Introducing ROM (+ISX) loader

locale/en-US.txt

@@ -35,6 +35,8 @@ core {
 
 # File dialog
 dialog {
+  ext_isx           ISX modules (*.isx)
+  ext_vb            Virtual Boy ROMs (*.vb)
   load              Load
   load_rom          Load ROM
   load_rom_error    Unable to load the selected ROM file.

src/desktop/app/ROM.java

@@ -0,0 +1,251 @@
+package app;
+
+// Java imports
+import java.nio.charset.*;
+import java.util.*;
+
+// Cartridge ROM module
+public class ROM {
+
+    // Instance fields
+    private byte[] data;   // Binary data
+    private int    format; // File format of loaded file
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    //                               Constants                               //
+    ///////////////////////////////////////////////////////////////////////////
+
+    // Formats
+    public static final int RAW = 0;
+    public static final int ISX = 1;
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    //                                Classes                                //
+    ///////////////////////////////////////////////////////////////////////////
+
+    // ISX code segments
+    private static class Code {
+        int address; // CPU address
+        int offset;  // Position within file
+        int size;    // Number of bytes
+        Code(int o, int a, int s) { address = a; offset =  o; size = s; }
+    }
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    //                             Constructors                              //
+    ///////////////////////////////////////////////////////////////////////////
+
+    // Default constructor
+    ROM(byte[] data) {
+
+        // Attempt to decode as ISX
+        try { isxDecode(data); return; } catch (Exception e) { }
+
+        // Attempt to decode as raw
+        try { rawDecode(data); return; } catch (Exception e) { }
+
+        // Unable to identify the file contents
+        throw new RuntimeException();
+    }
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    //                            Public Methods                             //
+    ///////////////////////////////////////////////////////////////////////////
+
+    // Retrieve the game code from the ROM header
+    public String getGameCode() {
+        var bytes = new byte[4];
+        System.arraycopy(data, data.length - 517, bytes, 0, 4);
+        return new String(bytes, StandardCharsets.ISO_8859_1);
+    }
+
+    // Retrieve the file format of the loaded ROM file
+    public int getFormat() {
+        return format;
+    }
+
+    // Retrieve the maker code from the ROM header
+    public String getMaker() {
+        var bytes = new byte[2];
+        System.arraycopy(data, data.length - 519, bytes, 0, 2);
+        return new String(bytes, StandardCharsets.ISO_8859_1);
+    }
+
+    // Retrieve the number of bytes in the ROM data
+    public int getSize() {
+        return data.length;
+    }
+
+    // Retrieve the game title from the ROM header
+    public String getTitle() {
+        return ShiftJIS.decode(data, data.length - 544, 20).trim();
+    }
+
+    // Retrieve the version number from the ROM header
+    public int getVersion() {
+        return data[data.length - 513] & 0xFF;
+    }
+
+    // Produce a byte array containing the ROM contents
+    public byte[] toByteArray() {
+        return data;
+    }
+
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    //                            Private Methods                            //
+    ///////////////////////////////////////////////////////////////////////////
+
+    // Decode the file data as ISX
+    private void isxDecode(byte[] data) {
+        var codes = isxParse(data); // ISX code segments
+        int head  = -1; // Latest address in bottom half of ROM address space
+        int tail  = -1; // Earliest address in upper half of ROM address space
+
+        // Process all code segments
+        for (var code : codes) {
+            int     end    = code.address + code.size - 1;
+            int     start  = code.address;
+            boolean isHead = end   >= 0; // Lower half of CPU address range
+            boolean isTail = start <  0; // Upper half of CPU address range
+
+            // The segment spans the middle of the ROM address space
+            if (isHead && isTail) {
+                head = 0x7FFFFF;
+                tail = 0x800000;
+                break;
+            }
+
+            // Track the segment's position within the ROM address space
+            end   &= 0x00FFFFFF;
+            start &= 0x00FFFFFF;
+            if (isHead && (head == -1 || head < end  )) head = end;
+            if (isTail && (tail == -1 || tail > start)) tail = start;
+        }
+
+        // Determine the required ROM size
+        int size    = 1024;
+        int minSize = (head == -1 ? 0 : head + 1) +
+            (tail == -1 ? 0 : 0x01000000 - tail);
+        if (minSize == 0 || tail == -1 && (minSize - 1 & minSize) != 0)
+            throw new RuntimeException();
+        for (; size < minSize; size <<= 1);
+
+        // Transfer the code segments into the ROM buffer
+        this.data = new byte[size];
+        for (var code : codes)
+            System.arraycopy(
+                data     , code.offset,
+                this.data, code.address & size - 1,
+                code.size
+            );
+
+        // The ROM is valid
+        format = ISX;
+    }
+
+    // Parse the code records from the ISX data
+    private Code[] isxParse(byte[] data) {
+        int count;
+        int offset = 0;
+        var ret    = new ArrayList<Code>();
+
+        // Check for an extended ISX header
+        if (readInt(data, 0, 3) == 0x585349) // ASCII "ISX"
+            offset = 32;
+
+        // Process records
+        while (offset != data.length)
+        switch (data[offset++] & 0xFF) {
+
+            // SNES code
+            case 0x01:
+                if ((data[offset++] & 0xFF) >= 0x80) // Bank
+                    offset++; // BankHigh
+                offset += 2; // Address
+                offset += 2 + readInt(data, offset, 2); // Data
+                break;
+
+            // SNES range
+            case 0x03:
+                // Count, { Bank, StartAddress, EndAddress, Type }
+                offset += 2 + readInt(data, offset, 2) * 6;
+                break;
+
+            // SNES symbol
+            case 0x04:
+                count = readInt(data, offset, 2); offset += 2;
+                for (; count > 0; count--) // Name, Flags, Bank, Address
+                    offset += 5 + readInt(data, offset, 1);
+                break;
+
+            // Virtual Boy code
+            case 0x11:
+                int address = readInt(data, offset, 4); offset += 4;
+                int size    = readInt(data, offset, 4); offset += 4;
+                if ((address & 0x07000000) != 0x07000000 || size < 0 ||
+                    (address & 0x00FFFFFF) + size > 0x01000000)
+                    throw new RuntimeException();
+                ret.add(new Code(offset, address, size));
+                offset += size;
+                break;
+
+            // Virtual Boy range
+            case 0x13:
+                // Count, { StartAddress, EndAddress, Type }
+                offset += 2 + readInt(data, offset, 2) * 9;
+                break;
+
+            // Virtual Boy symbol
+            case 0x14:
+                count = readInt(data, offset, 2); offset += 2;
+                for (; count > 0; count--) // Name, Flags, Address
+                    offset += 7 + readInt(data, offset, 1);
+                break;
+
+            // System
+            case 0x20: case 0x21: case 0x22:
+                offset += 4 + readInt(data, offset, 4); // Debug, undocumented
+                break;
+
+            // Invalid record type
+            default:
+                throw new RuntimeException();
+        }
+
+        return ret.toArray(new Code[ret.size()]);
+    }
+
+    // Decode the file as raw
+    private void rawDecode(byte[] data) {
+
+        // Validate length
+        if (
+            data.length < 1024       || // Exception handlers and ROM header
+            data.length > 0x00FFFFFF || // 24-bit bus width
+            (data.length & data.length - 1) != 0 // Must be a power of 2
+        ) throw new RuntimeException();
+
+        // The ROM is valid
+        this.data = data;
+        format    = RAW;
+    }
+
+    // Read an integer from a byte array
+    private static int readInt(byte[] data, int offset, int size) {
+        int ret = 0;
+        for (size--; size >= 0; size--)
+            ret = ret << 8 | data[offset + size] & 0xFF;
+        return ret;
+    }
+
+}

src/desktop/app/Window.java

@@ -17,6 +17,7 @@ class Window extends JFrame {
     private App     app;     // Containing application
     private int     number;  // Window number within application
     private boolean only;    // This is the only application window
+    private ROM     rom;     // Currently loaded ROM
     private File    romFile; // Currently loaded ROM file
 
     // UI components
@@ -146,9 +147,9 @@ class Window extends JFrame {
         // Prompt the user to select a file
         var dlgFile = new JFileChooser(pwd);
         dlgFile.addChoosableFileFilter(new FileNameExtensionFilter(
-            "Virtual Boy ROMs (*.vb)", "vb"));
+            loc.get("dialog.ext_vb"), "vb"));
         dlgFile.addChoosableFileFilter(new FileNameExtensionFilter(
-            "ISX modules (*.isx)", "isx"));
+            loc.get("dialog.ext_isx"), "isx"));
         dlgFile.setAcceptAllFileFilterUsed(true);
         dlgFile.setDialogTitle(loc.get("dialog.load_rom"));
         int option = dlgFile.showDialog(this, loc.get("dialog.load"));
@@ -161,7 +162,7 @@ class Window extends JFrame {
         // Update the current directory
         pwd = file.getParentFile();
 
-        // Attempt to load the ROM file
+        // Read the file
         var data = Util.fileRead(file);
         if (data == null) {
             JOptionPane.showMessageDialog(this,
@@ -172,8 +173,21 @@ class Window extends JFrame {
             return;
         }
 
+        // Process the ROM
+        ROM rom = null;
+        try { rom = new ROM(data); }
+        catch (Exception e) {
+            JOptionPane.showMessageDialog(this,
+                loc.get("dialog.load_rom_notvb"),
+                loc.get("dialog.load_rom"),
+                JOptionPane.ERROR_MESSAGE
+            );
+            return;
+        }
+
         // Update the emulation state
-        romFile = file;
+        this.rom = rom;
+        romFile  = file;
         loc.put(this, "ctrl.filename", file.getName());
         updateTitle();
     }