Update README.md

README.md

@@ -12,12 +12,24 @@
 * Added `--open` command-line option to open a file on start
 * Added **Keyboard++**: Enhanced keyboard events
 * Refactored many classes in Kotlin
+* A LOT of [optimizations](https://github.com/hykilpikonna/EMARS#optimizations)
 
 ## FAQ
 
 **How to run:** Install Java JDK >11 and double-click on the jar.  
 **How to compile:** `gradle shadowJar`
 
+## Modifications needed
+
+1. To use **Bitmap Display++**, please add the following code at the end of each render loop:
+
+```asm
+# Tell the display to update
+lw   $t8, ADDR_DISPLAY
+li   $t9, 1
+sw   $t9, 0($t8)
+```
+
 ## Keyboard++
 
 ![Demo](img/bitmap_display_plus_plus.png)
@@ -393,6 +405,25 @@ UNDEFINED      = 0x0
 </details>
 
 
+## Optimizations
+
+In MARS, the BitmapDisplay [re-draws the entire canvas](https://github.com/thomasrussellmurphy/MARS_Assembler/blob/c21dd72e8d2e4a51eb24e276c3f39ef1789148f2/mars/tools/BitmapDisplay.java#L496) instead of only the updated pixels whenever any memory address is updated. This makes updating the display very very very slow, taking 12% of all run time.
+
+![image](https://user-images.githubusercontent.com/22280294/201498543-02a74fb4-9f55-45c8-8eaf-6f1531ab02bd.png)
+
+
+For example, if I loop through the display and change every pixel in my assembly code, the original running time of h∗w will now take h2∗w2, making it take around one second for each update.
+
+Since I can’t easily draw one pixel on update without manual manipulation of AWT Graphics, I changed it so that it treats bit 0 of the memory display as an “update bit,” and only re-draw the screen when the MIPS program sets bit 0 to 1.
+
+After optimizing for this, it runs faster but still not enough for the animation to be smooth. Then, I discovered that most of the running time is used by the backstepper and notifying observers for changes in registers and memory:
+
+![image](https://user-images.githubusercontent.com/22280294/201498548-1e8712ef-79d6-45e9-9d22-096148185c64.png)
+
+
+By default, MARS will store backstep register file copies each time a register is updated, which takes a lot of time since registers are updated very frequently. So I removed backstepping when the execution speed limit is not set. MARS also notifies all memory observers when a program statement instruction is read from memory, which I also removed because nothing uses the notification from reading program statements.
+
+
 ## License
 [MIT][2]. Chech the [LICENSE][3] file. All the credits go to the original developers.
 

build.gradle

@@ -6,6 +6,8 @@ plugins {
     id "com.github.johnrengelman.shadow" version "7.1.2"
 }
 
+version="4.7rc2"
+
 repositories {
     // Use Maven Central for resolving dependencies.
     mavenCentral()

settings.gradle

@@ -1 +1 @@
-rootProject.name = 'MARS'
+rootProject.name = 'EMARS'

src/main/java/mars/MIPSprogram.java

@@ -410,7 +410,7 @@ public class MIPSprogram
     {
         steppedExecution = false;
         Simulator sim = Simulator.getInstance();
-        return sim.simulate(this, RegisterFile.getProgramCounter(), maxSteps, breakPoints, a);
+        return sim.simulate(this, RegisterFile.getPc(), maxSteps, breakPoints, a);
     }
 
 
@@ -426,7 +426,7 @@ public class MIPSprogram
     {
         steppedExecution = true;
         Simulator sim = Simulator.getInstance();
-        boolean done = sim.simulate(this, RegisterFile.getProgramCounter(), 1, null, a);
+        boolean done = sim.simulate(this, RegisterFile.getPc(), 1, null, a);
         return done;
     }
 

src/main/java/mars/MarsLaunch.kt

@@ -669,7 +669,7 @@ class MarsLaunch(var args: Array<String>)
                 {
                     out.print(reg + "\t")
                 }
-                value = RegisterFile.getUserRegister(reg).value
+                value = RegisterFile.getUserRegister(reg)!!.value
                 out.println(formatIntForDisplay(value))
             } else
             {

src/main/java/mars/ProcessingException.java

@@ -79,7 +79,7 @@ public class ProcessingException extends Exception
     {
         errs = new ErrorList();
         errs.add(new ErrorMessage(ps, "Runtime exception at " +
-            Binary.intToHexString(RegisterFile.getProgramCounter() - Instruction.INSTRUCTION_LENGTH) +
+            Binary.intToHexString(RegisterFile.getPc() - Instruction.INSTRUCTION_LENGTH) +
             ": " + m));
         // Stopped using ps.getAddress() because of pseudo-instructions.  All instructions in
         // the macro expansion point to the same ProgramStatement, and thus all will return the

src/main/java/mars/Settings.java

@@ -2,6 +2,7 @@ package mars;
 
 import mars.util.Binary;
 import mars.util.EditorFont;
+import mars.venus.RunSpeedPanel;
 import mars.venus.editors.jeditsyntax.SyntaxStyle;
 import mars.venus.editors.jeditsyntax.SyntaxUtilities;
 
@@ -448,7 +449,7 @@ public class Settings extends Observable
      */
     public boolean getBackSteppingEnabled()
     {
-        return (Globals.program != null && Globals.program.getBackStepper() != null && Globals.program.getBackStepper().enabled());
+        return RunSpeedPanel.getInstance().getRunSpeed() != RunSpeedPanel.UNLIMITED_SPEED;
     }
 
     /**

src/main/java/mars/mips/hardware/Memory.java

@@ -3,7 +3,6 @@ package mars.mips.hardware;
 import mars.Globals;
 import mars.ProgramStatement;
 import mars.Settings;
-import mars.mips.instructions.Instruction;
 import mars.simulator.Exceptions;
 import mars.util.Binary;
 
@@ -571,7 +570,7 @@ public class Memory extends Observable
 
             if (Globals.getSettings().getBooleanSetting(Settings.SELF_MODIFYING_CODE_ENABLED))
             {
-                ProgramStatement oldStatement = getStatementNoNotify(address);
+                ProgramStatement oldStatement = getStatement(address);
                 if (oldStatement != null)
                 {
                     oldValue = oldStatement.getBinaryStatement();
@@ -650,7 +649,7 @@ public class Memory extends Observable
             // DPS adaptation 5-Jul-2013: either throw or call, depending on setting
             if (Globals.getSettings().getBooleanSetting(Settings.SELF_MODIFYING_CODE_ENABLED))
             {
-                ProgramStatement oldStatement = getStatementNoNotify(address);
+                ProgramStatement oldStatement = getStatement(address);
                 if (oldStatement != null)
                 {
                     oldValue = oldStatement.getBinaryStatement();
@@ -861,11 +860,11 @@ public class Memory extends Observable
         }
         else if (inTextSegment(address))
         {
-            // Burch Mod (Jan 2013): replace throw with calls to getStatementNoNotify & getBinaryStatement
+            // Burch Mod (Jan 2013): replace throw with calls to getStatement & getBinaryStatement
             // DPS adaptation 5-Jul-2013: either throw or call, depending on setting
             if (Globals.getSettings().getBooleanSetting(Settings.SELF_MODIFYING_CODE_ENABLED))
             {
-                ProgramStatement stmt = getStatementNoNotify(address);
+                ProgramStatement stmt = getStatement(address);
                 value = stmt == null ? 0 : stmt.getBinaryStatement();
             }
             else
@@ -947,11 +946,11 @@ public class Memory extends Observable
         }
         else if (inTextSegment(address))
         {
-            // Burch Mod (Jan 2013): replace throw with calls to getStatementNoNotify & getBinaryStatement
+            // Burch Mod (Jan 2013): replace throw with calls to getStatement & getBinaryStatement
             // DPS adaptation 5-Jul-2013: either throw or call, depending on setting
             if (Globals.getSettings().getBooleanSetting(Settings.SELF_MODIFYING_CODE_ENABLED))
             {
-                ProgramStatement stmt = getStatementNoNotify(address);
+                ProgramStatement stmt = getStatement(address);
                 value = stmt == null ? 0 : stmt.getBinaryStatement();
             }
             else
@@ -1028,7 +1027,7 @@ public class Memory extends Observable
         {
             try
             {
-                value = (getStatementNoNotify(address) == null) ? null : getStatementNoNotify(address).getBinaryStatement();
+                value = (getStatement(address) == null) ? null : getStatement(address).getBinaryStatement();
             }
             catch (AddressErrorException aee)
             {
@@ -1139,68 +1138,12 @@ public class Memory extends Observable
         return get(address, 1);
     }
 
-    /**
-     * Gets ProgramStatement from Text Segment.
-     *
-     * @param address Starting address of Memory address to be read.  Must be word boundary.
-     * @return reference to ProgramStatement object associated with that address, or null if none.
-     * @throws AddressErrorException If address is not on word boundary or is outside Text Segment.
-     * @see ProgramStatement
-     **/
-
-    public ProgramStatement getStatement(int address) throws AddressErrorException
-    {
-        return getStatement(address, true);
-      	/*
-         if (address % 4 != 0 || !(inTextSegment(address) || inKernelTextSegment(address))) {
-            throw new AddressErrorException(
-               "fetch address for text segment out of range or not aligned to word boundary ",
-               Exceptions.ADDRESS_EXCEPTION_LOAD, address);
-         }
-         if (inTextSegment(address)) {
-            return readProgramStatement(address, textBaseAddress, textBlockTable, true);
-         }
-         else {
-            return readProgramStatement(address, kernelTextBaseAddress, kernelTextBlockTable,true);
-         }
-      	*/
-    }
-
-
     ///////////////////////////////////////////////////////////////////////////
     //  ALL THE OBSERVABLE STUFF GOES HERE.  FOR COMPATIBILITY, Memory IS STILL
     //  EXTENDING OBSERVABLE, BUT WILL NOT USE INHERITED METHODS.  WILL INSTEAD
     //  USE A COLLECTION OF MemoryObserver OBJECTS, EACH OF WHICH IS COMBINATION
     //  OF AN OBSERVER WITH AN ADDRESS RANGE.
-
-    /**
-     * Gets ProgramStatement from Text Segment without notifying observers.
-     *
-     * @param address Starting address of Memory address to be read.  Must be word boundary.
-     * @return reference to ProgramStatement object associated with that address, or null if none.
-     * @throws AddressErrorException If address is not on word boundary or is outside Text Segment.
-     * @see ProgramStatement
-     **/
-
-    public ProgramStatement getStatementNoNotify(int address) throws AddressErrorException
-    {
-        return getStatement(address, false);
-      	/*
-         if (address % 4 != 0 || !(inTextSegment(address) || inKernelTextSegment(address))) {
-            throw new AddressErrorException(
-               "fetch address for text segment out of range or not aligned to word boundary ",
-               Exceptions.ADDRESS_EXCEPTION_LOAD, address);
-         }
-         if (inTextSegment(address)) {
-            return readProgramStatement(address, textBaseAddress, textBlockTable, false);
-         }
-         else {
-            return readProgramStatement(address, kernelTextBaseAddress, kernelTextBlockTable, false);
-         }
-      	*/
-    }
-
-    private ProgramStatement getStatement(int address, boolean notify) throws AddressErrorException
+    public ProgramStatement getStatement(int address) throws AddressErrorException
     {
         if (!wordAligned(address))
         {
@@ -1217,11 +1160,11 @@ public class Memory extends Observable
         }
         if (inTextSegment(address))
         {
-            return readProgramStatement(address, textBaseAddress, textBlockTable, notify);
+            return readProgramStatement(address, textBaseAddress, textBlockTable);
         }
         else if (inKernelTextSegment(address))
         {
-            return readProgramStatement(address, kernelTextBaseAddress, kernelTextBlockTable, notify);
+            return readProgramStatement(address, kernelTextBaseAddress, kernelTextBlockTable);
         }
         else
         {
@@ -1601,7 +1544,7 @@ public class Memory extends Observable
     // as valid.  It may be either in user or kernel text segment, as specified by arguments.
     // Returns associated ProgramStatement or null if none.
     // Last parameter controls whether or not observers will be notified.
-    private ProgramStatement readProgramStatement(int address, int baseAddress, ProgramStatement[][] blockTable, boolean notify)
+    private ProgramStatement readProgramStatement(int address, int baseAddress, ProgramStatement[][] blockTable)
     {
         int relative = (address - baseAddress) >> 2; // convert byte address to words
         int block = relative / TEXT_BLOCK_LENGTH_WORDS;
@@ -1611,25 +1554,13 @@ public class Memory extends Observable
             if (blockTable[block] == null || blockTable[block][offset] == null)
             {
                 // No instructions are stored in this block or offset.
-                if (notify)
-                {
-                    notifyAnyObservers(AccessNotice.READ, address, Instruction.INSTRUCTION_LENGTH, 0);
-                }
                 return null;
             }
             else
             {
-                if (notify)
-                {
-                    notifyAnyObservers(AccessNotice.READ, address, Instruction.INSTRUCTION_LENGTH, blockTable[block][offset].getBinaryStatement());
-                }
                 return blockTable[block][offset];
             }
         }
-        if (notify)
-        {
-            notifyAnyObservers(AccessNotice.READ, address, Instruction.INSTRUCTION_LENGTH, 0);
-        }
         return null;
     }
 

src/main/java/mars/mips/hardware/Register.java

@@ -45,7 +45,7 @@ public class Register extends Observable
 
     private int resetValue;
 
-    // volatile should be enough to allow safe multi-threaded access
+    // volatile should be enough to allow safe multithreaded access
     // w/o the use of synchronized methods.  getValue and setValue
     // are the only methods here used by the register collection
     // (RegisterFile, Coprocessor0, Coprocessor1) methods.
@@ -85,19 +85,6 @@ public class Register extends Observable
      */
 
     public synchronized int getValue()
-    {
-        notifyAnyObservers(AccessNotice.READ);
-        return value;
-    }
-
-
-    /**
-     * Returns the value of the Register.  Observers are not notified. Added for release 3.8.
-     *
-     * @return value The value of the Register.
-     */
-
-    public synchronized int getValueNoNotify()
     {
         return value;
     }
@@ -136,7 +123,6 @@ public class Register extends Observable
     {
         int old = value;
         value = val;
-        notifyAnyObservers(AccessNotice.WRITE);
         return old;
     }
 
@@ -157,18 +143,4 @@ public class Register extends Observable
     {
         resetValue = reset;
     }
-
-    //
-    // Method to notify any observers of register operation that has just occurred.
-    //
-    private void notifyAnyObservers(int type)
-    {
-        if (this.countObservers() > 0)
-        {// && Globals.program != null) && Globals.program.inSteppedExecution()) {
-            this.setChanged();
-            this.notifyObservers(new RegisterAccessNotice(type, this.name));
-        }
-    }
-
-
 }

src/main/java/mars/mips/hardware/RegisterFile.java

@@ -1,395 +0,0 @@
-package mars.mips.hardware;
-
-import mars.Globals;
-import mars.assembler.SymbolTable;
-import mars.mips.instructions.Instruction;
-import mars.util.Binary;
-
-import java.util.Observer;
-
-/*
-Copyright (c) 2003-2008,  Pete Sanderson and Kenneth Vollmar
-
-Developed by Pete Sanderson (psanderson@otterbein.edu)
-and Kenneth Vollmar (kenvollmar@missouristate.edu)
-
-Permission is hereby granted, free of charge, to any person obtaining 
-a copy of this software and associated documentation files (the 
-"Software"), to deal in the Software without restriction, including 
-without limitation the rights to use, copy, modify, merge, publish, 
-distribute, sublicense, and/or sell copies of the Software, and to 
-permit persons to whom the Software is furnished to do so, subject 
-to the following conditions:
-
-The above copyright notice and this permission notice shall be 
-included in all copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
-EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
-MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
-IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR 
-ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF 
-CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION 
-WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-
-(MIT license, http://www.opensource.org/licenses/mit-license.html)
- */
-
-/**
- * Represents the collection of MIPS registers.
- *
- * @author Jason Bumgarner, Jason Shrewsbury
- * @version June 2003
- **/
-
-public class RegisterFile
-{
-
-    public static final int GLOBAL_POINTER_REGISTER = 28;
-
-    public static final int STACK_POINTER_REGISTER = 29;
-
-    private static final Register[] regFile =
-        {new Register("$zero", 0, 0), new Register("$at", 1, 0),
-            new Register("$v0", 2, 0), new Register("$v1", 3, 0),
-            new Register("$a0", 4, 0), new Register("$a1", 5, 0),
-            new Register("$a2", 6, 0), new Register("$a3", 7, 0),
-            new Register("$t0", 8, 0), new Register("$t1", 9, 0),
-            new Register("$t2", 10, 0), new Register("$t3", 11, 0),
-            new Register("$t4", 12, 0), new Register("$t5", 13, 0),
-            new Register("$t6", 14, 0), new Register("$t7", 15, 0),
-            new Register("$s0", 16, 0), new Register("$s1", 17, 0),
-            new Register("$s2", 18, 0), new Register("$s3", 19, 0),
-            new Register("$s4", 20, 0), new Register("$s5", 21, 0),
-            new Register("$s6", 22, 0), new Register("$s7", 23, 0),
-            new Register("$t8", 24, 0), new Register("$t9", 25, 0),
-            new Register("$k0", 26, 0), new Register("$k1", 27, 0),
-            new Register("$gp", GLOBAL_POINTER_REGISTER, Memory.globalPointer),
-            new Register("$sp", STACK_POINTER_REGISTER, Memory.stackPointer),
-            new Register("$fp", 30, 0), new Register("$ra", 31, 0)
-        };
-
-    private static final Register programCounter = new Register("pc", 32, Memory.textBaseAddress);
-
-    private static final Register hi = new Register("hi", 33, 0);//this is an internal register with arbitrary number
-
-    private static final Register lo = new Register("lo", 34, 0);// this is an internal register with arbitrary number
-
-
-    /**
-     * Method for displaying the register values for debugging.
-     **/
-
-    public static void showRegisters()
-    {
-        for (int i = 0; i < regFile.length; i++)
-        {
-            System.out.println("Name: " + regFile[i].getName());
-            System.out.println("Number: " + regFile[i].getNumber());
-            System.out.println("Value: " + regFile[i].getValue());
-            System.out.println();
-        }
-    }
-
-
-    /**
-     * This method updates the register value who's number is num.  Also handles the lo and hi registers
-     *
-     * @param num Register to set the value of.
-     * @param val The desired value for the register.
-     **/
-
-    public static int updateRegister(int num, int val)
-    {
-        int old = 0;
-        if (num == 0)
-        {
-            //System.out.println("You can not change the value of the zero register.");
-        }
-        else
-        {
-            for (int i = 0; i < regFile.length; i++)
-            {
-                if (regFile[i].getNumber() == num)
-                {
-                    old = (Globals.getSettings().getBackSteppingEnabled())
-                        ? Globals.program.getBackStepper().addRegisterFileRestore(num, regFile[i].setValue(val))
-                        : regFile[i].setValue(val);
-                    break;
-                }
-            }
-        }
-        if (num == 33)
-        {//updates the hi register
-            old = (Globals.getSettings().getBackSteppingEnabled())
-                ? Globals.program.getBackStepper().addRegisterFileRestore(num, hi.setValue(val))
-                : hi.setValue(val);
-        }
-        else if (num == 34)
-        {// updates the low register
-            old = (Globals.getSettings().getBackSteppingEnabled())
-                ? Globals.program.getBackStepper().addRegisterFileRestore(num, lo.setValue(val))
-                : lo.setValue(val);
-        }
-        return old;
-    }
-
-    /**
-     * Sets the value of the register given to the value given.
-     *
-     * @param reg Name of register to set the value of.
-     * @param val The desired value for the register.
-     **/
-
-    public static void updateRegister(String reg, int val)
-    {
-        if (reg.equals("zero"))
-        {
-            //System.out.println("You can not change the value of the zero register.");
-        }
-        else
-        {
-            for (int i = 0; i < regFile.length; i++)
-            {
-                if (regFile[i].getName().equals(reg))
-                {
-                    updateRegister(i, val);
-                    break;
-                }
-            }
-        }
-    }
-
-    /**
-     * Returns the value of the register who's number is num.
-     *
-     * @param num The register number.
-     * @return The value of the given register.
-     **/
-
-    public static int getValue(int num)
-    {
-        if (num == 33)
-        {
-            return hi.getValue();
-        }
-        else if (num == 34)
-        {
-            return lo.getValue();
-        }
-        else
-        {
-            return regFile[num].getValue();
-        }
-
-    }
-
-    /**
-     * For getting the number representation of the register.
-     *
-     * @param n The string formatted register name to look for.
-     * @return The number of the register represented by the string or -1 if no match.
-     **/
-
-    public static int getNumber(String n)
-    {
-        int j = -1;
-        for (int i = 0; i < regFile.length; i++)
-        {
-            if (regFile[i].getName().equals(n))
-            {
-                j = regFile[i].getNumber();
-                break;
-            }
-        }
-        return j;
-    }
-
-    /**
-     * For returning the set of registers.
-     *
-     * @return The set of registers.
-     **/
-
-    public static Register[] getRegisters()
-    {
-        return regFile;
-    }
-
-    /**
-     * Get register object corresponding to given name.  If no match, return null.
-     *
-     * @param Rname The register name, either in $0 or $zero format.
-     * @return The register object,or null if not found.
-     **/
-
-    public static Register getUserRegister(String Rname)
-    {
-        Register reg = null;
-        if (Rname.charAt(0) == '$')
-        {
-            try
-            {
-                // check for register number 0-31.
-                reg = regFile[Binary.stringToInt(Rname.substring(1))];    // KENV 1/6/05
-            }
-            catch (Exception e)
-            {
-                // handles both NumberFormat and ArrayIndexOutOfBounds
-                // check for register mnemonic $zero thru $ra
-                reg = null; // just to be sure
-                // just do linear search; there aren't that many registers
-                for (int i = 0; i < regFile.length; i++)
-                {
-                    if (Rname.equals(regFile[i].getName()))
-                    {
-                        reg = regFile[i];
-                        break;
-                    }
-                }
-            }
-        }
-        return reg;
-    }
-
-    /**
-     * For initializing the Program Counter.  Do not use this to implement jumps and branches, as it will NOT record a
-     * backstep entry with the restore value. If you need backstepping capability, use setProgramCounter instead.
-     *
-     * @param value The value to set the Program Counter to.
-     **/
-
-    public static void initializeProgramCounter(int value)
-    {
-        programCounter.setValue(value);
-    }
-
-    /**
-     * Will initialize the Program Counter to either the default reset value, or the address associated with source
-     * program global label "main", if it exists as a text segment label and the global setting is set.
-     *
-     * @param startAtMain If true, will set program counter to address of statement labeled 'main' (or other defined
-     *     start label) if defined.  If not defined, or if parameter false, will set program counter to default reset
-     *     value.
-     **/
-
-    public static void initializeProgramCounter(boolean startAtMain)
-    {
-        int mainAddr = Globals.symbolTable.getAddress(SymbolTable.getStartLabel());
-        if (startAtMain && mainAddr != SymbolTable.NOT_FOUND && (Memory.inTextSegment(mainAddr) || Memory.inKernelTextSegment(mainAddr)))
-        {
-            initializeProgramCounter(mainAddr);
-        }
-        else
-        {
-            initializeProgramCounter(programCounter.getResetValue());
-        }
-    }
-
-    /**
-     * For setting the Program Counter.  Note that ordinary PC update should be done using incrementPC() method. Use
-     * this only when processing jumps and branches.
-     *
-     * @param value The value to set the Program Counter to.
-     * @return previous PC value
-     **/
-
-    public static int setProgramCounter(int value)
-    {
-        int old = programCounter.getValue();
-        programCounter.setValue(value);
-        if (Globals.getSettings().getBackSteppingEnabled())
-        {
-            Globals.program.getBackStepper().addPCRestore(old);
-        }
-        return old;
-    }
-
-    /**
-     * For returning the program counters value.
-     *
-     * @return The program counters value as an int.
-     **/
-
-    public static int getProgramCounter()
-    {
-        return programCounter.getValue();
-    }
-
-    /**
-     * Returns Register object for program counter.  Use with caution.
-     *
-     * @return program counter's Register object.
-     */
-    public static Register getProgramCounterRegister()
-    {
-        return programCounter;
-    }
-
-    /**
-     * For returning the program counter's initial (reset) value.
-     *
-     * @return The program counter's initial value
-     **/
-
-    public static int getInitialProgramCounter()
-    {
-        return programCounter.getResetValue();
-    }
-
-    /**
-     * Method to reinitialize the values of the registers.
-     * <b>NOTE:</b> Should <i>not</i> be called from command-mode MARS because this
-     * this method uses global settings from the registry.  Command-mode must operate using only the command switches,
-     * not registry settings.  It can be called from tools running stand-alone, and this is done in
-     * <code>AbstractMarsToolAndApplication</code>.
-     **/
-
-    public static void resetRegisters()
-    {
-        for (int i = 0; i < regFile.length; i++)
-        {
-            regFile[i].resetValue();
-        }
-        initializeProgramCounter(Globals.getSettings().getStartAtMain());// replaces "programCounter.resetValue()", DPS 3/3/09
-        hi.resetValue();
-        lo.resetValue();
-    }
-
-    /**
-     * Method to increment the Program counter in the general case (not a jump or branch).
-     **/
-
-    public static void incrementPC()
-    {
-        programCounter.setValue(programCounter.getValue() + Instruction.INSTRUCTION_LENGTH);
-    }
-
-    /**
-     * Each individual register is a separate object and Observable.  This handy method will add the given Observer to
-     * each one.  Currently does not apply to Program Counter.
-     */
-    public static void addRegistersObserver(Observer observer)
-    {
-        for (int i = 0; i < regFile.length; i++)
-        {
-            regFile[i].addObserver(observer);
-        }
-        hi.addObserver(observer);
-        lo.addObserver(observer);
-    }
-
-    /**
-     * Each individual register is a separate object and Observable.  This handy method will delete the given Observer
-     * from each one.  Currently does not apply to Program Counter.
-     */
-    public static void deleteRegistersObserver(Observer observer)
-    {
-        for (int i = 0; i < regFile.length; i++)
-        {
-            regFile[i].deleteObserver(observer);
-        }
-        hi.deleteObserver(observer);
-        lo.deleteObserver(observer);
-    }
-}

src/main/java/mars/mips/hardware/RegisterFile.kt

@@ -0,0 +1,310 @@
+package mars.mips.hardware
+
+import mars.Globals
+import mars.assembler.SymbolTable
+import mars.mips.instructions.Instruction
+import mars.util.Binary
+import java.util.*
+
+/*
+Copyright (c) 2003-2008,  Pete Sanderson and Kenneth Vollmar
+
+Developed by Pete Sanderson (psanderson@otterbein.edu)
+and Kenneth Vollmar (kenvollmar@missouristate.edu)
+
+Permission is hereby granted, free of charge, to any person obtaining 
+a copy of this software and associated documentation files (the 
+"Software"), to deal in the Software without restriction, including 
+without limitation the rights to use, copy, modify, merge, publish, 
+distribute, sublicense, and/or sell copies of the Software, and to 
+permit persons to whom the Software is furnished to do so, subject 
+to the following conditions:
+
+The above copyright notice and this permission notice shall be 
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR 
+ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF 
+CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION 
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+(MIT license, http://www.opensource.org/licenses/mit-license.html)
+ */
+/**
+ * Represents the collection of MIPS registers.
+ *
+ * @author Jason Bumgarner, Jason Shrewsbury
+ * @version June 2003
+ */
+object RegisterFile
+{
+    const val GLOBAL_POINTER_REGISTER = 28
+    const val STACK_POINTER_REGISTER = 29
+
+    /**
+     * For returning the set of registers.
+     *
+     * @return The set of registers.
+     */
+    @JvmStatic
+    val registers = arrayOf(
+        Register("\$zero", 0, 0), Register("\$at", 1, 0),
+        Register("\$v0", 2, 0), Register("\$v1", 3, 0),
+        Register("\$a0", 4, 0), Register("\$a1", 5, 0),
+        Register("\$a2", 6, 0), Register("\$a3", 7, 0),
+        Register("\$t0", 8, 0), Register("\$t1", 9, 0),
+        Register("\$t2", 10, 0), Register("\$t3", 11, 0),
+        Register("\$t4", 12, 0), Register("\$t5", 13, 0),
+        Register("\$t6", 14, 0), Register("\$t7", 15, 0),
+        Register("\$s0", 16, 0), Register("\$s1", 17, 0),
+        Register("\$s2", 18, 0), Register("\$s3", 19, 0),
+        Register("\$s4", 20, 0), Register("\$s5", 21, 0),
+        Register("\$s6", 22, 0), Register("\$s7", 23, 0),
+        Register("\$t8", 24, 0), Register("\$t9", 25, 0),
+        Register("\$k0", 26, 0), Register("\$k1", 27, 0),
+        Register("\$gp", GLOBAL_POINTER_REGISTER, Memory.globalPointer),
+        Register("\$sp", STACK_POINTER_REGISTER, Memory.stackPointer),
+        Register("\$fp", 30, 0), Register("\$ra", 31, 0),  // Internal registers
+        Register("pc", 32, Memory.textBaseAddress),
+        Register("hi", 33, 0),
+        Register("lo", 34, 0)
+    )
+
+    val registerNameIndex = registers.associateBy { it.name }
+
+    @JvmStatic
+    val programCounterRegister = registers[32]
+    @JvmStatic
+    private val HI = registers[33]
+    @JvmStatic
+    private val LO = registers[34]
+
+    val backstep by lazy { Globals.getSettings().backSteppingEnabled }
+
+    /**
+     * Method for displaying the register values for debugging.
+     */
+    @JvmStatic
+    fun showRegisters()
+    {
+        for (register in registers)
+        {
+            println("Name: " + register.name)
+            println("Number: " + register.number)
+            println("Value: " + register.value)
+            println()
+        }
+    }
+
+    /**
+     * This method updates the register value who's number is num.  Also handles the lo and hi registers
+     *
+     * @param num Register to set the value of.
+     * @param value The desired value for the register.
+     */
+    @JvmStatic
+    fun updateRegister(num: Int, value: Int): Int
+    {
+        val old = 0
+        if (num == 0)
+        {
+            println("You can not change the value of the zero register.")
+        }
+        else
+        {
+            registers[num].value = value
+        }
+        return old
+    }
+
+    /**
+     * Sets the value of the register given to the value given.
+     *
+     * @param reg Name of register to set the value of.
+     * @param value The desired value for the register.
+     */
+    @JvmStatic
+    fun updateRegister(reg: String, value: Int)
+    {
+        registerNameIndex[reg]?.let {
+            updateRegister(it.number, value)
+        }
+    }
+
+    /**
+     * Returns the value of the register who's number is num.
+     *
+     * @param num The register number.
+     * @return The value of the given register.
+     */
+    @JvmStatic
+    fun getValue(num: Int) = registers[num].value
+
+    /**
+     * For getting the number representation of the register.
+     *
+     * @param n The string formatted register name to look for.
+     * @return The number of the register represented by the string or -1 if no match.
+     */
+    @JvmStatic
+    fun getNumber(n: String) = registerNameIndex[n]?.number ?: -1
+
+    /**
+     * Get register object corresponding to given name.  If no match, return null.
+     *
+     * @param Rname The register name, either in $0 or $zero format.
+     * @return The register object,or null if not found.
+     */
+    @JvmStatic
+    fun getUserRegister(Rname: String): Register?
+    {
+        var reg: Register? = null
+        if (Rname[0] == '$')
+        {
+            try
+            {
+                // check for register number 0-31.
+                reg = registers[Binary.stringToInt(Rname.substring(1))] // KENV 1/6/05
+            } catch (e: Exception)
+            {
+                // handles both NumberFormat and ArrayIndexOutOfBounds
+                // check for register mnemonic $zero thru $ra
+                reg = null // just to be sure
+                // just do linear search; there aren't that many registers
+                var i = 0
+                while (i < registers.size)
+                {
+                    if (Rname == registers[i].name)
+                    {
+                        reg = registers[i]
+                        break
+                    }
+                    i++
+                }
+            }
+        }
+        return reg
+    }
+
+    /**
+     * For initializing the Program Counter.  Do not use this to implement jumps and branches, as it will NOT record a
+     * backstep entry with the restore value. If you need backstepping capability, use setProgramCounter instead.
+     *
+     * @param value The value to set the Program Counter to.
+     */
+    @JvmStatic
+    fun initializeProgramCounter(value: Int)
+    {
+        programCounterRegister.value = value
+    }
+
+    /**
+     * Will initialize the Program Counter to either the default reset value, or the address associated with source
+     * program global label "main", if it exists as a text segment label and the global setting is set.
+     *
+     * @param startAtMain If true, will set program counter to address of statement labeled 'main' (or other defined
+     * start label) if defined.  If not defined, or if parameter false, will set program counter to default reset
+     * value.
+     */
+    fun initializeProgramCounter(startAtMain: Boolean)
+    {
+        val mainAddr = Globals.symbolTable.getAddress(SymbolTable.getStartLabel())
+        if (startAtMain && mainAddr != SymbolTable.NOT_FOUND && (Memory.inTextSegment(mainAddr) || Memory.inKernelTextSegment(
+                mainAddr
+            ))
+        )
+        {
+            initializeProgramCounter(mainAddr)
+        } else
+        {
+            initializeProgramCounter(programCounterRegister.resetValue)
+        }
+    }
+
+    /**
+     * For setting the Program Counter.  Note that ordinary PC update should be done using incrementPC() method. Use
+     * this only when processing jumps and branches.
+     *
+     * @param value The value to set the Program Counter to.
+     * @return previous PC value
+     */
+    @JvmStatic
+    fun setProgramCounter(value: Int): Int
+    {
+        val old = programCounterRegister.value
+        programCounterRegister.value = value
+        if (Globals.getSettings().backSteppingEnabled)
+        {
+            Globals.program.backStepper.addPCRestore(old)
+        }
+        return old
+    }
+
+    /**
+     * For returning the program counters value.
+     *
+     * @return The program counters value as an int.
+     */
+    @JvmStatic
+    val pc: Int
+        get() = programCounterRegister.value
+
+    /**
+     * For returning the program counter's initial (reset) value.
+     *
+     * @return The program counter's initial value
+     */
+    val initialProgramCounter: Int
+        get() = programCounterRegister.resetValue
+
+    /**
+     * Method to reinitialize the values of the registers.
+     * **NOTE:** Should *not* be called from command-mode MARS because this
+     * this method uses global settings from the registry.  Command-mode must operate using only the command switches,
+     * not registry settings.  It can be called from tools running stand-alone, and this is done in
+     * `AbstractMarsToolAndApplication`.
+     */
+    @JvmStatic
+    fun resetRegisters()
+    {
+        for (i in registers.indices)
+        {
+            registers[i].resetValue()
+        }
+        initializeProgramCounter(Globals.getSettings().startAtMain) // replaces "programCounter.resetValue()", DPS 3/3/09
+        HI.resetValue()
+        LO.resetValue()
+    }
+
+    /**
+     * Method to increment the Program counter in the general case (not a jump or branch).
+     */
+    @JvmStatic
+    fun incrementPC()
+    {
+        programCounterRegister.value += Instruction.INSTRUCTION_LENGTH
+    }
+
+    /**
+     * Each individual register is a separate object and Observable.  This handy method will add the given Observer to
+     * each one.  Currently does not apply to Program Counter.
+     */
+    @JvmStatic
+    fun addRegistersObserver(observer: Observer?)
+    {
+        registers.filter { it.number != 32 }.forEach { it.addObserver(observer) }
+    }
+
+    /**
+     * Each individual register is a separate object and Observable.  This handy method will delete the given Observer
+     * from each one.  Currently does not apply to Program Counter.
+     */
+    @JvmStatic
+    fun deleteRegistersObserver(observer: Observer?)
+    {
+        registers.filter { it.number != 32 }.forEach { it.deleteObserver(observer) }
+    }
+}

src/main/java/mars/mips/instructions/InstructionSet.java

@@ -1239,7 +1239,7 @@ public class InstructionSet
                     {
                         int[] operands = statement.getOperands();
                         processJump(
-                            ((RegisterFile.getProgramCounter() & 0xF0000000)
+                            ((RegisterFile.getPc() & 0xF0000000)
                                 | (operands[0] << 2)));
                     }
                 }));
@@ -1268,7 +1268,7 @@ public class InstructionSet
                         int[] operands = statement.getOperands();
                         processReturnAddress(31);// RegisterFile.updateRegister(31, RegisterFile.getProgramCounter());
                         processJump(
-                            (RegisterFile.getProgramCounter() & 0xF0000000)
+                            (RegisterFile.getPc() & 0xF0000000)
                                 | (operands[0] << 2));
                     }
                 }));
@@ -3442,13 +3442,13 @@ public class InstructionSet
         if (Globals.getSettings().getDelayedBranchingEnabled())
         {
             // Register the branch target address (absolute byte address).
-            DelayedBranch.register(RegisterFile.getProgramCounter() + (displacement << 2));
+            DelayedBranch.register(RegisterFile.getPc() + (displacement << 2));
         }
         else
         {
             // Decrement needed because PC has already been incremented
             RegisterFile.setProgramCounter(
-                RegisterFile.getProgramCounter()
+                RegisterFile.getPc()
                     + (displacement << 2)); // - Instruction.INSTRUCTION_LENGTH);
         }
     }
@@ -3489,7 +3489,7 @@ public class InstructionSet
 
     private void processReturnAddress(int register)
     {
-        RegisterFile.updateRegister(register, RegisterFile.getProgramCounter() +
+        RegisterFile.updateRegister(register, RegisterFile.getPc() +
             ((Globals.getSettings().getDelayedBranchingEnabled()) ?
                 Instruction.INSTRUCTION_LENGTH : 0));
     }

src/main/java/mars/simulator/BackStepper.java

@@ -222,7 +222,7 @@ public class BackStepper
     private int pc()
     {
         // PC incremented prior to instruction simulation, so need to adjust for that.
-        return RegisterFile.getProgramCounter() - Instruction.INSTRUCTION_LENGTH;
+        return RegisterFile.getPc() - Instruction.INSTRUCTION_LENGTH;
     }
 
     /**
@@ -406,7 +406,7 @@ public class BackStepper
                 // Client does not have direct access to program statement, and rather than making all
                 // of them go through the methods below to obtain it, we will do it here.
                 // Want the program statement but do not want observers notified.
-                ps = Globals.memory.getStatementNoNotify(programCounter);
+                ps = Globals.memory.getStatement(programCounter);
             }
             catch (Exception e)
             {

src/main/java/mars/simulator/Exceptions.java

@@ -88,7 +88,7 @@ public class Exceptions
         // identify devices for External Interrupt (8=keyboard,9=display).
         Coprocessor0.updateRegister(Coprocessor0.CAUSE, (Coprocessor0.getValue(Coprocessor0.CAUSE) & 0xFFFFFC83 | (cause << 2)));
         // When exception occurred, PC had already been incremented so need to subtract 4 here.
-        Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getProgramCounter() - Instruction.INSTRUCTION_LENGTH);
+        Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getPc() - Instruction.INSTRUCTION_LENGTH);
         // Set EXL (Exception Level) bit, bit position 1, in STATUS register to 1.
         Coprocessor0.updateRegister(Coprocessor0.STATUS, Binary.setBit(Coprocessor0.getValue(Coprocessor0.STATUS), Coprocessor0.EXCEPTION_LEVEL));
     }

src/main/java/mars/simulator/Simulator.java

@@ -319,18 +319,18 @@ public class Simulator extends Observable
             ProgramStatement statement = null;
             try
             {
-                statement = Globals.memory.getStatement(RegisterFile.getProgramCounter());
+                statement = Globals.memory.getStatement(RegisterFile.getPc());
             }
             catch (AddressErrorException e)
             {
                 ErrorList el = new ErrorList();
-                el.add(new ErrorMessage((MIPSprogram) null, 0, 0, "invalid program counter value: " + Binary.intToHexString(RegisterFile.getProgramCounter())));
+                el.add(new ErrorMessage((MIPSprogram) null, 0, 0, "invalid program counter value: " + Binary.intToHexString(RegisterFile.getPc())));
                 this.pe = new ProcessingException(el, e);
                 // Next statement is a hack.  Previous statement sets EPC register to ProgramCounter-4
                 // because it assumes the bad address comes from an operand so the ProgramCounter has already been
                 // incremented.  In this case, bad address is the instruction fetch itself so Program Counter has
                 // not yet been incremented.  We'll set the EPC directly here.  DPS 8-July-2013
-                Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getProgramCounter());
+                Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getPc());
                 this.constructReturnReason = EXCEPTION;
                 this.done = true;
                 SystemIO.resetFiles(); // close any files opened in MIPS program
@@ -373,7 +373,7 @@ public class Simulator extends Observable
 
             while (statement != null)
             {
-                pc = RegisterFile.getProgramCounter(); // added: 7/26/06 (explanation above)
+                pc = RegisterFile.getPc(); // added: 7/26/06 (explanation above)
                 RegisterFile.incrementPC();
                 // Perform the MIPS instruction in synchronized block.  If external threads agree
                 // to access MIPS memory and registers only through synchronized blocks on same
@@ -469,7 +469,7 @@ public class Simulator extends Observable
                 }
                 //	Return if we've reached a breakpoint.
                 if ((breakPoints != null) &&
-                    (Arrays.binarySearch(breakPoints, RegisterFile.getProgramCounter()) >= 0))
+                    (Arrays.binarySearch(breakPoints, RegisterFile.getPc()) >= 0))
                 {
                     this.constructReturnReason = BREAKPOINT;
                     this.done = false;
@@ -518,18 +518,18 @@ public class Simulator extends Observable
 
                 try
                 {
-                    statement = Globals.memory.getStatement(RegisterFile.getProgramCounter());
+                    statement = Globals.memory.getStatement(RegisterFile.getPc());
                 }
                 catch (AddressErrorException e)
                 {
                     ErrorList el = new ErrorList();
-                    el.add(new ErrorMessage((MIPSprogram) null, 0, 0, "invalid program counter value: " + Binary.intToHexString(RegisterFile.getProgramCounter())));
+                    el.add(new ErrorMessage((MIPSprogram) null, 0, 0, "invalid program counter value: " + Binary.intToHexString(RegisterFile.getPc())));
                     this.pe = new ProcessingException(el, e);
                     // Next statement is a hack.  Previous statement sets EPC register to ProgramCounter-4
                     // because it assumes the bad address comes from an operand so the ProgramCounter has already been
                     // incremented.  In this case, bad address is the instruction fetch itself so Program Counter has
                     // not yet been incremented.  We'll set the EPC directly here.  DPS 8-July-2013
-                    Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getProgramCounter());
+                    Coprocessor0.updateRegister(Coprocessor0.EPC, RegisterFile.getPc());
                     this.constructReturnReason = EXCEPTION;
                     this.done = true;
                     SystemIO.resetFiles(); // close any files opened in MIPS program

src/main/java/mars/tools/BHTSimulator.java

@@ -365,7 +365,7 @@ public class BHTSimulator extends AbstractMarsToolAndApplication implements Acti
             try
             {
                 // access the statement in the text segment without notifying other tools etc.
-                ProgramStatement stmt = Memory.getInstance().getStatementNoNotify(memAccNotice.getAddress());
+                ProgramStatement stmt = Memory.getInstance().getStatement(memAccNotice.getAddress());
 
                 // necessary to handle possible null pointers at the end of the program
                 // (e.g., if the simulator tries to execute the next instruction after the last instruction in the text segment)

src/main/java/mars/tools/BitmapDisplay.kt

@@ -13,7 +13,6 @@ import java.util.*
 import javax.swing.*
 import javax.swing.border.EmptyBorder
 import kotlin.collections.ArrayList
-import kotlin.collections.HashMap
 import kotlin.collections.HashSet
 
 /*
@@ -51,10 +50,6 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 class BitmapDisplay : AbstractMarsToolAndApplication
 {
     // Major GUI components
-    private lateinit var uiUnitWidthSelector: JComboBox<Int>
-    private lateinit var uiUnitHeightSelector: JComboBox<Int>
-    private lateinit var uiWidthSelector: JComboBox<Int>
-    private lateinit var uiHeightSelector: JComboBox<Int>
     private lateinit var uiBaseAddressSelector: JComboBox<String>
     private lateinit var uiKeyboardCheckbox: JCheckBox
     private lateinit var canvas: JPanel
@@ -65,10 +60,10 @@ class BitmapDisplay : AbstractMarsToolAndApplication
     private val backgroundColor = Color.WHITE
 
     // Values for display canvas.  Note their initialization uses the identifiers just above.
-    private val unitWidth get() = uiUnitWidthSelector.getInt()
-    private val unitHeight get() = uiUnitHeightSelector.getInt()
-    private val displayWidth get() = uiWidthSelector.getInt()
-    private val displayHeight get() = uiHeightSelector.getInt()
+    private var unitWidth: Int = 2
+    private var unitHeight: Int = 2
+    private var displayWidth: Int = 512
+    private var displayHeight: Int = 256
     private val displayDimension get() = Dimension(displayWidth, displayHeight)
 
     private val baseAddresses = intArrayOf(Memory.dataSegmentBaseAddress, Memory.globalPointer, Memory.dataBaseAddress,
@@ -78,6 +73,7 @@ class BitmapDisplay : AbstractMarsToolAndApplication
 
     // Keyboard++
     private var keyboardAddr: UInt = 0xFFFF0010u
+    private var displayUpdateAddr: UInt = 0xFFFF0008u
     private var keyboardAttached = false
     private lateinit var uiKeyboard: JTextField
 
@@ -180,7 +176,17 @@ class BitmapDisplay : AbstractMarsToolAndApplication
         }
 
         // For the display
-        updateColorForAddress(ac)
+        val value = ac.value
+        val offset = ((addr - baseAddress.toUInt()) / 4u).toInt()
+        try
+        {
+            grid.setElement(offset / grid.cols, offset % grid.cols, value)
+        }
+        catch (e: IndexOutOfBoundsException)
+        {
+            // If address is out of range for display, do nothing.
+        }
+        if (offset == 0) canvas.repaint()
     }
 
     /**
@@ -239,17 +245,10 @@ class BitmapDisplay : AbstractMarsToolAndApplication
      */
     override fun reset()
     {
-        resetCounts()
-        updateDisplay()
+        grid.reset()
+        canvas.repaint()
     }
 
-    /**
-     * Updates display immediately after each update (AccessNotice) is processed, after display configuration changes as
-     * needed, and after each execution step when Mars is running in timed mode.  Overrides inherited method that does
-     * nothing.
-     */
-    override fun updateDisplay() = canvas.repaint()
-
     /**
      * Overrides default method, to provide a Help button for this tool/app.
      */
@@ -291,51 +290,55 @@ class BitmapDisplay : AbstractMarsToolAndApplication
     // UI components and layout for left half of GUI, where settings are specified.
     private fun buildOrganizationArea(): JComponent
     {
-        uiUnitWidthSelector = JComboBox(arrayOf(1, 2, 4, 8, 16, 32)).apply {
+        val uiUnitWidthSelector = JComboBox(arrayOf(1, 2, 4, 8, 16, 32)).apply {
             isEditable = false
             background = backgroundColor
             selectedIndex = 1
             toolTipText = "Width in pixels of rectangle representing memory word"
             addActionListener {
+                unitWidth = getInt()
                 grid = createNewGrid()
-                updateDisplay()
+                reset()
             }
         }
 
-        uiUnitHeightSelector = JComboBox(arrayOf(1, 2, 4, 8, 16, 32)).apply {
+        val uiUnitHeightSelector = JComboBox(arrayOf(1, 2, 4, 8, 16, 32)).apply {
             isEditable = false
             background = backgroundColor
             selectedIndex = 1
             toolTipText = "Height in pixels of rectangle representing memory word"
             addActionListener {
+                unitHeight = getInt()
                 grid = createNewGrid()
-                updateDisplay()
+                reset()
             }
         }
 
-        uiWidthSelector = JComboBox(arrayOf(64, 128, 256, 512, 1024)).apply {
+        val uiWidthSelector = JComboBox(arrayOf(64, 128, 256, 512, 1024)).apply {
             isEditable = false
             background = backgroundColor
             selectedIndex = 3
             toolTipText = "Total width in pixels of display area"
             addActionListener {
+                displayWidth = getInt()
                 canvas.preferredSize = displayDimension
                 canvas.size = displayDimension
                 grid = createNewGrid()
-                updateDisplay()
+                reset()
             }
         }
 
-        uiHeightSelector = JComboBox(arrayOf(64, 128, 256, 512, 1024)).apply {
+        val uiHeightSelector = JComboBox(arrayOf(64, 128, 256, 512, 1024)).apply {
             isEditable = false
             background = backgroundColor
             selectedIndex = 2
             toolTipText = "Total height in pixels of display area"
             addActionListener {
+                displayHeight = getInt()
                 canvas.preferredSize = displayDimension
                 canvas.size = displayDimension
                 grid = createNewGrid()
-                updateDisplay()
+                reset()
             }
         }
 
@@ -358,7 +361,7 @@ class BitmapDisplay : AbstractMarsToolAndApplication
                     addAsObserver()
                 }
                 grid = createNewGrid()
-                updateDisplay()
+                reset()
             }
         }
 
@@ -467,9 +470,6 @@ class BitmapDisplay : AbstractMarsToolAndApplication
         return canvas
     }
 
-    // reset all counters in the Grid.
-    private fun resetCounts() = grid.reset()
-
     private fun <T> JComboBox<T>.getInt() = selectedItem!!.toString().toInt()
 
     // Use this for consistent results.
@@ -484,22 +484,6 @@ class BitmapDisplay : AbstractMarsToolAndApplication
         return Grid(rows, columns)
     }
 
-    // Given memory address, update color for the corresponding grid element.
-    private fun updateColorForAddress(notice: MemoryAccessNotice)
-    {
-        val address = notice.address
-        val value = notice.value
-        val offset = (address - baseAddress) / Memory.WORD_LENGTH_BYTES
-        try
-        {
-            grid.setElement(offset / grid.cols, offset % grid.cols, value)
-        }
-        catch (e: IndexOutOfBoundsException)
-        {
-            // If address is out of range for display, do nothing.
-        }
-    }
-
     //////////////////////////////////////////////////////////////////////////////////////
     //  Specialized inner classes for modeling and animation.
     //////////////////////////////////////////////////////////////////////////////////////

src/main/java/mars/tools/InstructionStatistics.java

@@ -318,7 +318,7 @@ public class InstructionStatistics extends AbstractMarsToolAndApplication
             {
 
                 // access the statement in the text segment without notifying other tools etc.
-                ProgramStatement stmt = Memory.getInstance().getStatementNoNotify(memAccNotice.getAddress());
+                ProgramStatement stmt = Memory.getInstance().getStatement(memAccNotice.getAddress());
 
                 // necessary to handle possible null pointers at the end of the program
                 // (e.g., if the simulator tries to execute the next instruction after the last instruction in the text segment)

src/main/java/mars/tools/MipsXray.java

@@ -9,7 +9,6 @@ import mars.mips.hardware.MemoryAccessNotice;
 import mars.mips.instructions.BasicInstruction;
 import mars.mips.instructions.BasicInstructionFormat;
 import mars.venus.RunAssembleAction;
-import mars.venus.RunBackstepAction;
 import mars.venus.RunStepAction;
 import mars.venus.VenusUI;
 import org.w3c.dom.Document;
@@ -313,11 +312,6 @@ public class MipsXray extends AbstractMarsToolAndApplication
                 "Run one step at a time", Integer.valueOf(KeyEvent.VK_T),
                 KeyStroke.getKeyStroke(KeyEvent.VK_F7, 0),
                 mainUI);
-            runBackstepAction = new RunBackstepAction("Backstep",
-                new ImageIcon(tk.getImage(cs.getResource(Globals.imagesPath + "StepBack22.png"))),
-                "Undo the last step", Integer.valueOf(KeyEvent.VK_B),
-                KeyStroke.getKeyStroke(KeyEvent.VK_F8, 0),
-                mainUI);
         }
         catch (Exception e)
         {

src/main/java/mars/venus/RegistersWindow.java

@@ -117,7 +117,7 @@ public class RegistersWindow extends JPanel implements Observer
         }
         tableData[32][0] = "pc";
         tableData[32][1] = "";//new Integer(32);
-        tableData[32][2] = NumberDisplayBaseChooser.formatUnsignedInteger(RegisterFile.getProgramCounter(), valueBase);
+        tableData[32][2] = NumberDisplayBaseChooser.formatUnsignedInteger(RegisterFile.getPc(), valueBase);
 
         tableData[33][0] = "hi";
         tableData[33][1] = "";//new Integer(33);
@@ -184,7 +184,7 @@ public class RegistersWindow extends JPanel implements Observer
         {
             updateRegisterValue(registers[i].getNumber(), registers[i].getValue(), base);
         }
-        updateRegisterUnsignedValue(32, RegisterFile.getProgramCounter(), base);
+        updateRegisterUnsignedValue(32, RegisterFile.getPc(), base);
         updateRegisterValue(33, RegisterFile.getValue(33), base);
         updateRegisterValue(34, RegisterFile.getValue(34), base);
     }
@@ -227,6 +227,7 @@ public class RegistersWindow extends JPanel implements Observer
                 // or stepped mode.
                 if (notice.getRunSpeed() != RunSpeedPanel.UNLIMITED_SPEED || notice.getMaxSteps() == 1)
                 {
+                    System.out.println("Running in timed mode");
                     RegisterFile.addRegistersObserver(this);
                     this.highlighting = true;
                 }

src/main/java/mars/venus/RunBackstepAction.java

@@ -75,12 +75,12 @@ public class RunBackstepAction extends GuiAction
         {
             boolean inDelaySlot = Globals.program.getBackStepper().inDelaySlot(); // Added 25 June 2007
             Memory.getInstance().addObserver(executePane.getDataSegmentWindow());
-            RegisterFile.addRegistersObserver(executePane.getRegistersWindow());
+            //RegisterFile.addRegistersObserver(executePane.getRegistersWindow());
             Coprocessor0.addRegistersObserver(executePane.getCoprocessor0Window());
             Coprocessor1.addRegistersObserver(executePane.getCoprocessor1Window());
             Globals.program.getBackStepper().backStep();
             Memory.getInstance().deleteObserver(executePane.getDataSegmentWindow());
-            RegisterFile.deleteRegistersObserver(executePane.getRegistersWindow());
+            //RegisterFile.deleteRegistersObserver(executePane.getRegistersWindow());
             executePane.getRegistersWindow().updateRegisters();
             executePane.getCoprocessor1Window().updateRegisters();
             executePane.getCoprocessor0Window().updateRegisters();

src/main/java/mars/venus/RunGoAction.java

@@ -170,7 +170,7 @@ public class RunGoAction extends GuiAction
             mainUI.getRegistersPane().setSelectedComponent(executePane.getCoprocessor0Window());
             executePane.getTextSegmentWindow().setCodeHighlighting(true);
             executePane.getTextSegmentWindow().unhighlightAllSteps();
-            executePane.getTextSegmentWindow().highlightStepAtAddress(RegisterFile.getProgramCounter() - 4);
+            executePane.getTextSegmentWindow().highlightStepAtAddress(RegisterFile.getPc() - 4);
         }
         switch (reason)
         {

src/main/java/mars/venus/RunStepAction.java

@@ -126,7 +126,7 @@ public class RunStepAction extends GuiAction
             FileStatus.set(FileStatus.TERMINATED); // should be redundant.
             executePane.getTextSegmentWindow().setCodeHighlighting(true);
             executePane.getTextSegmentWindow().unhighlightAllSteps();
-            executePane.getTextSegmentWindow().highlightStepAtAddress(RegisterFile.getProgramCounter() - 4);
+            executePane.getTextSegmentWindow().highlightStepAtAddress(RegisterFile.getPc() - 4);
         }
         VenusUI.setReset(false);
     }

src/main/java/mars/venus/TextSegmentWindow.java

@@ -577,7 +577,7 @@ public class TextSegmentWindow extends JInternalFrame implements Observer
      */
     public void highlightStepAtPC()
     {
-        highlightStepAtAddress(RegisterFile.getProgramCounter(), false);
+        highlightStepAtAddress(RegisterFile.getPc(), false);
     }
 
     /**
@@ -589,7 +589,7 @@ public class TextSegmentWindow extends JInternalFrame implements Observer
      */
     public void highlightStepAtPC(boolean inDelaySlot)
     {
-        highlightStepAtAddress(RegisterFile.getProgramCounter(), inDelaySlot);
+        highlightStepAtAddress(RegisterFile.getPc(), inDelaySlot);
     }
 
     /**

src/test/java/SpeedTest.kt

@@ -0,0 +1,14 @@
+import mars.Globals
+import mars.mips.hardware.MemoryConfigurations
+import kotlin.system.measureTimeMillis
+
+fun main(args: Array<String>)
+{
+    Globals.initialize(true)
+    MemoryConfigurations.setCurrentConfiguration(MemoryConfigurations.getDefaultConfiguration())
+    println(measureTimeMillis {
+        for (n in 0..100)
+            for (i in 0..128*256)
+                Globals.memory.getWord(0x10008000 + i * 4)
+    })
+}