Revisions to CPU register interface

locale/en-US.txt

@@ -41,7 +41,8 @@ console {
 cpu {
   float         Float
   hex           Hex
-  last_pc   Last PC
+  jump_from     From
+  jump_to       To
   signed        Signed
   title         CPU
   unsigned      Unsigned

src/core/bus.c

@@ -62,9 +62,9 @@ static int32_t busReadValue(VUE *vue, uint32_t address, int type) {
         case 5: /* System WRAM */
             return busReadMemory(vue->bus.wram, address & 0xFFFF, type);
         case 6: return busReadMemory(vue->bus.sram, /* Cartridge RAM */
-            address & (vue->bus.sram_size - 1), type);
+            address & (vue->bus.sramSize - 1), type);
         case 7: return busReadMemory(vue->bus.rom , /* Cartridge ROM */
-            address & (vue->bus.rom_size  - 1), type);
+            address & (vue->bus.romSize  - 1), type);
     }
     return 0; /* Unreachable */
 }
@@ -128,11 +128,11 @@ static void busWriteValue(VUE *vue, uint32_t address, int type, int32_t value){
             break;
         case 6: /* Cartridge RAM */
             busWriteMemory(vue->bus.sram,
-                address & (vue->bus.sram_size - 1), type, value);
+                address & (vue->bus.sramSize - 1), type, value);
             break;
         case 7: /* Cartridge ROM */
             busWriteMemory(vue->bus.rom ,
-                address & (vue->bus.rom_size  - 1), type, value);
+                address & (vue->bus.romSize  - 1), type, value);
             break;
     }
 }

src/core/cpu.c

@@ -142,7 +142,8 @@ static void cpuReset(VUE *vue) {
 
     /* Configure registers */
     vue->cpu.ecr_eicc = 0xFFF0;
-    vue->cpu.lastPC   = 0xFFFFFFF0;
+    vue->cpu.jumpFrom = 0xFFFFFFF0;
+    vue->cpu.jumpTo   = 0xFFFFFFF0;
     vue->cpu.pc       = 0xFFFFFFF0;
     vue->cpu.psw_np   = 1;
 }

src/core/include/vue.h

@@ -38,11 +38,15 @@ extern "C" {
 #define VUE_EIPSW  1
 #define VUE_FEPC   2
 #define VUE_FEPSW  3
-#define VUE_PC    -1
 #define VUE_PIR    6
 #define VUE_PSW    5
 #define VUE_TKCW   7
 
+/* Non-standard register indexes */
+#define VUE_PC        -1
+#define VUE_JUMP_FROM -2
+#define VUE_JUMP_TO   -3
+
 /* Program register indexes */
 #define VUE_GP  4
 #define VUE_HP  2
@@ -65,9 +69,9 @@ typedef struct {
     /* Memory bus */
     struct {
         uint8_t *rom;           /* Cartridge ROM */
-        uint32_t rom_size;      /* Number of bytes in cartridge ROM */
+        uint32_t romSize;       /* Number of bytes in cartridge ROM */
         uint8_t *sram;          /* Cartridge RAM */
-        uint32_t sram_size;     /* Number of bytes in cartridge RAM */
+        uint32_t sramSize;      /* Number of bytes in cartridge RAM */
         uint8_t  wram[0x10000]; /* System memory */
     } bus;
 
@@ -75,7 +79,8 @@ typedef struct {
     struct {
         uint32_t cycles;   /* Cycles until next stage */
         int      fetch;    /* Fetch unit index */
-        int32_t  lastPC; /* Previous value of PC */
+        int32_t  jumpFrom; /* Source PC of most recent jump */
+        int32_t  jumpTo;   /* Destination PC of most recent jump */
         int      stage;    /* Current processing stage */
 
         /* Program registers */

src/core/vue.c

@@ -26,8 +26,20 @@ static const int TYPE_SIZES[] = { 1, 1, 2, 2, 4 };
 
 /* Retrieve the value of a register */
 int32_t vueGetRegister(VUE *vue, int index, vbool system) {
-    return vue == NULL ? 0 :
+
-        index == VUE_PC && system ? vue->cpu.pc :
+    /* Error checking */
+    if (vue == NULL)
+        return 0;
+
+    /* Non-indexed registers */
+    if (system) switch (index) {
+        case VUE_PC       : return vue->cpu.pc;
+        case VUE_JUMP_FROM: return vue->cpu.jumpFrom;
+        case VUE_JUMP_TO  : return vue->cpu.jumpTo;
+    }
+
+    /* Indexed registers */
+    return
         index < 0 || index > 31 ? 0 :
         system ? cpuGetSystemRegister(vue, index) :
         vue->cpu.program[index]
@@ -69,10 +81,10 @@ vbool vueRead(VUE *vue, uint32_t address, uint8_t *dest, uint32_t length) {
                 address, 0x10000          , count);
                 break;
             case 6: busReadBytes(vue->bus.sram, dest, /* Cartridge RAM */
-                address, vue->bus.sram_size, count);
+                address, vue->bus.sramSize, count);
                 break;
             case 7: busReadBytes(vue->bus.rom , dest, /* Cartridge ROM */
-                address, vue->bus.rom_size , count);
+                address, vue->bus.romSize , count);
                 break;
         }
 
@@ -111,7 +123,7 @@ vbool vueSetROM(VUE *vue, uint8_t *rom, uint32_t size) {
 
     /* Accept the new ROM buffer */
     vue->bus.rom     = rom;
-    vue->bus.rom_size = size;
+    vue->bus.romSize = size;
     return VUE_TRUE;
 }
 
@@ -137,10 +149,10 @@ vbool vueWrite(VUE *vue, uint32_t address, uint8_t *src, uint32_t length) {
                 busWriteBytes(vue->bus.wram, src, address, 0x10000, count);
                 break;
             case 6: busWriteBytes(vue->bus.sram, src, /* Cartridge RAM */
-                address, vue->bus.sram_size, count);
+                address, vue->bus.sramSize, count);
                 break;
             case 7: busWriteBytes(vue->bus.rom , src, /* Cartridge ROM */
-                address, vue->bus.rom_size , count);
+                address, vue->bus.romSize , count);
                 break;
         }
 

src/desktop/app/App.java

@@ -11,11 +11,13 @@ import vue.*;
 public class App {
 
     // Instance fields
-    private Localizer localizer; // UI localization manager
     private boolean   useNative; // Produce native core contexts
     private Localizer.Locale[]    locales; // Language translations
     private ArrayList<MainWindow> windows; // Application windows
 
+    // Configuration fields
+    Localizer localizer; // UI localization manager
+
 
 
     ///////////////////////////////////////////////////////////////////////////
@@ -47,21 +49,11 @@ public class App {
         windowsChanged();
     }
 
-    // Retrieve the currently active locale
-    Localizer.Locale getLocale() {
-        return localizer.getLocale();
-    }
-
     // Determine whether the native module is in use
     boolean getUseNative() {
         return useNative;
     }
 
-    // Retrieve the localization manager
-    Localizer getLocalizer() {
-        return localizer;
-    }
-
     // Retrieve a list of registered locales
     Localizer.Locale[] listLocales() {
         var ret = new Localizer.Locale[locales.length];
@@ -80,11 +72,6 @@ public class App {
         windowsChanged();
     }
 
-    // Specify a new locale
-    void setLocale(Localizer.Locale locale) {
-        localizer.setLocale(locale);
-    }
-
     // Specify whether using the native module
     boolean setUseNative(boolean useNative) {
         return this.useNative = useNative && VUE.isNativeLoaded();

src/desktop/app/CPU.java

@@ -56,7 +56,7 @@ class CPU extends ChildWindow {
         outer.setResizeWeight(1);
 
         client.add(outer);
-        client.setPreferredSize(new Dimension(640, 480));
+        client.setPreferredSize(new Dimension(480, 300));
         setFont2(font);
         pack();
     }
@@ -102,7 +102,8 @@ class CPU extends ChildWindow {
                 case VUE.SP: name = "sp"; break;
                 case VUE.TP: name = "tp"; break;
             }
-            registers.add(new Register(parent,lst,name,x,Register.PROGRAM));
+            registers.add(new Register(
+                parent, lst, name, x, Register.PROGRAM));
         }
         endList(lst);
     }
@@ -142,7 +143,8 @@ class CPU extends ChildWindow {
         system.putClientProperty("shown", true);
 
         // Add the first two system registers and expand PSW
-        registers.add(new Register(parent, lst, "PC"   , VUE.PC   , VUE.PC  ));
+        int plain = Register.PLAIN;
+        registers.add(new Register(parent, lst, "PC"   , VUE.PC   , plain   ));
         Register psw =new Register(parent, lst, "PSW"  , VUE.PSW  , VUE.PSW );
         psw.setExpanded(true);
         registers.add(psw);
@@ -151,18 +153,18 @@ class CPU extends ChildWindow {
         shown = false;
 
         // Add the remaining system registers
-        registers.add(new Register(parent, lst, "EIPC" , VUE.EIPC , VUE.PC  ));
+        registers.add(new Register(parent, lst, "EIPC" , VUE.EIPC , plain   ));
         registers.add(new Register(parent, lst, "EIPSW", VUE.EIPSW, VUE.PSW ));
-        registers.add(new Register(parent, lst, "FEPC" , VUE.FEPC , VUE.PC  ));
+        registers.add(new Register(parent, lst, "FEPC" , VUE.FEPC , plain   ));
         registers.add(new Register(parent, lst, "FEPSW", VUE.FEPSW, VUE.PSW ));
         registers.add(new Register(parent, lst, "ECR"  , VUE.ECR  , VUE.ECR ));
-        registers.add(new Register(parent, lst, "ADTRE", VUE.ADTRE, VUE.PC  ));
+        registers.add(new Register(parent, lst, "ADTRE", VUE.ADTRE, plain   ));
         registers.add(new Register(parent, lst, "CHCW" , VUE.CHCW , VUE.CHCW));
         registers.add(new Register(parent, lst, "PIR"  , VUE.PIR  , VUE.PIR ));
         registers.add(new Register(parent, lst, "TKCW" , VUE.TKCW , VUE.TKCW));
-        registers.add(new Register(parent, lst, "29"   ,        29, VUE.PC  ));
+        registers.add(new Register(parent, lst, "29"   ,        29, plain   ));
-        registers.add(new Register(parent, lst, "30"   ,        30, VUE.PC  ));
+        registers.add(new Register(parent, lst, "30"   ,        30, plain   ));
-        registers.add(new Register(parent, lst, "31"   ,        31, VUE.PC  ));
+        registers.add(new Register(parent, lst, "31"   ,        31, plain   ));
         endList(lst);
     }
 

src/desktop/app/ChildWindow.java

@@ -27,7 +27,7 @@ class ChildWindow extends JInternalFrame {
         this.parent = parent;
 
         // Configure component
-        parent.app.getLocalizer().add(this, key);
+        parent.app.localizer.add(this, key);
         addInternalFrameListener(Util.onClose2(e->setVisible(false)));
         setClosable(true);
         setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);

src/desktop/app/MainWindow.java

@@ -87,7 +87,7 @@ class MainWindow extends JFrame {
         setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
         setIconImage(APPICON);
         setJMenuBar(initMenus());
-        app.getLocalizer().add(this, "app.title.default");
+        app.localizer.add(this, "app.title.default");
 
         // Configure child windows
         desktop = new JDesktopPane();
@@ -112,7 +112,7 @@ class MainWindow extends JFrame {
     // Produce the window's menu bar
     private JMenuBar initMenus() {
         var bar = new JMenuBar();
-        var loc = app.getLocalizer();
+        var loc = app.localizer;
         bar.add(initMenuFile (loc));
         bar.add(initMenuDebug(loc));
         return bar;
@@ -194,7 +194,7 @@ class MainWindow extends JFrame {
     void windowsChanged(int number, boolean only) {
         this.number = number;
         this.only   = only;
-        app.getLocalizer().put(this, "ctrl.number", "" + number);
+        app.localizer.put(this, "ctrl.number", "" + number);
         updateTitle();
     }
 
@@ -239,7 +239,7 @@ class MainWindow extends JFrame {
 
     // File -> Load ROM
     private void onLoadROM() {
-        var loc = app.getLocalizer();
+        var loc = app.localizer;
 
         // Prompt the user to select a file
         var dlgFile = new JFileChooser(pwd);
@@ -324,7 +324,7 @@ class MainWindow extends JFrame {
 
     // Update the window title
     private void updateTitle() {
-        app.getLocalizer().add(this,
+        app.localizer.add(this,
             only ? romFile != null ?
                 "app.title.rom" :
                 "app.title.default"

src/desktop/app/Memory.java

@@ -57,7 +57,7 @@ class Memory extends ChildWindow {
         client.addMouseWheelListener(e->onWheel(e));
         client.setBackground(SystemColor.window);
         client.setFocusable(true);
-        client.setPreferredSize(new Dimension(640, 480));
+        client.setPreferredSize(new Dimension(480, 360));
 
         // Configure component
         var content = new JPanel(new BorderLayout());

src/desktop/app/Register.java

@@ -14,6 +14,7 @@ import vue.*;
 class Register {
 
     // Instance fields
+    boolean    expandable; // The expansion area can be shown
     boolean    expanded;   // The expanded area is being shown
     Font       font;       // Hexadecimal font
     int        index;      // Register index
@@ -25,9 +26,12 @@ class Register {
     // UI components
     private JPanel     expansion;   // Expansion area
     private JLabel     btnExpand;   // Expand button
+    private JLabel     lblLastPC;   // Last PC name
     private JLabel     lblName;     // Register name
     private JPanel     list;        // Containing element
     private JPanel     spacer;      // Expansion area spacer
+    private JTextField txtJumpFrom; // Jump-from value
+    private JTextField txtJumpTo;   // Jump-to value
     private JTextField txtValue;    // Register value
     private ArrayList<JComponent> controls; // Expansion controls
 
@@ -44,6 +48,7 @@ class Register {
     static final int UNSIGNED = 2;
 
     // Types
+    static final int PLAIN   = -1;
     static final int PROGRAM = -2;
 
 
@@ -57,6 +62,7 @@ class Register {
 
         // Configure instance fields
         controls    = new ArrayList<JComponent>();
+        expandable  = type != PLAIN && index != 0 || index == VUE.PC;
         this.index  = index;
         this.list   = list;
         this.mode   = HEX;
@@ -64,13 +70,13 @@ class Register {
         this.type   = type;
 
         // Click handler for expand and name controls
-        MouseListener expand = type == VUE.PC ? null : Util.onMouse(
+        MouseListener expand = !expandable ? null : Util.onMouse(e->{
-            e->{ if (e.getButton() == 1) setExpanded(!expanded); }, null);
+                if (e.getButton() == 1) setExpanded(!expanded); }, null);
 
         // Expand button
-        btnExpand = new JLabel(expand != null ? "+" : " ");
+        btnExpand = new JLabel(expandable ? "+" : " ");
         btnExpand.setHorizontalAlignment(SwingConstants.CENTER);
-        if (expand != null)
+        if (expandable)
             btnExpand.addMouseListener(expand);
         var gbc = new GridBagConstraints();
         gbc.anchor = GridBagConstraints.NORTH;
@@ -79,7 +85,7 @@ class Register {
 
         // Name label
         lblName = new JLabel(name);
-        if (expand != null)
+        if (expandable)
             lblName.addMouseListener(expand);
         gbc = new GridBagConstraints();
         gbc.anchor  = GridBagConstraints.NORTH;
@@ -116,6 +122,7 @@ class Register {
             case PROGRAM : initProgram(); break;
             case VUE.CHCW: initCHCW   (); break;
             case VUE.ECR : initECR    (); break;
+            case VUE.PC  : initPC     (); break;
             case VUE.PIR : initPIR    (); break;
             case VUE.PSW : initPSW    (); break;
             case VUE.TKCW: initTKCW   (); break;
@@ -123,19 +130,25 @@ class Register {
         }
 
         // Expansion spacer
+        if (index != VUE.PC) {
             spacer = new JPanel(null);
             spacer.setOpaque(false);
             spacer.setPreferredSize(new Dimension(0, 0));
             spacer.setVisible(false);
-        list.add(spacer, new GridBagConstraints());
+            gbc = new GridBagConstraints();
+            list.add(spacer, gbc);
+        }
 
         // Expansion area
         expansion.setOpaque(false);
         expansion.setVisible(false);
         gbc = new GridBagConstraints();
         gbc.anchor    = GridBagConstraints.WEST;
+        if (index == VUE.PC)
+            gbc.fill  = GridBagConstraints.HORIZONTAL;
         gbc.gridwidth = GridBagConstraints.REMAINDER;
         gbc.insets    = new Insets(0, 4, 0, 0);
+        gbc.weightx   = 1;
         list.add(expansion, gbc);
     }
 
@@ -168,6 +181,50 @@ class Register {
         group.add(addRadioButton("cpu.float"   , FLOAT   ));
     }
 
+    // Expansion controls for PC
+    private void initPC() {
+        expansion = new JPanel(new GridBagLayout());
+
+        // Configure controls
+        for (int x = 0; x < 2; x++) {
+
+            // Indentation
+            var spacer = new JPanel(null);
+            spacer.setOpaque(false);
+            spacer.setPreferredSize(new Dimension(0, 0));
+            var gbc = new GridBagConstraints();
+            gbc.weightx = 1;
+            expansion.add(spacer, gbc);
+        
+            // Name label
+            var label = new JLabel();
+            parent.app.localizer.add(label,
+                x == 0 ? "cpu.jump_from" : "cpu.jump_to" );
+            gbc = new GridBagConstraints();
+            gbc.anchor = GridBagConstraints.NORTHWEST;
+            expansion.add(label, gbc);
+        
+            // Value text box
+            var txt = new JTextField();
+            txt.addActionListener(e->{
+                txt.setText((String) txt.getClientProperty("text"));
+                list.requestFocus();
+            });
+            txt.setBorder(null);
+            txt.setOpaque(false);
+            gbc = new GridBagConstraints();
+            gbc.gridwidth = GridBagConstraints.REMAINDER;
+            gbc.insets    = new Insets(0, 4, 0, 0);
+            expansion.add(txt, gbc);
+        
+            // Initialize the corresponding component field
+            if (x == 0)
+                txtJumpFrom = txt;
+            else txtJumpTo = txt;
+        }
+
+    }
+
     // Expansion controls for PSW
     private void initPSW() {
         expansion = new JPanel(new GridBagLayout());
@@ -226,8 +283,18 @@ class Register {
             Float.toString(Float.intBitsToFloat(value))
         );
 
-        // Expansion controls
+        // PC expansion controls
-        for (var control : controls) {
+        if (index == VUE.PC) for (int x = 0; x < 2; x++) {
+            JTextField txt = x == 0 ? txtJumpFrom : txtJumpTo;
+            int index = x == 0 ? VUE.JUMP_FROM : VUE.JUMP_TO;
+            int value = parent.vue.getRegister(index, true);
+            String text = String.format("%08X", value);
+            txt.putClientProperty("text", text);
+            txt.setText(text);
+        }
+
+        // Other expansion controls
+        else for (var control : controls) {
 
             // Check box
             if (control instanceof JCheckBox) {
@@ -256,16 +323,16 @@ class Register {
     void setExpanded(boolean expanded) {
 
         // Error checking
-        if (type == VUE.PC)
+        if (!expandable)
             return;
 
         // Update controls
         this.expanded = expanded;
-        btnExpand.setText   (expanded ? "-" : "+");
+        btnExpand.setText(expanded ? "-" : "+");
+        if (index != VUE.PC)
+            spacer.setVisible(expanded);
         expansion.setVisible(expanded);
-        spacer   .setVisible(expanded);
         list.revalidate();
-        list.repaint();
     }
 
     // Specify the width of the expand button
@@ -280,9 +347,15 @@ class Register {
         this.font = font;
 
         // Value text box
+        var size = new Dimension(8 * fontWidth + 4, fontHeight);
         txtValue.setFont(font);
-        txtValue.setPreferredSize(
+        txtValue.setPreferredSize(size);
-            new Dimension(8 * fontWidth + 4, fontHeight));
+        if (index == VUE.PC) {
+            txtJumpFrom.setFont(font);
+            txtJumpFrom.setPreferredSize(size);
+            txtJumpTo  .setFont(font);
+            txtJumpTo  .setPreferredSize(size);
+        }
 
         // Expansion controls
         for (var ctrl : controls) {
@@ -291,7 +364,7 @@ class Register {
             if ((Boolean) ctrl.getClientProperty("hex"))
                 ((JTextField) ctrl).setFont(font);
             int digits = (Integer) ctrl.getClientProperty("digits");
-            var size   = ctrl.getPreferredSize();
+            size       = ctrl.getPreferredSize();
             size.width = digits * fontWidth + 4;
             ctrl.setPreferredSize(size);
         }
@@ -334,7 +407,7 @@ class Register {
         var gbc = new GridBagConstraints();
         gbc.anchor    = GridBagConstraints.NORTHWEST;
         gbc.gridwidth = 2;
-        gbc.insets    = new Insets(0, 4, 0, 0);
+        gbc.insets    = new Insets(0, 4, 0, 4);
         expansion.add(ctrl, gbc);
     }
 
@@ -343,7 +416,7 @@ class Register {
 
         // Configure control
         var ctrl = new JRadioButton();
-        parent.app.getLocalizer().add(ctrl, key);
+        parent.app.localizer.add(ctrl, key);
         ctrl.setBorder(null);
         ctrl.setFocusable(false);
         ctrl.setOpaque(false);

src/desktop/util/Localizer.java

@@ -314,6 +314,7 @@ public class Localizer {
                 control instanceof AbstractButton ||
                 control instanceof JFrame         ||
                 control instanceof JInternalFrame ||
+                control instanceof JLabel         ||
                 control instanceof JPanel         || // TitledBorder
                 control instanceof JTextComponent
             )) return false;
@@ -490,6 +491,8 @@ public class Localizer {
             ((JFrame        ) control).setTitle(values[0]);
         if (control instanceof JInternalFrame)
             ((JInternalFrame) control).setTitle(values[0]);
+        if (control instanceof JLabel        )
+            ((JLabel        ) control).setText (values[0]);
         if (control instanceof JTextComponent)
             ((JTextComponent) control).setText (values[0]);
 

src/desktop/vue/CPU.java

@@ -9,7 +9,8 @@ class CPU {
     // Package fields
     int cycles;   // Cycles until next stage
     int fetch;    // Fetch unit index
-    int lastPC; // Previous value of PC
+    int jumpFrom; // Source PC of most recent jump
+    int jumpTo;   // Destination PC of most recent jump
     int stage;    // Current processing stage
 
     // Program registers
@@ -149,7 +150,8 @@ class CPU {
 
         // Configure registers
         ecr_eicc = 0xFFF0;
-        lastPC   = 0xFFFFFFF0;
+        jumpFrom = 0xFFFFFFF0;
+        jumpTo   = 0xFFFFFFF0;
         pc       = 0xFFFFFFF0;
         psw_np   = 1;
     }

src/desktop/vue/JavaVUE.java

@@ -40,8 +40,16 @@ class JavaVUE extends VUE {
 
     // Retrieve a register value
     public int getRegister(int index, boolean system) {
+
+        // Non-indexed registers
+        if (system) switch (index) {
+            case VUE.PC       : return cpu.pc;
+            case VUE.JUMP_FROM: return cpu.jumpFrom;
+            case VUE.JUMP_TO  : return cpu.jumpTo;
+        }
+
+        // Indexed registers
         return
-            index == VUE.PC && system ? cpu.pc :
             index < 0 || index > 31 ? 0 :
             system ? cpu.getSystemRegister(index) :
             cpu.program[index]

src/desktop/vue/NativeVUE.c

@@ -99,9 +99,9 @@ JNIEXPORT jbyteArray JNICALL Java_vue_NativeVUE_getROM
         return NULL;
 
     // Copy the ROM data
-    jbyteArray ret   = (*env)->NewByteArray(env, (jint)core->vue.bus.rom_size);
+    jbyteArray ret   = (*env)->NewByteArray(env, (jint)core->vue.bus.romSize);
     jbyte     *elems = (*env)->GetByteArrayElements(env, ret, NULL);
-    memcpy(elems, core->vue.bus.rom, core->vue.bus.rom_size);
+    memcpy(elems, core->vue.bus.rom, core->vue.bus.romSize);
     (*env)->ReleaseByteArrayElements(env, ret, elems, 0);
     return ret;
 }

src/desktop/vue/VUE.java

@@ -27,11 +27,15 @@ public abstract class VUE {
     public static final int EIPSW   =  1;
     public static final int FEPC    =  2;
     public static final int FEPSW   =  3;
-    public static final int PC    = -1;
     public static final int PIR     =  6;
     public static final int PSW     =  5;
     public static final int TKCW    =  7;
 
+    // Non-standard register indexes
+    public static final int PC        = -1;
+    public static final int JUMP_FROM = -2;
+    public static final int JUMP_TO   = -3;
+
     // Program register indexes
     public static final int GP =  4;
     public static final int HP =  2;