KSDOS v2.0

A 16-bit real-mode x86 operating system written in NASM assembly, inspired by MS-DOS. Runs in QEMU and deploys to Raspberry Pi with a TFT touchscreen.

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Features

• FAT12 filesystem — full read/write support, root directory, subdirectories, cluster chains
• 42 overlay modules — compilers, games, tools, and drivers loaded on demand from disk
• SYSTEM32 directory tree — embedded MS-DOS 4.0 reference sources (INC, H, DOS, BIOS, CMD, DEV, MEMM)
• Enhanced VGA boot screen — full-color direct VGA text buffer rendering with animated progress bar
• Full disk installer — copies all 2880 sectors to SSD/HD via BIOS EDD (LBA) with CHS fallback
• 3-disk installer set — MS-DOS-style installation flow across three floppy images
• Raspberry Pi deployment — auto-starts via systemd, TFT SPI framebuffer, uinput virtual keyboard

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Architecture

bootloader/
  boot/
    bootsect.asm      FAT12 boot sector (512 bytes) — loads KSDOS.SYS into 0x1000:0000
    mbr.asm           Master Boot Record
  kernel/
    ksdos.asm         Kernel entry point + jump table + module includes
    splash.asm        VGA boot screen (direct 0xB800 writes, animated progress bar)
    fat12.asm         FAT12 filesystem driver
    disk.asm          BIOS disk I/O (EDD + CHS fallback)
    install.asm       Full-disk installer (copies all 2880 sectors to SSD/HD)
    shell.asm         Command shell
    video.asm         VGA text + Mode 13h graphics driver
    ovl_api.asm       Overlay loader API
    mass_loader.asm   Mass overlay pre-loader
    overlays/         42 overlay .OVL modules (see below)
    SYSTEM/           MS-DOS 4.0 reference source tree
tools/
  mkimage.pl          FAT12 disk image builder (Perl)
raspberry/
  setup.sh            One-time Pi setup
  launch.sh           QEMU launch script
  vkbd.c              Touch virtual keyboard (C, uinput)
  ksdos-watch.service systemd unit

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Overlays

All overlays are loaded on demand by the kernel overlay API and executed at 0x7000.

Category	Overlays
Compilers	CC, MASM, CSC, JAVA, PY, PERL, PHP, VB, DELPHI, JS, HOLYC
Dev Tools	IDE, PSYQ, GOLD4, AI
System	NET, OPENGL, MUSIC, RING0HW, MATRIX, SYSINFO, CALC, COLOR
Games	PONG, SNAKE, TETRIS, BRKOUT, INVADE, ASTRO, MAZE, TANKS, RACE, CHESS, MINE, DUNG, FROG, LINES, SIMON, CONN4, WORM, GOLF, SHOOT, ROGUE

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Boot Screen

The boot screen (splash.asm) writes directly to the VGA text buffer at 0xB800:0000 — no ANSI.SYS dependency. Features:

• Full blue background with centered ASCII art logo
• Bright white / cyan / yellow color scheme
• Animated progress bar using CP437 block characters (█ fill, ░ empty)
• Per-stage status messages (FAT init → root dir → disk subsystem → drivers → ready)
• Bottom status bar updates when the shell starts

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Installation (SSD / HD)

The install_to_hd routine in install.asm copies the complete 2880-sector disk image (1.44 MB) to the internal hard disk or SSD (BIOS drive 0x80).

• Uses INT 13h AH=43h EDD (LBA) as primary method — works on all modern BIOS/UEFI-CSM
• Falls back to CHS (63 SPT / 255 heads) if EDD is unavailable
• install_to_ssd is an alias — SSDs appear identically to HDDs under BIOS
• Previous versions only copied 1 sector (the MBR), causing "KSDOS.SYS not found" on reboot — this is now fixed

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Build

Requirements: nasm, perl, qemu-system-i386, make

make              # build build/disk.img (full system)
make disks        # build all 3 installer disk images
make run          # boot in QEMU (VNC on :0)
make run-sdl      # boot in QEMU (SDL window)
make run-serial   # boot in QEMU (serial/headless)
make run-disk1    # boot installer Disk 1 in QEMU
make deploy       # package for Raspberry Pi → build/ksdos-watch.tar.gz
make clean        # remove build/

3-Disk Installer

disk1.img   Disk 1 — initial setup, Ring0 hardware overlay
disk2.img   Disk 2 — system files
disk3.img   Disk 3 — full KSDOS system (copy of disk.img)

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Raspberry Pi Deployment

make deploy
scp build/ksdos-watch.tar.gz pi@<IP>:~/
ssh pi@<IP> "tar xzf ksdos-watch.tar.gz && sudo bash ksdos-watch/setup.sh && sudo reboot"

setup.sh installs QEMU, configures the TFT SPI framebuffer overlay, compiles vkbd, and installs the systemd service.

Virtual Keyboard (vkbd.c)

• Renders a QWERTY layout on the bottom ~36% of the TFT framebuffer
• Reads touch events from Linux evdev (/dev/input/event*, auto-detected)
• Injects keypresses into QEMU via uinput (no QMP socket — no attack surface)
• Build: gcc -O2 -o vkbd vkbd.c -lpthread

File	Purpose
setup.sh	One-time Pi setup: QEMU, TFT overlay, vkbd compile, service install
launch.sh	QEMU + virtual keyboard launch script
vkbd.c	Touch virtual keyboard (C, uinput)
ksdos-watch.service	systemd unit for auto-start on boot

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Key Files

File	Description
bootloader/boot/bootsect.asm	FAT12 boot sector — finds and loads KSDOS.SYS
bootloader/kernel/ksdos.asm	Kernel entry point, jump table, module includes
bootloader/kernel/splash.asm	VGA boot screen with direct buffer writes
bootloader/kernel/install.asm	Full-disk SSD/HD installer (2880 sectors)
bootloader/kernel/fat12.asm	FAT12 read/write filesystem driver
bootloader/kernel/ovl_api.asm	Overlay loader and mass-loader API
bootloader/kernel/opengl.asm	Software graphics primitives (Mode 13h)
bootloader/kernel/shell.asm	Interactive command shell
tools/mkimage.pl	FAT12 disk image builder with SYSTEM32 tree embedding
raspberry/vkbd.c	Touch virtual keyboard for Pi TFT screen