122 lines
5 KiB
Markdown
122 lines
5 KiB
Markdown
# DVX -- DOS Visual eXecutive
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A Windows 3.x-style desktop shell for DOS, built with DJGPP/DPMI. Combines a
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windowed GUI compositor, cooperative task switcher, and DXE3 dynamic loading to
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create a multitasking desktop environment where applications are `.app` shared
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libraries loaded at runtime.
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## Components
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```
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dvxgui/
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dvx/ GUI compositor library -> lib/libdvx.a
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tasks/ Cooperative task switcher -> lib/libtasks.a
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dvxshell/ Desktop shell -> bin/dvx.exe
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apps/ DXE app modules (.app files) -> bin/apps/*/*.app
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rs232/ ISR-driven UART serial driver -> lib/librs232.a
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packet/ HDLC framing, CRC, Go-Back-N -> lib/libpacket.a
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security/ DH key exchange, XTEA-CTR cipher -> lib/libsecurity.a
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seclink/ Secure serial link wrapper -> lib/libseclink.a
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proxy/ Linux SecLink-to-telnet proxy -> bin/secproxy
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termdemo/ Encrypted ANSI terminal demo -> bin/termdemo.exe
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```
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## Building
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Requires the DJGPP cross-compiler (`i586-pc-msdosdjgpp-gcc`).
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```
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make -C dvx # builds lib/libdvx.a
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make -C tasks # builds lib/libtasks.a
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make -C dvxshell # builds bin/dvx.exe
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make -C apps # builds bin/apps/*/*.app
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```
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Set `DJGPP_PREFIX` in the Makefiles if your toolchain is installed somewhere
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other than `~/djgpp/djgpp`.
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## Architecture
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The shell runs as a single DOS executable (`dvx.exe`) that loads
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applications dynamically via DJGPP's DXE3 shared library system. Each app
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is a `.app` file exporting an `appDescriptor` and `appMain` entry point.
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```
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+-------------------------------------------------------------------+
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| dvx.exe (Task 0) |
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| +-------------+ +-----------+ +----------+ +----------------+ |
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| +-------------+ +-----------+ +------------+ |
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| | shellMain | | shellApp | | shellExport| |
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| | (event loop)| | (lifecycle| | (DXE symbol| |
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| | | | + reaper)| | export) | |
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| +-------------+ +-----------+ +------------+ |
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| | | | |
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| +------+-------+ +----+-----+ +----+----+ |
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| | libdvx.a | |libtasks.a| | libdxe | |
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| | (GUI/widgets)| |(scheduler)| | (DJGPP) | |
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| +--------------+ +----------+ +---------+ |
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+-------------------------------------------------------------------+
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+---------+ +---------+
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| app.app | | app.app |
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| (Task N)| | (Task M)|
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+---------+ +---------+
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```
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### App Types
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**Callback-only** (`hasMainLoop = false`): `appMain` creates windows, registers
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callbacks, and returns. The app lives through event callbacks in the shell's
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main loop. No dedicated task or stack needed.
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**Main-loop** (`hasMainLoop = true`): A cooperative task is created for the app.
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`appMain` runs its own loop calling `tsYield()` to share CPU. Used for apps that
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need continuous processing (clocks, terminal emulators, games).
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### Crash Recovery
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The shell installs signal handlers for SIGSEGV, SIGFPE, and SIGILL. If an app
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crashes, the handler `longjmp`s back to the shell's main loop, the crashed app
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is force-killed, and the shell continues running. Diagnostic information
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(registers, faulting EIP) is logged to `dvx.log`.
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## Sample Apps
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| App | Type | Description |
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|-----|------|-------------|
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| `progman.app` | Callback | Program Manager: app launcher grid, Task Manager |
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| `notepad.app` | Callback | Text editor with file I/O |
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| `clock.app` | Main-loop | Digital clock (multi-instance capable) |
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| `dvxdemo.app` | Callback | Widget system showcase |
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## Target Platform
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- **CPU**: 486 baseline, Pentium-optimized paths where significant
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- **Video**: VESA VBE 2.0+ with linear framebuffer
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- **OS**: DOS with DPMI (CWSDPMI or equivalent)
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- **Test platform**: 86Box
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## Deployment
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```
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mcopy -o -i <floppy.img> bin/dvx.exe ::DVX.EXE
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mcopy -s -o -i <floppy.img> bin/apps ::APPS
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```
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The `apps/` directory structure must be preserved on the target -- Program Manager
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recursively scans `apps/` for `.app` files at startup.
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## Documentation
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Each component directory has its own README with detailed API reference:
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- [`dvx/README.md`](dvx/README.md) -- GUI library architecture and API
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- [`tasks/README.md`](tasks/README.md) -- Task switcher API
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- [`dvxshell/README.md`](dvxshell/README.md) -- Shell internals and DXE app contract
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- [`apps/README.md`](apps/README.md) -- Writing DXE applications
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- [`rs232/README.md`](rs232/README.md) -- Serial port driver
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- [`packet/README.md`](packet/README.md) -- Packet transport protocol
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- [`security/README.md`](security/README.md) -- Cryptographic primitives
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- [`seclink/README.md`](seclink/README.md) -- Secure serial link
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- [`proxy/README.md`](proxy/README.md) -- Linux SecLink proxy
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- [`termdemo/README.md`](termdemo/README.md) -- Encrypted terminal demo
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