BelowOSDev

Simple OS project for Dlang community and Kaktus Media! (Муну жаңылыктарга кошуп коюңуздарчы)

BelowOS: Bare-Metal D Kernel

BelowOS is a minimalist 32-bit x86 operating system built from scratch using the D programming language in -betterC mode. This project demonstrates system-level programming without a standard library or runtime, focusing on direct hardware interaction and manual resource management.

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Technical Architecture

1. Language and Runtime

The kernel is compiled using the -betterC subset of the D language. This ensures:

• Zero Runtime Overhead: No Garbage Collector (GC), TypeInfo, or ModuleInfo.
• Static Linking: The resulting binary is a freestanding ELF file capable of running directly on x86 hardware.
• Manual Memory Control: All memory operations are explicit, preventing hidden allocations.

2. Storage Subsystem (ATA PIO)

Storage is handled by a custom Integrated Drive Electronics (IDE) driver operating in Programmed I/O (PIO) mode.

• Direct Port I/O: Communication occurs via I/O ports 0x1F0 through 0x1F7.
• Sector Synchronization: The system implements a sync_to_disk() function that flushes the in-memory filesystem table directly to the disk sectors, ensuring persistence.

3. Static Filesystem (Static-FS)

The filesystem uses a flat-indexed structure to represent hierarchical data:

• Parent Indexing: Every file entry stores a parentIdx, allowing for directory navigation without complex pointer trees.
• Slot-Based Management: The filesystem is an array of fixed-size structures.
• The Nuke Mechanism: To ensure RAM efficiency, a dedicated "Nuke" routine performs a byte-level zeroing of memory slots, physically clearing data from the system's address space.

4. Video and UI

Output is managed via the VGA text buffer at memory address 0xB8000.

• 16-Color Palette: Uses a standard VGA attribute byte (4 bits for background, 4 bits for foreground).
• Type Safety: Core variables use size_t and ptrdiff_t to maintain architectural alignment and prevent overflow during memory addressing.

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Command Set

Command	Operation	Priority
ls	Scans the fs array for entries matching the currentDir index.	Standard
cd	Updates the currentDir pointer to the index of the target directory.	Standard
nuke	Mandatory Erasure. Zeroes out the name and content buffers in RAM and Disk.	Critical
cls	Fills the 0xB8000 buffer with empty characters and resets the cursor.	Utility
BSOD	Triggers a manual write of all cached filesystem entries to the HDD image.	System
and more)

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Development and Deployment

Build Requirements

• LDC2: LLVM-based D Compiler.
• NASM: For the 16-bit real-mode bootloader.
• GNU Make: Project automation.
• QEMU: Hardware emulation (i386).

Execution

1. Compile the bootloader and kernel using the provided Linker Script.
2. Generate a raw hdd.img file for storage emulation.
3. Launch via QEMU:

qemu-system-i386 -drive file=hdd.img,format=raw

or just type: make run

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Implementation Details

• Freestanding Environment: No dependency on libc or libphobos.
• Memory Mapping: Uses custom aliases for system-specific types to ensure portability across different x86 compilers.
• Hardware Reset: Implements a soft-reboot via the PS/2 controller (Port 0x64).

Алга Кыргызстан!