
-/* Only return once the user program "id" has finished.  
+
+/* Only return once the user program "id" has finished.
  * Return the exit status.
  */
-int Join(SpaceId id); 	
- 
+int Join(SpaceId id);
+
 
 /* File system operations: Create, Remove, Open, Read, Write, Close
  * These functions are patterned after UNIX -- files represent
@@ -101,45 +104,45 @@ int Join(SpaceId id);
  * can be used to support these system calls if the regular Nachos
  * file system has not been implemented.
  */
- 
-/* A unique identifier for an open Nachos file. */
-typedef int OpenFileId;	
 
-/* when an address space starts up, it has two open files, representing 
+ /* A unique identifier for an open Nachos file. */
+typedef int OpenFileId;
+
+/* when an address space starts up, it has two open files, representing
  * keyboard input and display output (in UNIX terms, stdin and stdout).
  * Read and Write can be used directly on these, without first opening
  * the console device.
  */
 
 #define SysConsoleInput	0  
-#define SysConsoleOutput 1  
- 
-/* Create a Nachos file, with name "name" */
-/* Note: Create does not open the file.   */
-/* Return 1 on success, negative error code on failure */
-int Create(char *name);
+#define SysConsoleOutput	1  
+
+ /* Create a Nachos file, with name "name" */
+ /* Note: Create does not open the file.   */
+ /* Return 1 on success, negative error code on failure */
+int Create(char* name);
 
 /* Remove a Nachos file, with name "name" */
-int Remove(char *name);
+int Remove(char* name);
 
-/* Open the Nachos file "name", and return an "OpenFileId" that can 
+/* Open the Nachos file "name", and return an "OpenFileId" that can
  * be used to read and write to the file.
  */
-OpenFileId Open(char *name);
+OpenFileId Open(char* name);
 
-/* Write "size" bytes from "buffer" to the open file. 
+/* Write "size" bytes from "buffer" to the open file.
  * Return the number of bytes actually read on success.
  * On failure, a negative error code is returned.
  */
-int Write(char *buffer, int size, OpenFileId id);
+int Write(char* buffer, int size, OpenFileId id);
 
-/* Read "size" bytes from the open file into "buffer".  
+/* Read "size" bytes from the open file into "buffer".
  * Return the number of bytes actually read -- if the open file isn't
- * long enough, or if it is an I/O device, and there aren't enough 
- * characters to read, return whatever is available (for I/O devices, 
+ * long enough, or if it is an I/O device, and there aren't enough
+ * characters to read, return whatever is available (for I/O devices,
  * you should always wait until you can return at least one character).
  */
-int Read(char *buffer, int size, OpenFileId id);
+int Read(char* buffer, int size, OpenFileId id);
 
 /* Set the seek position of the open file "id"
  * to the byte "position".
@@ -153,21 +156,21 @@ int Close(OpenFileId id);
 
 
 /* User-level thread operations: Fork and Yield.  To allow multiple
- * threads to run within a user program. 
+ * threads to run within a user program.
  *
  * Could define other operations, such as LockAcquire, LockRelease, etc.
  */
 
-/* Fork a thread to run a procedure ("func") in the *same* address space 
- * as the current thread.
- * Return a positive ThreadId on success, negative error code on failure
- */
+ /* Fork a thread to run a procedure ("func") in the *same* address space
+  * as the current thread.
+  * Return a positive ThreadId on success, negative error code on failure
+  */
 ThreadId ThreadFork(void (*func)());
 
-/* Yield the CPU to another runnable thread, whether in this address space 
- * or not. 
+/* Yield the CPU to another runnable thread, whether in this address space
+ * or not.
  */
-void ThreadYield();	
+void ThreadYield();
 
 /*
  * Blocks current thread until lokal thread ThreadID exits with ThreadExit.
@@ -180,8 +183,6 @@ int ThreadJoin(ThreadId id);
  */
 void ThreadExit(int ExitCode);
 
-void PrintInt(int number);
-
 #endif /* IN_ASM */
 
 #endif /* SYSCALL_H */
diff --git a/docker-compose.yaml b/docker-compose.yaml
index 06cced5..d4adafa 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -2,6 +2,6 @@
 services:
   test:
     build: .
-    user: '60139:60139'
+    user: ytshih
     volumes:
       - './:/work'