Second London Baptist Confession - GBA Reader

A Game Boy Advance homebrew application for reading the Second London Baptist Confession of Faith (1689). This project provides a complete text reader with scrolling, chapter navigation, and a custom font rendering system optimized for the GBA's 240x160 screen.

Features

• Full text display of the 1689 Baptist Confession with all 32 chapters
• Smooth scrolling with proper VSync timing to prevent flicker
• Chapter navigation using A/B buttons to jump between chapters

Controls

Button	Action
UP	Scroll up one line
DOWN	Scroll down one line
A	Jump to next chapter
B	Jump to previous chapter

Quick Start

Option 1: Use Pre-built ROM

Download confession.gba and load it in your favorite GBA emulator.

Option 2: Build from Source

Prerequisites

• devkitPro toolchain with GBA development tools
• Python 3 (for optional JSON conversion)
• GBA emulator (mGBA, VisualBoyAdvance-M, etc.)

Installation Steps

1. Install devkitPro:

   • Windows: Download installer from devkitPro releases
   • Linux: sudo apt install devkitpro-pacman && sudo dkp-pacman -S gba-dev
   • macOS: brew install devkitpro/devkitpro/devkitarm

2. Set environment variables:

   export DEVKITPRO=/opt/devkitpro
   export DEVKITARM=$DEVKITPRO/devkitARM
   export PATH=$DEVKITARM/bin:$PATH

3. Clone and build:

   git clone <repository-url>
   cd gba-confession
   make clean
   make

4. Fix ROM header:

   python3 fix_header.py confession.gba

5. Test in emulator: Load confession.gba in mGBA or your preferred emulator.

Project Structure

gba-confession/
├── confession.c          # Main application code
├── crt0.s               # GBA startup assembly code
├── linker.ld            # Memory layout linker script
├── Makefile             # Build configuration
├── fix_header.py        # ROM header fixer script
├── convert_json.py      # JSON to C array converter
└── README.md            # This file

Customizing Content

The confession text is stored as a C string array in confession.c. To use different text:

Method 1: JSON Conversion (Recommended)

1. Prepare your JSON in the format:

   {
     "title": "Your Document Title",
     "chapters": {
       "1": {
         "title": "Chapter Title",
         "paragraphs": {
           "1": "Paragraph text...",
           "2": "More text..."
         }
       }
     }
   }

2. Convert to GBA format:

   python3 convert_json.py your_document.json

3. Rebuild:

   make clean
   make
   python3 fix_header.py confession.gba

Method 2: Direct Editing

Edit the confession_text[] array in confession.c directly, ensuring:

• Each line is ≤27 characters for proper display
• Update total_lines variable
• Maintain empty strings "" for spacing

Technical Details

Memory Layout

• ROM: Code and data starting at 0x08000000
• IWRAM: Fast work RAM at 0x03000000 (32KB)
• EWRAM: External work RAM at 0x02000000 (256KB)
• VRAM: Video memory at 0x06000000 (in Mode 3)

Graphics System

• Mode 3: 15-bit color, 240x160 resolution
• Direct pixel access to framebuffer
• VSync synchronization to prevent tearing
• Custom font rendering with 8x8 character cells

Text Formatting

• 27 characters per line to accommodate scrollbar
• 12 lines visible on screen simultaneously
• 12-pixel line spacing for readability
• Color coding: Blue for chapter headers, white for text

Troubleshooting

Build Errors

"arm-none-eabi-gcc not found":

• Install devkitPro toolchain
• Check environment variables are set correctly
• Restart terminal after installation

"gbafix not found":

• Install gba-tools: sudo dkp-pacman -S gba-tools
• Or use the Python header fixer: python3 fix_header.py confession.gba

ROM Issues

"Could not load game" in emulator:

• Run header fixer: python3 fix_header.py confession.gba
• Try different emulator (mGBA, VBA-M, No$GBA)
• Check ROM file size (should be several KB, not 0 bytes)

Black screen:

• Verify ROM header is correct with hexdump -C confession.gba | head -5
• Should start with ea 00 00 xx 24 ff ae 51...

Text flickering/overlapping:

• Ensure you're using the latest version with VSync fixes
• Check that wait_vblank() function is being called

Performance

Slow compilation:

• Use make -j4 for parallel compilation
• Consider using Docker if native installation is problematic

Development

Adding Features

The codebase is structured for easy modification:

• Font changes: Edit font_data array in confession.c
• Screen layout: Modify draw_text_screen() function
• Input handling: Update the main game loop
• Colors: Change the color constants at the top of the file

Testing

Test on multiple emulators for compatibility:

• mGBA: Most accurate, recommended for development
• VisualBoyAdvance-M: Good compatibility, cross-platform
• No$GBA: Windows only, good for debugging

For real hardware testing, use flash carts like:

• EZ-Flash Omega DE
• Everdrive GBA X5

Contributing

1. Fork the repository
2. Create a feature branch
3. Test on multiple emulators
4. Ensure ROM works on real hardware (if possible)
5. Submit a pull request

License

This project is released into the public domain. The Second London Baptist Confession of Faith (1689) is a historical document in the public domain.

References

• Second London Baptist Confession (1689)
• GBA Development Resources
• devkitPro Documentation
• Tonc GBA Programming Tutorial

Acknowledgments

• devkitPro team for the excellent GBA toolchain
• Baptist churches for preserving this historic confession
• GBA homebrew community for documentation and tools

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For support or questions, please open an issue on the project repository.