DVX — DOS Visual eXecutive

A Windows 3.x-style desktop shell for DOS, built with DJGPP/DPMI. Combines a windowed GUI compositor, cooperative task switcher, and DXE3 dynamic loading to create a multitasking desktop environment where applications are .app shared libraries loaded at runtime.

Components

dvxgui/
  dvx/          GUI compositor library          -> lib/libdvx.a
  tasks/        Cooperative task switcher        -> lib/libtasks.a
  dvxshell/     Desktop shell                    -> bin/dvx.exe
  apps/         DXE app modules (.app files)     -> bin/apps/*/*.app
  rs232/        ISR-driven UART serial driver     -> lib/librs232.a
  packet/       HDLC framing, CRC, Go-Back-N     -> lib/libpacket.a
  security/     DH key exchange, XTEA-CTR cipher  -> lib/libsecurity.a
  seclink/      Secure serial link wrapper        -> lib/libseclink.a
  proxy/        Linux SecLink-to-telnet proxy     -> bin/secproxy
  termdemo/     Encrypted ANSI terminal demo      -> bin/termdemo.exe

Building

Requires the DJGPP cross-compiler (i586-pc-msdosdjgpp-gcc).

make -C dvx         # builds lib/libdvx.a
make -C tasks       # builds lib/libtasks.a
make -C dvxshell    # builds bin/dvx.exe
make -C apps        # builds bin/apps/*/*.app

Set DJGPP_PREFIX in the Makefiles if your toolchain is installed somewhere other than ~/djgpp/djgpp.

Architecture

The shell runs as a single DOS executable (dvx.exe) that loads applications dynamically via DJGPP's DXE3 shared library system. Each app is a .app file exporting an appDescriptor and appMain entry point.

+-------------------------------------------------------------------+
|                        dvx.exe (Task 0)                       |
|  +-------------+  +-----------+  +----------+  +----------------+ |
|  +-------------+  +-----------+  +------------+                  |
|  | shellMain   |  | shellApp  |  | shellExport|                  |
|  | (event loop)|  | (lifecycle|  | (DXE symbol|                  |
|  |             |  |  + reaper)|  |  export)   |                  |
|  +-------------+  +-----------+  +------------+                  |
|         |               |              |                           |
|  +------+-------+  +----+-----+  +----+----+                      |
|  | libdvx.a     |  |libtasks.a|  | libdxe  |                      |
|  | (GUI/widgets)|  |(scheduler)|  | (DJGPP) |                      |
|  +--------------+  +----------+  +---------+                      |
+-------------------------------------------------------------------+
         |                    |
    +---------+          +---------+
    | app.app |          | app.app |
    | (Task N)|          | (Task M)|
    +---------+          +---------+

App Types

Callback-only (hasMainLoop = false): appMain creates windows, registers callbacks, and returns. The app lives through event callbacks in the shell's main loop. No dedicated task or stack needed.

Main-loop (hasMainLoop = true): A cooperative task is created for the app. appMain runs its own loop calling tsYield() to share CPU. Used for apps that need continuous processing (clocks, terminal emulators, games).

Crash Recovery

The shell installs signal handlers for SIGSEGV, SIGFPE, and SIGILL. If an app crashes, the handler longjmps back to the shell's main loop, the crashed app is force-killed, and the shell continues running. Diagnostic information (registers, faulting EIP) is logged to dvx.log.

Sample Apps

App	Type	Description
progman.app	Callback	Program Manager: app launcher grid, Task Manager
notepad.app	Callback	Text editor with file I/O
clock.app	Main-loop	Digital clock (multi-instance capable)
dvxdemo.app	Callback	Widget system showcase

Target Platform

• CPU: 486 baseline, Pentium-optimized paths where significant
• Video: VESA VBE 2.0+ with linear framebuffer
• OS: DOS with DPMI (CWSDPMI or equivalent)
• Test platform: 86Box

Deployment

mcopy -o -i <floppy.img> bin/dvx.exe ::DVX.EXE
mcopy -s -o -i <floppy.img> bin/apps ::APPS

The apps/ directory structure must be preserved on the target — Program Manager recursively scans apps/ for .app files at startup.

Documentation

Each component directory has its own README with detailed API reference:

• dvx/README.md — GUI library architecture and API
• tasks/README.md — Task switcher API
• dvxshell/README.md — Shell internals and DXE app contract
• apps/README.md — Writing DXE applications
• rs232/README.md — Serial port driver
• packet/README.md — Packet transport protocol
• security/README.md — Cryptographic primitives
• seclink/README.md — Secure serial link
• proxy/README.md — Linux SecLink proxy
• termdemo/README.md — Encrypted terminal demo