A stripped-down, cross-platform DOS emulator purpose-built for running BBS door games. Derived from dosemu 1.4.0 with sound, graphics, networking, and other subsystems removed - leaving only what door games need.

• C compiler (gcc or clang)
• GNU make
• flex and bison
• slang library (libslang2-dev / slang-devel)

./build.sh

# Linux
./configure && make

# macOS
cp Makefile.conf.darwin Makefile.conf && make

The binary is placed at build/bin/dosdoor.

# Requires: rpm-build, gcc, make, flex, bison, slang-devel
rpmbuild -bb dosdoor.spec

# PhotonBBS-compatible invocation
dosdoor -t -quiet -I "serial { com 1 virtual }" "c:\\doors\\lord.bat 1"

dosdoor -t -quiet

The -I option accepts cpuemu settings:

dosdoor uses a standard dosemu-compatible directory structure:

~/.dosemu/
├── drives/
│   └── c/              Host filesystem mapped as DOS C:\
│       ├── doors/      Door game directories
│       │   ├── lord/   LORD files + NODE*.DAT
│       │   ├── bre/    BRE files + setup configs
│       │   └── ...
│       ├── nodeinfo/   Per-node drop files
│       │   └── 1/
│       │       └── DORINFO1.DEF
│       └── tmp/
└── freedos/            FreeDOS kernel + utilities (bundled)

Each door game needs:

1. Game files in C:\DOORS\<game>\
2. A batch file to launch the game
3. Drop files (DORINFO1.DEF, DOOR.SYS) in a known location

@ECHO OFF
C:
CD \DOORS\LORD
LORD %1 /DREW
EXITEMU

dosdoor works with standard BBS drop file formats:

• DORINFO1.DEF - Most games (Darkness, Simpsons, OOII)
• DOOR.SYS - 52-line format (LORD requires this)
• SRDOOR - BRE uses its own setup utility

dosdoor is a drop-in replacement for dosemu in PhotonBBS doorexec scripts:

# Replace 'dosemu' with 'dosdoor' in existing scripts
dosdoor -t -quiet -I "serial { com 1 virtual }" "c:\\doors\\lord.bat $2"

The DOSEMU_HOGTHRESHOLD environment variable is accepted for backward compatibility (dosdoor has built-in idle detection).

See INTEGRATION.md for detailed migration steps.

dosdoor
├── CPU emulation (src/emu-i386/)
│   ├── simx86 interpreter    All platforms (fullsim)
│   └── simx86 JIT compiler   x86_64 only (full)
├── Serial I/O (src/base/serial/)
│   ├── Virtual COM ports     stdin/stdout mapping
│   ├── UART emulation        16550A register-level
│   ├── INT 14h               BIOS serial services
│   └── FOSSIL driver         TSR-based serial API
├── Terminal (src/plugin/term/)
│   └── ANSI/VT100 output     via slang library
├── Filesystem (src/dosext/mfs/)
│   └── Host dir mapping      C:\ = ~/.dosemu/drives/c/
├── DPMI (src/dosext/dpmi/)
│   └── Protected mode        For doors that need it
├── BIOS (src/base/bios/)
│   ├── INT 10h               Text-mode video
│   ├── INT 16h               Keyboard input
│   └── INT 21h               DOS services
└── Platform (src/arch/)
    ├── linux/                 Signal handling, memory mapping
    └── darwin/                macOS signal handling, mapping

User terminal <-> stdin/stdout <-> virtual COM1 <-> DOS serial API <-> Door game

dosdoor strips everything door games don't need:

• Sound (SB16, MIDI, PC speaker, ALSA, OSS)
• Graphics (VGA, SVGA, VESA, X11, SDL)
• Mouse support
• Networking (IPX, TCP/IP, packet driver)
• SCSI and CDROM
• DMA controller
• Joystick
• GPM mouse integration
• Non-CP437 character sets
• Interactive debugger

GPLv2, inherited from dosemu. See COPYING for the full license text and COPYING.DOSEMU for the original dosemu copyright notice.

dosdoor is built on the work of the dosemu development team. The original dosemu 1.4.0 was released in 2007 and remains one of the most complete DOS emulation implementations for Linux.