proOS

proOS is a BIOS/MBR 32-bit hobby operating system made by me!

Repository Layout

• boot/mbr.asm – 512-byte MBR that loads the stage-2 loader
• boot/stage2.asm – real-mode loader that switches to 32-bit protected mode, loads the kernel and a FAT16 disk image, and passes VBE framebuffer info to the kernel
• kernel/ – kernel sources (entry stub, linker script, VGA, shell, RAMFS, interrupts, drivers, scheduler)
• kernel/vbe.c|h – framebuffer driver and text console shim
• kernel/gfx.c|h – minimal compositor and demo windows
• kernel/fat16.c|h – in-memory FAT16 reader used for lsfs/catfs
• kernel/memory.c|h – bump allocator backing window buffers
• kernel/fat16_image.c – host helper that generates build/fat16.img for Stage 2 to load
• iso/make_iso.sh – helper to wrap the raw image in an El Torito ISO
• Makefile – builds the bootloader, kernel, and raw disk image
• tests.md – manual tests for this phase

Prerequisites

Use MSYS2/WSL2 or another Unix-like environment on Windows. Install:

• nasm
• i686-elf cross toolchain (i686-elf-gcc, i686-elf-ld, i686-elf-objcopy)
• xorriso (for ISO creation)
• qemu-system-i386 (optional, for quick testing)
• gcc (host compiler used to build the FAT16 image helper)

Ensure the cross toolchain binaries are on your PATH.

Build

make

Outputs land in build/:

• proos.img – bootable raw disk image
• kernel.elf / kernel.bin – linked kernel artifacts
• mbr.bin, stage2.bin – boot stages
• fat16.img – 16 KB read-only FAT16 volume preloaded with readme.txt

Create an ISO (requires xorriso):

make iso

The script writes build/proos.iso.

Clean artifacts:

make clean

Run in QEMU

make run-qemu

Expected Boot Flow

1. mbr.asm loads stage2.asm into 0x7E00.
2. Stage 2 loads the kernel into 0x00010000, enables the A20 line, enters protected mode, copies the kernel to 0x00100000, and jumps to _start.
3. _start (from crt0.s) sets up the stack and calls kmain.
4. kmain initializes VGA text mode, prints a banner, initializes the RAMFS stub, and starts the shell.
5. The shell waits for keyboard input (IRQ-driven) and supports:
   • help
   • clear
   • echo <text> / echo <text> > <file>
   • mem
   • reboot
   • ls
   • cat <file>
   • proc_list
6. Cooperative scheduler boots a user init process that spawns a user echo_service via syscalls and demonstrates IPC (ECHO: Hello banner at boot).
7. FAT16 image is copied to 0x00200000 and exposed via lsfs / catfs shell commands.
8. When gfx is entered, the framebuffer compositor draws a demo desktop with windowed output; keyboard input remains routed to the shell.

Known Limitations

• FAT16 support is read-only, limited to 8.3 filenames in the root directory.
• Framebuffer path assumes a 32-bpp VESA mode; systems without that support fall back to VGA text automatically.
• mem reports hard-coded values.
• RAMFS remains a stub for scratch files.
• reboot relies on controller reset and may fall through to an infinite hlt if unsupported.