OS DEVELOPMENT

This repository contains resources for OS development, including KSDOS files and assembly (ASM) examples. It is intended for learning, experimentation, and exploring low-level system concepts such as memory management, boot processes, and hardware interaction.

KSDOS

16-bit real-mode x86 operating system written in NASM assembly, running in QEMU.

Architecture

• Bootloader + Kernel: bootloader/kernel/ksdos.asm — main kernel entry point
• 9 Overlays: CC, MASM, CSC, MUSIC, NET, OPENGL, PSYQ, GOLD4, IDE — loaded on demand via ovl_api.asm
• Build system: Makefile + tools/mkimage.pl — assembles all overlays and embeds them in a FAT12 disk image

Build

make        # build disk.img
make run    # run in QEMU (VNC on :0)
make deploy # package for Raspberry Pi (build/ksdos-watch.tar.gz)

Raspberry Pi Deployment

Files in raspberry/:

File	Purpose
setup.sh	One-time Pi setup: installs QEMU, configures TFT SPI overlay, compiles vkbd, installs service
launch.sh	Launch script: starts QEMU + virtual keyboard
vkbd.c	Virtual keyboard in C: framebuffer rendering + uinput key injection (no QMP socket)
ksdos-watch.service	systemd unit for auto-start on boot

Virtual Keyboard (vkbd.c)

• Renders a QWERTY keyboard on the bottom ~36% of the TFT framebuffer
• Reads touch events via Linux evdev (/dev/input/event*, auto-detected)
• Injects keypresses into QEMU using uinput (a kernel virtual input device)
• No QMP socket is exposed — no attack surface
• Build: gcc -O2 -o vkbd vkbd.c -lpthread
• The setup.sh script compiles it automatically on the Pi

Pi Setup

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"

Key Files

• bootloader/kernel/ksdos.asm — kernel main
• bootloader/kernel/opengl.asm — software graphics primitives (guarded with %ifndef)
• bootloader/kernel/ovl_api.asm — overlay loader API
• bootloader/kernel/compiler_asm.asm — defines str_no_space and compiler helpers
• tools/mkimage.pl — builds FAT12 disk image with overlays
• raspberry/vkbd.c — touch virtual keyboard (C, uinput)

BOOTLOADER EXAMPLES

Assembly language examples are available in the /examples directory.

The directory includes examples such as basic output:

• (HelloWorld.asm, PrintCharacters.asm) - character handling;
• (ClearScreen.asm, BackgroundColor.asm, TextFontColor.asm) - display controlling;
• (CheckRAM.asm) - simple interaction with memory.