Mectov OS v24.0 — The DOOM Engine Update

The Mectov Kernel — an operating system kernel written from scratch in C and Assembly. No external libraries, no libc, no POSIX — every byte runs directly on hardware.

About

Mectov OS is a hobby operating system designed as a learning project and technical showcase. It boots via GRUB Multiboot, sets up protected mode with paging, and provides a fully graphical desktop environment with floating windows, custom static wallpapers, persistent draggable icons, hardware detection, standalone Ring 3 user applications, and real internet connectivity.

The v23.0 release delivers a massive performance and stability overhaul: Shadow Framebuffer rendering (delta-only MMIO writes), proper process lifecycle management with zombie detection and Ctrl+C signal support, a fully rewritten Snake game as a non-blocking WM app, smarter tab-completion, terminal input protection, and power menu bugfixes.

Created by M Alif Fadlan.

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Architecture

+--------------------------------------------------------------------+
|                       GRUB Multiboot (VBE)                         |
+--------------------------------------------------------------------+
|  boot.asm  -->  kernel.c  (kernel_main entry point)                |
+--------------------------------------------------------------------+
|  GDT (Ring 0+3)  |  IDT (ISR+IRQ)  |  TSS  |  Syscall (int 0x80)   |
+--------------------------------------------------------------------+
|  PIT Timer (1kHz) |  Keyboard (PS/2) |  Mouse (PS/2) |  Serial     |
+--------------------------------------------------------------------+
|  Memory Manager   |  VMM (Virtual Mem)|  IPC Message Queues        |
+--------------------------------------------------------------------+
|  Priority Thread   |  VFS + ATA PIO   |  PCI Scanner               |
+--------------------------------------------------------------------+
|  VGA/VESA Driver   |  Window Manager   |  RTL8139 NIC              |
+--------------------------------------------------------------------+
|  Network Stack (Ethernet/ARP/IPv4/ICMP/UDP/DNS)                    |
+--------------------------------------------------------------------+
|  MCT App Loader   |  Ring 3 User Tasks|  Display List Renderer     |
+--------------------------------------------------------------------+
|  Desktop (Squircle Icons) |  Taskbar (Glossy) |  Start Menu        |
+--------------------------------------------------------------------+
|  File Descriptors    |  UNIX Pipe           |  Login Screen         |
+--------------------------------------------------------------------+

Target Platform

• Architecture: i386 (32-bit x86), Monolithic Kernel
• Ring Levels: Ring 0 (Kernel) + Ring 3 (User Mode) — ACTIVE and Stable
• Scheduler: Preemptive Priority Round-Robin, Ring-Aware Context Switching
• Display: VESA VBE Linear Framebuffer, 1024x768, 32-bit color
• Storage: ATA PIO (IDE), 1MB virtual disk
• Audio: PC Speaker via PIT Channel 2
• Bus: PCI Configuration Space (ports 0xCF8/0xCFC)
• Network: RTL8139 NIC (virtual, via QEMU)
• Serial: COM1/COM2 UART 16550A (38400 baud, 8N1)

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Core Subsystems

1. Modern Mouse Cursor (src/drivers/vga.c)

• High-Resolution Bitmap: Upgraded from 8x16 to a sleek 16x24 design.
• Premium Contrast: Black inner fill with a crisp white outline for maximum visibility on any background.
• Dynamic Drop Shadow: A real-time 50% alpha-blended shadow cast beneath the cursor for a depth effect.
• Zero Lag: Optimized drawing logic with dirty-region tracking.

2. Window Manager (src/gui/wm.c)

• Double-buffered rendering using fast memcpy with dirty region tracking.
• Z-ordered floating windows with proper overlap handling.
• Rounded corners (radius 8) on all windows for a modern look.
• Vibrant macOS-style "traffic light" control buttons with indicator symbols:
  • Close (vibrant red circle with 'X' symbol)
  • Minimize (vibrant yellow circle with '-' symbol)
  • Maximize (vibrant green circle with '+' symbol)
• Aero Snap: Drag windows to screen edges for automatic half-screen (left/right) or full-screen (top) snapping with saved geometry restore.
• Window Resizing: Drag any window edge or corner to resize. 8-directional edge detection with minimum size constraints (220×150).
• Window Close Callback: wm_close now notifies the terminal to kill child processes and reset state.
• Clean Flat Aesthetic: Removed heavy shadows around windows to focus on a crisp, modern UI.

3. Taskbar & System Tray (src/gui/taskbar.c)

• WiFi Status Indicator: Replaced the RAM bar with a classic 3-arc WiFi icon, representing the OS's network capability.
• "Mectov OS" Start button with vertical separator line for distinct UI partitioning.
• Glossy dark background with Catppuccin Mocha accent border.
• Icon-only window buttons: each open app shown as a 16x16 squircle icon matching the desktop style.
• System tray with:
  • CAPS indicator (vibrant red when active)
  • HDD activity LED (red flash on disk I/O)
  • Digital clock with day of week, adjusted for UTC+7 (WIB) timezone.

4. Real-time Rendering (kernel.c + src/drivers/vga.c)

• Shadow Framebuffer: Triple-buffer architecture (back_buffer → front_buffer_copy → VGA MMIO). Only pixels that actually changed are written to hardware, eliminating thousands of expensive KVM VM-Exits per frame.
• VSync Disabled: Removed VGA port 0x3DA polling which caused massive latency spikes under KVM virtualization.
• Forced 60Hz Loop: Constant 16ms redraw cycle with ultra-low render times (~4ms) thanks to delta-only copying.
• Microsecond Timing: Real-time FPS and render time measurement using PIT hardware counters.

5. Desktop Environment (src/gui/desktop.c)

• Custom Baked Wallpaper: Full-color 1024x768 image processed via Python build script.
• Professional Squircle Icons: High-end rounded-rect icons with minimalist glyphs and curated color palettes.
• Draggable Persistent Icons: Icon positions are saved to icons.cfg on the VFS and persist across system reboots.

6. Login Screen (src/gui/login.c)

• Graphical login with wallpaper backdrop and semi-transparent overlay.
• Password input field with masked characters (●) and shake animation on wrong password.
• CAPS LOCK indicator warning.
• Sound feedback (beep) on login events.

7. Virtual Memory Manager (src/sys/vmm.c + src/include/vmm.h)

• Frame Bitmap Allocator: Tracks 128MB of physical memory (32768 pages) with a compact bitmap for O(1) allocation/free.
• Per-Process Address Spaces: vmm_create_page_dir() creates new page directories, vmm_clone_page_dir() copies kernel mappings for fork-like scenarios, vmm_free_page_dir() tears down an address space.
• Page Mapping: vmm_map_page() / vmm_map_pages() / vmm_unmap_page() with automatic TLB invalidation on CR3 reload.
• Region Allocator: vmm_find_free_region() locates free virtual address ranges starting at 0x08000000.
• Foundation for future demand paging and Copy-on-Write (COW) for Ring 3 process isolation.

8. IPC — Inter-Process Communication (src/sys/ipc.c + src/include/ipc.h)

• Named Message Queues: Fixed-size 64-byte messages with a 16-deep circular buffer per queue.
• Create & Connect: ipc_create_queue(name) for server processes, ipc_connect_queue(name) for clients.
• Blocking Receive: ipc_receive() blocks the calling task until a message arrives, with tick-based timeout support.
• Non-blocking Send: ipc_send() returns -1 immediately if the queue is full.
• Enables service-oriented architecture and clean multitasking app ecosystem.

9. Priority Thread Scheduler (src/sys/task.c + src/include/task.h)

• 4-Level Priority Round-Robin: IDLE(0) < LOW(1) < NORMAL(2) < HIGH(3). Higher priority runnable tasks always run first; round-robin scheduling within the same priority level.
• Thread API: task_create_thread() spawns a thread within the same process (shared address space) using a pid/tid model. task_exit_thread() terminates the current thread.
• Sleep/Wake: task_sleep(ticks) suspends a task for a specified duration; task_wake() resumes it. Used for efficient blocking I/O and timing.
• Process Lifecycle: task_kill(tid) for external termination (used by Ctrl+C). Zombie process detection in SYS_GET_EVENT auto-kills orphaned tasks.
• True CPU Yielding: SYS_YIELD now executes sti;hlt;cli to properly surrender the CPU until the next scheduler tick.
• Full context switching: general-purpose registers, EFLAGS, ESP, and per-task page_dir pointer for VMM integration.
• Per-task dual stacks: 16KB kernel stack + 8KB user stack.
• IRQ0-driven scheduler tick (1000Hz) with cooperative yield via SYS_YIELD.

10. Network Stack (src/drivers/net.c + src/drivers/rtl8139.c)

• RTL8139 NIC Driver: Full driver with PCI bus mastering.
• Ethernet/ARP/IPv4/ICMP/UDP/DNS: Complete local stack.
• Terminal commands: ping [ip] and host [domain].

11. Persistent File System (src/sys/vfs.c)

• Virtual File System (16 file slots) with auto-save to disk.img via ATA PIO.
• Persistence Fix: Reliable saving for configuration files like icons.cfg.

12. File Descriptor Layer (src/sys/fd.c + src/include/fd.h)

• UNIX-style FD abstraction: Per-task file descriptor table (16 FDs per task, 128 global) wrapping VFS nodes.
• Typed descriptors: FD_TYPE_FILE, FD_TYPE_PIPE_READ, FD_TYPE_PIPE_WRITE, FD_TYPE_DEV.
• Reference counting: Global FD entries with ref_count for safe sharing between threads.
• UNIX Pipe support: do_sys_pipe() creates a unidirectional pipe pair for inter-process data streaming.
• Full syscall integration: sys_open, sys_read, sys_write, sys_close, sys_pipe all route through the FD layer.

13. MCT Application Runtime (.mct)

• Custom Binary Format: 16-byte header with magic number verification and entry point specification.
• Fixed-Base Mapping: Applications are mapped at virtual address 0x02000000 within their own isolated page directory.
• Privilege Isolation: Clean transition from Ring 0 to Ring 3 via iret, ensuring user apps cannot execute privileged instructions.
• Launch Arguments: The kernel can pass arguments (like filenames) to newly launched Ring 3 tasks, retrievable via SYS_GET_LAUNCH_ARG.
• Independent Stacks: Each Ring 3 task maintains separate 16KB kernel and 8KB user stacks.

14. User-Mode GUI API

• Direct Window Management: Ring 3 applications can now create, raise, and close their own GUI windows via syscalls.
• Graphics Primitive Syscalls: Accelerated SYS_DRAW_RECT and SYS_DRAW_TEXT for rendering directly into the application's window buffer.
• Event Polling & Persistence: SYS_GET_EVENT allows user apps to respond to window-specific mouse and keyboard input. It implements a two-phase close signal, giving apps a chance to safely save data to the VFS before terminating.
• Flicker-Free Updates: SYS_UPDATE_WINDOW ensures changes are committed to the display list and rendered during the next 60Hz frame sync.

15. Security & Pointer Validation (src/sys/syscall.c)

• Safe Syscall Entry: Every pointer passed from Ring 3 is validated via validate_user_ptr to prevent kernel memory corruption or unauthorized data access.
• Address Boundary Checks: Enforces strict memory boundaries (USER_MEM_LIMIT) for all syscall parameters.
• Zombie Cleanup: The kernel automatically detects and terminates Ring 3 processes whose GUI windows have been closed (if they refuse to exit voluntarily), preventing orphaned tasks and resource leaks.
• Privilege Separation: Use of Global Descriptor Table (GDT) and Task State Segment (TSS) to strictly enforce CPU privilege levels (Ring 0 vs Ring 3).

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Syscall API Reference

All syscalls are invoked via int 0x80. Register conventions: EAX=syscall number, EBX/ECX/EDX/ESI/EDI=arguments.

Core Syscalls (1–10)

#	Name	Description
1	SYS_PRINT	Print string. EBX=str_ptr, ECX=color
2	SYS_OPEN	Open/create VFS file. EBX=filename → return fd
3	SYS_READ	Read file. EBX=fd, ECX=buf, EDX=size → bytes read
4	SYS_WRITE	Write file. EBX=fd, ECX=buf, EDX=size → bytes written
5	SYS_CLOSE	Close file descriptor. EBX=fd
6	SYS_MALLOC	Allocate memory (Identity-mapped heap)
7	SYS_FREE	Free allocated memory
8	SYS_GET_TICKS	Get PIT timer tick count
9	SYS_YIELD	Yield CPU (sti;hlt;cli for true CPU surrender)
10	SYS_EXIT	Terminate current task

GUI Syscalls (11–17)

#	Name	Description
11	SYS_DRAW_RECT	Draw rectangle. EBX=win_id, ECX=x, EDX=y, ESI=(w<<16)|h, EDI=color
12	SYS_DRAW_TEXT	Draw text. EBX=win_id, ECX=x, EDX=y, ESI=str_ptr, EDI=color
13	SYS_GET_KEY	Get keyboard char (non-blocking) → char or 0
14	SYS_GET_MOUSE	Get mouse state → EAX=x, EBX=y, ECX=buttons
15	SYS_CREATE_WINDOW	Create window. EBX=x, ECX=y, EDX=w, ESI=h, EDI=title → win_id
16	SYS_GET_EVENT	Get window event. EBX=win_id, ECX=event_ptr (auto-kills zombie tasks)
17	SYS_UPDATE_WINDOW	Commit draw commands. EBX=win_id

Thread & Process Management (18–22)

#	Name	Description
18	SYS_THREAD_CREATE	Create thread. EBX=entry, ECX=priority, EDX=page_dir → TID
19	SYS_SLEEP	Sleep current task. EBX=ticks
20	SYS_GET_PID	Get current task ID
21	SYS_SET_PRIORITY	Set task priority. EBX=tid, ECX=priority
22	SYS_GET_PRIORITY	Get task priority. EBX=tid → priority

IPC — Inter-Process Communication (23–28)

#	Name	Description
23	SYS_IPC_CREATE	Create message queue. EBX=key → queue ID
24	SYS_IPC_SEND	Send message (blocking). EBX=qid, ECX=type, EDX=data, ESI=len
25	SYS_IPC_RECV	Receive message (blocking). EBX=qid, ECX=type_out, EDX=data_out, ESI=len_out
26	SYS_IPC_DESTROY	Destroy queue. EBX=qid
27	SYS_IPC_TRY_SEND	Non-blocking send. Returns 0/-1
28	SYS_IPC_TRY_RECV	Non-blocking receive. Returns 0/-1

Virtual Memory (29–31)

#	Name	Description
29	SYS_VMM_MAP	Map page. EBX=vaddr, ECX=paddr, EDX=flags
30	SYS_VMM_ALLOC	Allocate virtual page. EBX=vaddr, ECX=flags → vaddr or 0
31	SYS_VMM_FREE	Free virtual page. EBX=vaddr

UNIX Compatibility (32)

#	Name	Description
32	SYS_PIPE	Create pipe pair. EBX=pipefd[2] → return 0/-1

Extended System & Hardware (46–50)

#	Name	Description
46	SYS_GET_TASKS	Get list of running tasks
47	SYS_GET_WINDOWS	Get list of open windows
48	SYS_KILL_TASK	Force kill a task. EBX=tid
49	SYS_GET_LAUNCH_ARG	Get launch argument string. EBX=buf, ECX=max_len
50	SYS_CREATE_FILE	Directly create an empty file in VFS. EBX=filename

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Applications

Application	Type	Description
Terminal	Ring 3 (.mct)	Full terminal emulator with command execution and IPC stdout redirection
Nano Editor	Ring 3 (.mct)	Windowed text editor for VFS files with stable auto-save
File Explorer	Ring 3 (.mct)	Browse and open stored files
System Info	Ring 3 (.mct)	Live RAM, CPU, resolution, uptime, and MAC address
Task Manager	Ring 3 (.mct)	Monitor CPU, RAM, and kill active user processes
PCI Manager	Ring 3 (.mct)	Scrollable table of detected PCI hardware
Clock	Ring 3 (.mct)	Digital clock with WIB timezone
Snake	Ring 3 (.mct)	Modern grid-based snake game in WM window with gradient body, score, speed scaling
Mini Browser	Ring 3 (.mct)	Text-mode web browser via serial modem proxy
Hello Ring 3	Ring 3 (.mct)	Demo user-space app with isolated memory and GUI window
GUI Calculator	Ring 3 (.mct)	Standalone external GUI calculator
Power Options	Ring 0	Shut Down, Restart, and Log Out dialog with accurate button hit-zones
DOOM Engine	Ring 0 (Port)	Full integration of the legendary 1993 DOOM engine with graceful exit to desktop

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Build and Run

Requirements

• gcc (with -m32 support)
• nasm
• make
• qemu-system-i386
• python3 + Pillow

Commands

# Clean and build the OS
make clean && make

# Run in QEMU
./run.sh

Building User Applications (.mct)

User mode applications are written in C, compiled with gcc -m32, and processed into the .mct format:

1. Compile: gcc -m32 -march=i386 -fno-pie -ffreestanding -c app.c -o app.o
2. Link: ld -m elf_i386 -T apps/app.ld app.o -o app.elf
3. Format: python3 build_mct.py app.elf app.mct
4. Deploy: The Makefile automatically handles this and uses inject_vfs.py to bake the .mct binaries into disk.img.

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Version History

Version	Highlights
v24.0	DOOM Engine Port: Fully playable port of the classic 1993 DOOM engine integrated directly into the kernel. Features keyboard polling, double buffer to MMIO front buffer translation, graceful OS exiting (vga_force_sync), and proper process teardown.
v23.0	Performance & Stability: Shadow Framebuffer (delta-only MMIO), VSync removal, zombie process detection + auto-kill, task_kill() API, Ctrl+C signal, Ctrl key tracking, Snake rewritten as WM app, terminal prompt protection, smart tab-completion with trailing space/slash, carriage return support, history display fix, power menu restart fix, -no-reboot removal.
v22.0	Kernel Modernization: Virtual Memory Manager (per-process address spaces, page mapping, region allocator), IPC named message queues (non-blocking send, blocking receive with timeout), 4-level priority thread scheduling with sleep/wake API, and 14 new syscalls (VMM/thread/IPC).
v21.0	Premium UI Refinement: High-res sleek mouse cursor with dynamic shadow, classic 3-arc WiFi indicator in system tray, and return to forced 60Hz real-time rendering loop.
v20.0	Modern UI Modernization: Professional squircle icons, vibrant macOS buttons with symbols (X, -, +), taskbar separator, flat design removal of shadows.
v19.0	Modern UI Redesign: Glass-morphism icons, Catppuccin theme, rounded corners, glossy taskbar.
v18.0	External App Ecosystem: .mct format, syscalls, Ring 3 apps (Calculator).
v17.0	Terminus Bold font, Draggable icons, VFS persistence.

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License

MIT License

Created by M Alif Fadlan.

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