Apple IIe Emulator (a2e)

A hobby project to create an Apple IIe emulator using my MOS6502 library. Having built a ZX Spectrum emulator in the past, I wanted to tackle the Apple IIe while also getting more experience with modern C++.

Features

CPU & Memory

• 65C02 CPU - Cycle-accurate CMOS 65C02 emulation via the MOS6502 library (1.023 MHz)
• 128KB Memory - Full Apple IIe memory with 64KB main + 64KB auxiliary RAM
• Complete Soft Switches - All IIe memory management (80STORE, RAMRD, RAMWRT, ALTZP, INTCXROM, SLOTC3ROM, etc.)
• Language Card - Full $D000-$FFFF bank switching with two $D000 banks

Display

• Text Modes - 40-column and 80-column text (40x24 / 80x24)
• Graphics Modes - Hi-res (280x192), Lo-res (40x48 with 16 colors), and mixed mode
• Video Standards - NTSC with artifact colors, NTSC with color fringing, PAL color (TCA650) - Experimental, PAL monochrome
• Text Colors - Green phosphor and white text options
• Character ROM - Primary and alternate character sets with flashing character support
• Metal Rendering - Hardware-accelerated display on macOS

Disk II Controller

• Dual Drives - Two disk drives with full stepper motor emulation
• Disk Formats - WOZ 1.0/2.0, DSK, DO (DOS order), PO (ProDOS order)
• Full Read/Write - GCR encoding/decoding with 6-and-2 nibble translation
• Create Disks - Create new blank DOS 3.3 formatted disks from the UI
• Auto-Save - Automatic saving on eject with backup creation

Audio

• Speaker Emulation - 1-bit toggle speaker at $C030
• Audio Output - PortAudio with 48kHz sample rate and ring buffer
• Volume Control - Adjustable volume with mute/unmute
• Audio Sync - Audio-driven timing for cycle-accurate emulation

Input

• Keyboard - Apple IIe keyboard with latch handling, strobe, and key repeat
• Reset - Warm reset (Ctrl+Reset) and hard reset support

Debugger

• Breakpoints - Execution breakpoints with enable/disable
• Watchpoints - Memory read and write watchpoints
• Disassembly - Live disassembly view with PC tracking
• Execution Control - Run, pause, step over, step out
• Memory Visualization - 256x256 pixel map showing memory access patterns (read/write)

Persistent State

• Window positions and sizes saved between sessions
• Emulator state save/load

Building

git submodule update --init --recursive
mkdir build && cd build
cmake ..
cmake --build .
./bin/a2e

Requirements

• CMake 3.20+
• C++20 compiler (Clang 12+, GCC 10+, MSVC 2019+)
• macOS with Metal support
• PortAudio (brew install portaudio)
• Git

ROM Files

Place Apple IIe ROMs in resources/roms/:

resources/roms/
├── 341-0135-A.bin      # CD ROM (4KB)
├── 341-0134-A.bin      # EF ROM (8KB)
├── disk/
│   └── 341-0027.bin    # Disk II controller ROM
└── video/
    └── 341-0160-A.bin  # Character ROM

Usage

Disk Images

The emulator supports multiple disk image formats:

• WOZ 1.0/2.0 - Bit-accurate disk images with variable track lengths
• DSK - Standard 140KB DOS order images
• DO - DOS order images (same as DSK)
• PO - ProDOS order images

Use the Disk Activity window to:

• Load disk images (drag files or use the file browser)
• Create new blank DOS 3.3 formatted disks
• Eject disks (automatically saves any changes with backup)

DOS 3.3 Commands

Once booted into DOS 3.3:

• CATALOG - List files on disk
• INIT HELLO - Format a blank disk with DOS
• SAVE filename - Save current BASIC program
• LOAD filename - Load a BASIC program
• RUN filename - Load and run a program

Keyboard

Standard keys map to Apple IIe equivalents. Control key works for control characters (Ctrl+C, etc.).

Windows

• Video Display - Apple IIe screen with keyboard input capture
• CPU Monitor - Live view of PC, SP, A, X, Y, flags, stack preview, and cycle counter
• Debugger - Disassembly view, breakpoint management, execution controls (step, run, pause)
• Memory Viewer - Full 64KB hex editor with jump-to-address
• Memory Access - 256x256 visualization of memory read/write activity with zoom
• Soft Switches - Current state of all soft switches and video modes
• Disk Activity - Drive status, track position, phase magnets, load/eject/create controls
• Log - Structured logging output with category filtering

Configuration

Settings stored in ~/.config/a2e/:

• preferences.ini - Window visibility
• imgui.ini - Window layout

Current Limitations

• macOS only (Metal rendering)
• No joystick/paddle support
• No double hi-res graphics
• No cassette I/O
• No printer support

Project Structure

a2e/
├── external/           # MOS6502, ImGui, SDL3
├── include/
│   ├── emulator/       # Core emulation (CPU, MMU, Disk II, etc.)
│   └── ui/             # Window classes
├── src/
│   ├── emulator/       # Implementation
│   └── ui/             # UI implementation
└── resources/roms/     # ROM files (not included)

License

TBD