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KOS is an unofficial development environment for the SEGA Dreamcast game console with some support for the NAOMI and NAOMI 2 arcade boards.

KOS was developed from scratch over the internet by a group of free software developers and has no relation to the official Sega Katana or Microsoft Windows CE Dreamcast development kits. This has allowed it to fuel a thriving Dreamcast homebrew scene, powering many commercial releases for the platform over the years. It supports a signficiant portion of the Dreamcast's hardware capabilities and a wide variety of peripherals, accessories, and add-ons for the console, including custom hardware modifications that have been created by the scene.

Despite the console's age, KOS offers an extremely modern, programmer-friendly development environment, supporting C17 and C++20, with the majority of their standard libraries fully supported and additional support for many POSIX APIs. Additionally, KOS-ports offers a rich set of add-on libraries such as SDL, OpenGL, and Lua for the platform.


Core Functionality
  • Concurrency with Kernel Threads, C11 Threads, pthreads
  • Virtual filesystem abstraction
  • IPv4/IPv6 Network stack
  • Dynamically loading libraries/modules
  • GDB Debug stubs
Dreamcast Hardware Support
  • GD-Rom driver
  • Low-level 3D PowerVR Graphics
  • SH4 ASM-Optimized Math Routines
  • SH4 SCIF Serial I/O
  • DMA Controller
  • Flashrom Access
  • AICA SPU Sound Processor Driver
  • Cache and Store Queue Management
  • Timer Peripherals and Real-Time Clock
  • MMU Management API
  • BIOS Font Rendering
Peripherals and Accessory Support
  • Visual Memory Unit
  • Puru Puru Vibration Pack
  • Seaman Microphone
  • Dreameye Webcam
  • Lightgun
  • Keyboard
  • Mouse
  • Dial-up Modem
  • Broadband Adapter
  • LAN Adapter
  • VGA Adapter
  • SD Card Reader
Hardware Modification Support
  • IDE Hard Drive
  • 32MB RAM Upgrade
  • Custom BIOS Flashroms

Getting Started

A beginner's guide to development for the Sega Dreamcast along with detailed instructions for installing KOS and the required toolchains can be found on the Dreamcast Wiki. Additional documentation can be found in the docs folder.


Once you've set up the environment and are ready to begin developing, a good place to start learning is the examples directory, which provides demos for the various KOS APIs and for interacting with the Dreamcast's hardware. Examples include:

  • Hello World
  • Console Input/Output
  • Assertions, stacktraces, threading
  • Drawing directly to the framebuffer
  • Rendering with OpenGL
  • Rendering with KGL
  • Rendering with KOS PVR API
  • Texturing with libPNG
  • Bump maps, modifier volumes, render-to-texture PVR effects
  • Audio playback on the ARM SPU
  • Audio playback using SDL Audio
  • Audio playback using OGG, MP3, and CDDA
  • Querying controller input
  • Querying keyboard input
  • Querying mouse input
  • Querying lightgun input
  • Accessing the VMU filesystem
  • Accessing the SD card filesystem
  • Networking with the modem, broadband adapter, and LAN adapter
  • Taking pictures with the DreamEye webcam
  • Reading and Writing to/from ATA devices
  • Testing 32MB RAM hardware mod
  • Interactive Lua interpreter terminal


DCEmulation Forums: Goldmine of Dreamcast development information and history
Dreamcast Wiki: Large collection of tutorials and articles for beginners
Simulant Discord Chat: Home to the official Discord channel of KOS
IRC Channel: #dreamcastdev


A pseudo-operating system for the Sega Dreamcast. This repository is a mirror of the official SourceForge repository for KOS.






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