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uniOS Architecture

Boot Sequence

uniOS boots using the in-tree Meridian UEFI bootloader.

  1. Firmware starts EFI/BOOT/BOOTX64.EFI.
  2. Meridian loads kernel.elf and unifs.img from the EFI system partition.
  3. Meridian selects a GOP framebuffer mode.
  4. Meridian builds the uniOS BootInfo structure.
  5. Meridian creates initial higher-half page tables.
  6. Meridian exits boot services and jumps to the kernel entry point.

Boot Media

  • boot.img: The primary system disk image. It includes an EFI system partition and a dedicated, writable UNI_DATA FAT32 partition for persistent storage.
  • uniOS.iso: A UEFI-bootable ISO image for cross-platform compatibility and testing.

Both images support persistence by automatically mounting any discovered FAT32 volume labeled UNI_DATA to /data.

Kernel Startup

Upon entry, the kernel initializes core subsystems in order:

  • CPU features, GDT, and IDT.
  • Interrupt controllers (APIC/ACPI).
  • Memory management (PMM, VMM, and Heap).
  • Scheduler and threading.
  • Device drivers and VFS.
  • unifs.img mount (system root).
  • /data mount (persistent storage from FAT32 volume).
  • Userspace init launch.

Debug builds retain framebuffer and serial boot logs and run registered kernel tests. Release builds boot directly to the desktop session.

Memory Management

Physical Memory Manager (PMM)

Uses a bitmap-backed frame allocator initialized from the UEFI memory map. It tracks frame references for address space accounting and DMA safety.

Virtual Memory Manager (VMM)

Implements x86-64 four-level paging with higher-half kernel mappings. User processes occupy isolated lower-half address spaces. Supports MMIO, DMA, and page-level protection.

Kernel Heap

Provides bucketed allocation for small objects and page-backed ranges for large buffers, protected by kernel spinlocks.

Processes and Syscalls

Userspace programs are ELF binaries loaded from the VFS. The syscall interface provides:

  • Process lifecycle (fork, exec, exit, wait).
  • File and directory operations (open, read, write, stat).
  • Display and GUI composition.
  • Shared memory and inter-process signals.
  • TCP/UDP networking and DNS.
  • System power control (reboot, poweroff).

Desktop Session

/bin/init.elf initializes the graphical environment:

  • Window Manager: Desktop composition, window metadata, input focus, damage tracking, and wallpaper loading.
  • System Services: Menubar, Dock, and Desktop launcher.
  • Applications: Terminal, Files, Preferences, and Latitude.

Display & Graphics

The kernel display path handles framebuffer abstraction, dirty-region tracking, and compositor buffer submission. It supports framebuffer metadata from boot and provides display syscalls for presentation and event waiting.

Input Subsystem

Supports PS/2 keyboard/mouse (including IntelliMouse scroll) and USB HID keyboard/mouse via xHCI. Kernel-level event conversion provides unified input to the window manager.

Storage and Filesystems

  • VFS: Virtual filesystem switch abstraction.
  • uniFS: Read-only system filesystem for unifs.img.
  • FAT32: Persistent data storage with cluster-hinting and FSInfo optimization.
  • Drivers: ATA, AHCI, and USB Mass Storage (MSC).

Networking

Full-stack networking including Ethernet, ARP, IPv4, ICMP, UDP, TCP, DHCP, and DNS. Native drivers for e1000 and RTL8139 are included.

Audio

Supports AC97 and High Definition Audio (HDA) controllers with a native playback path in userspace.

Runtime Assets

The environment uses specialized binary formats to avoid heavy runtime parsing:

  • .uoic: Pre-rendered icon packages.
  • .uocu: Cursor packages with hotspot metadata.
  • .uof: Processed bitmap font data.
  • .uowp: Multi-variant wallpaper containers.