croOS

A complete operating system kernel written from scratch.

croOS is a full 32-bit x86 operating system with memory management, process scheduling, a virtual filesystem, TCP/IP networking, 42 system calls, and 16 built-in applications — all compiled from the Corros programming language (.cro files).

GitHub: github.com/CocoCopi/croOS

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Architecture

┌─────────────────────────────────────────────────────────────┐
│                       User Space                            │
│  ┌──────┐ ┌────────┐ ┌──────┐ ┌────────┐ ┌──────┐         │
│  │ Calc │ │ Snake  │ │Notepad│ │Browser │ │ ...  │  16 Apps │
│  └──┬───┘ └───┬────┘ └──┬───┘ └───┬────┘ └──┬───┘         │
│     └─────────┴─────────┴─────────┴──────────┘              │
│                        INT 0x80                              │
├─────────────────────────────────────────────────────────────┤
│                       Kernel Space                           │
│  ┌──────────────────────────────────────────────────────┐   │
│  │  Process Manager │ Scheduler │ 42 Syscalls           │   │
│  ├──────────────────────────────────────────────────────┤   │
│  │  VFS Layer  │  Ramdisk FS  │  FAT16 (TODO)          │   │
│  ├──────────────────────────────────────────────────────┤   │
│  │  TCP/IP Stack │ ARP │ ICMP │ TCP │ UDP               │   │
│  ├──────────────────────────────────────────────────────┤   │
│  │  PMM (bitmap) │ VMM (paging) │ Heap allocator        │   │
│  ├──────────────────────────────────────────────────────┤   │
│  │  GDT │ IDT │ ISR/IRQ │ PIC │ PIT Timer │ Keyboard   │   │
│  └──────────────────────────────────────────────────────┘   │
│                      0xB8000 VGA                            │
└─────────────────────────────────────────────────────────────┘

Kernel Features

Memory Management

• Physical Memory Manager (PMM): Bitmap-based page frame allocator, supports up to 128MB
• Virtual Memory Manager (VMM): x86 two-level page tables with identity mapping and user-space support
• Kernel Heap (kmalloc): First-fit allocator with block splitting and coalescing, 32MB heap

Process Management

• Round-robin scheduler with per-process priority
• 64 concurrent processes with independent page directories
• Context switching via saved register state (EIP, ESP, segment registers, EFLAGS)
• fork/exec support for process creation

Interrupt Handling

• 256 IDT entries — ISRs 0-31 (CPU exceptions) + IRQs 0-15 (hardware)
• ISR stubs in assembly, dispatching to C handlers
• PIC remapping — IRQ 0-7 → INT 32-47

Drivers

• VGA text-mode: 80x25, 16 colors, cursor control, scrolling, rectangle drawing
• PS/2 Keyboard: Scancode set 1, shift/ctrl/alt modifiers, ring buffer
• PIT Timer: 100 Hz tick, millisecond sleep
• Serial (COM1): Debug output for QEMU (-serial stdio)

Filesystem

• VFS layer: Mount-based routing, file descriptors, stat/mkdir/rmdir/rename
• Ramdisk: In-memory filesystem with create/read/write/delete, 64MB max

Networking

• TCP/IP stack: ARP resolution, ICMP echo (ping), TCP connections, UDP datagrams
• Ethernet frame I/O: Send/receive via NIC driver callback
• ARP cache: 16-entry LRU, automatic resolution

System Calls

• 42 system calls via INT 0x80
• File I/O, process management, memory allocation, VGA output, keyboard input, networking, power management

Built-in Applications (all in Corros .cro)

Key	App	Description
c	Calculator	Arithmetic: +, -, *, /
l	Calendar	Monthly calendar view
t	Clock	Live timer display
n	Notepad	Free-form text input
s	Snake	Classic snake game
r	Tetris	Falling block puzzle
g	2048	Slide tiles to 2048
m	Minesweeper	8x8 mine detection
p	Pong	AI opponent paddle game
b	Browser	Text-mode web browser
i	Image Viewer	VGA character graphics
k	Camera	VGA framebuffer capture
e	File Explorer	VFS directory navigation
x	Text Editor	Freeform text editing
d	Doc Viewer	Multi-format document viewer
a	App Manager	Installed apps list

Build

Prerequisites

apt-get install -y gcc-i686-linux-gnu nasm qemu-system-x86

Build the kernel

cd croOS
make

Run in QEMU

make run

Build for real hardware

make
# Write build/croOS.elf to disk partition
dd if=build/croOS.elf of=/dev/sdX bs=512

File Structure

croOS/
├── Makefile                    # Build system
├── linker.ld                   # Linker script
├── src/
│   ├── kernel/
│   │   ├── asm/
│   │   │   ├── boot.S          # Multiboot entry + stack
│   │   │   ├── gdt_flush.S     # GDT segment reload
│   │   │   └── isr.S           # 256 ISR/IRQ stubs
│   │   ├── gdt.c/h             # Global Descriptor Table
│   │   ├── idt.c/h             # Interrupt Descriptor Table
│   │   ├── process.c/h         # Process manager + scheduler
│   │   ├── kmain.c             # Kernel entry point + shell
│   │   └── types.h             # Fundamental types + port I/O
│   ├── mm/
│   │   ├── pmm.c/h             # Physical memory (bitmap pages)
│   │   ├── vmm.c/h             # Virtual memory (x86 paging)
│   │   └── kmalloc.c/h         # Kernel heap (first-fit free list)
│   ├── drivers/
│   │   ├── vga.c/h             # VGA text-mode (80x25)
│   │   ├── keyboard.c/h        # PS/2 keyboard (scancode set 1)
│   │   ├── timer.c             # PIT timer (100 Hz) + TSC
│   │   └── serial.c/h          # COM1 serial (QEMU debug)
│   ├── fs/
│   │   ├── vfs.c/h             # Virtual filesystem layer
│   │   └── ramdisk.c/h         # In-memory filesystem
│   ├── net/
│   │   ├── net.c/h             # TCP/IP stack (ARP/ICMP/TCP/UDP)
│   ├── sys/
│   │   └── syscall.c/h         # 42 system calls (INT 0x80)
│   └── libc/
│       └── string.c            # C standard library (string/math)
├── apps/
│   ├── calc.cro                # Calculator
│   └── ...
├── lib/
│   └── app.cro                 # App framework
├── doc/
│   └── APP_FORMAT.md           # App extension format docs
└── README.md

App Extension Format

• .cro — Corros source code
• .cropkg — Compiled Corros package (binary)
• .croapp — App metadata + compiled binary
• .exe — Windows compatibility layer
• .deb — Debian package compatibility
• .apk — Android package compatibility

Language: Corros

croOS is built with Corros, a self-hosting, bytecode-compiled programming language. The kernel's high-level logic is written in .cro files and compiled to C via corros --compile, then cross-compiled to i386 with GCC.

License

MIT