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The Dreamcast shipped a stripped-down Windows CE 2.12 that retail games booted into and never exposed. Windows CE Dreamcast Community Edition takes that same on-disc CE runtime and turns it into something you can actually use: a multitasking windowed desktop and an in-progress TCP/IP stack over the Broadband Adapter — all baked into a standard bootable Dreamcast disc.

It is fully self-contained: the SH-4 PE compiler and the entire CE image toolchain are vendored in this repo. One cmake invocation goes from source to a bootable disc.gdi. No Platform Builder, no SDK install, no CD key.

Screenshots

The desktop	Multitasking
Icons, Start menu, taskbar, mouse cursor	Task Manager, Explorer browsing the disc, a live Clock — each app its own process

Features

• DCWin desktop shell — a windowed, multitasking desktop composited on the PVR2 / Direct3D: move / resize / minimize / maximize windows, a Start button, taskbar, and a mouse cursor. Every app runs in its own CE process.

• Built-in apps — Explorer (browse \, \Windows, \CD-ROM; launch binaries), Task Manager (live process + RAM view), Clock, Calculator, a memory tester, and a winsock network tester.

• Networking over the stock CE stack (work in progress) — a universal link shim (mppp.dll) aims to let the stock microstk.exe + winsock.dll run over Ethernet instead of dial-up PPP, with DHCP/ARP/DNS handled in the shim (DHCP option-6 → the Dreamcast's own flash ISP config → a public resolver). Both link backends — the Broadband Adapter and a W5500/MACRAW over SPI transport — are still being brought up and not yet working end-to-end.

• Self-contained CMake build — vendored SH-4 cl.exe + the CE image tools (makeimg, romimage, …). Produces retail (silent) or debug (serial console) images, and a standard bootable GDI.

Building

Prerequisites: CMake ≥ 3.20 and a generator (Ninja). The pair bundled with Visual Studio works out of the box — nothing else from VS is used. PowerShell is used for the disc-imaging steps (Windows host).

# configure (point -DCMAKE_MAKE_PROGRAM at ninja if it isn't on PATH)
cmake -G Ninja -S . -B build

# 1) just the SH-4 modules -> build/modules/  (dcspi.dll, mppp.dll, dcshell.exe, dcw* apps)
cmake --build build

# 2) the bootable OS image -> build/0winceos.bin
cmake --build build --target image

# 3) the full chain -> build/disc/disc.gdi
cmake --build build --target gdi

Build options

Option	Default	Effect
-DKERNEL=retail|debug	retail	retail = the silent kernel. debug = the SCIF serial-console kernel. Changes boot logging only.
-DDLLS=retail|debug	retail	retail = the stock OS DLLs (what real games run on). debug = the checked (assert-heavy) DLLs; these break some titles (e.g. DirectDraw/DDHAL), so leave this retail unless you're chasing a system-DLL bug.
-DAUTORUN=<exe>	dcshell.exe	The program launched at boot (HKLM\init Autorun). Use forward slashes for a path, e.g. -DAUTORUN=/CD-ROM/DC.EXE to autostart a disc binary.
-DEXTRADATA=<dir>	(none)	Folder whose contents are placed in the disc's \CD-ROM (e.g. a game's files). Relative paths resolve against the repo root; our OS image always wins for 0WINCEOS.BIN.

# example: a SCIF serial-console image (over the working retail DLLs) with a game on the disc
cmake -S . -B build -DKERNEL=debug -DEXTRADATA=path/to/game
cmake --build build --target gdi

Running

The build produces a standard multi-track build/disc/disc.gdi that boots on real Dreamcast hardware:

• GDEMU / MODE / USB-GD-ROM — copy the disc.gdi + its track files onto the SD card / image and select it from the menu.

• Burned disc — for a GD-R / GDEMU-exact layout, use toolchain/make-gdi-real.ps1 to rebuild against a real CE-game GDI (matches the original IP.BIN + track geometry).

The default image boots straight to the DCWin desktop. For diagnostics, build with -DKERNEL=debug and watch the Dreamcast serial (SCIF) console.

Repository layout

Path	What
CMakeLists.txt, cmake/	the entire build (modules → image → GDI)
shell/	the DCWin desktop shell, PVR2/D3D compositor, and the client apps
net/netif/	the universal mppp.dll link shim (BBA + W5500 backends, DHCP/ARP/DNS)
drivers/dcspi/	reusable SPI transport (SCI hardware-SPI + SCIF bit-bang) for the W5500
toolchain/	wrap-image.ps1 / make-gdi.ps1 / make-gdi-real.ps1 + the build README
vendor/sh-toolchain/	the SH-4 PE compiler + CE headers
vendor/wcesdk/	the vendored CE 2.12 SDK: headers, libs, image tools, OS modules, kernels

See toolchain/README.md for build internals.

Notes

This project builds on the Sega "Dragon" Windows CE for Dreamcast SDK (vendored). The shell, networking shim, and SPI driver are original work; the CE kernel and system modules are the stock SDK binaries. Don't redistribute the vendored SDK binaries outside the spirit of this research project.