Tosin RTOS is a 32-bit x86 educational real-time operating system built from scratch in C and assembly. It boots via a custom 512-byte MBR bootloader, switches to protected mode, initializes timer interrupts, and runs a preemptive priority scheduler with a shell task.

The repository already includes a working end-to-end path:

• Bootloader loads kernel sectors from disk and enters protected mode.
• Kernel initializes memory management and scheduler.
• Idle and shell tasks are created at boot.
• Timer-driven preemptive scheduling is active.
• IPC primitives (semaphores and queues) are integrated.
• Interactive shell commands are available for runtime inspection and testing.

• Custom MBR bootloader in boot/boot.asm
• Real mode to protected mode transition with GDT setup
• A20 enable sequence
• Kernel load to physical address 0x8000
• Boot signature 0xAA55

• Kernel entry and low-level setup in kernel/core/entry.asm
• IDT setup and PIC remap
• PIT programmed for 100 Hz timer ticks
• Assembly context switching via context_switch

• Task model and lifecycle in kernel/core/task.c
• Scheduler in kernel/core/scheduler.c
• Preemptive, priority-based round-robin scheduling
• 16 priority levels (0 through 15)
• Tick-based sleeping with task_sleep

• Heap allocator in kernel/mm/memory.c
• Best-fit allocation strategy
• Block splitting and free-block coalescing
• 8-byte alignment
• Runtime usage stats via mem_get_total, mem_get_used, and mem_get_free

• Counting semaphores with wait queues in kernel/ipc/semaphore.c
• Circular-buffer message queues in kernel/ipc/queue.c
• Timeout-aware wait/send/receive APIs

• VGA text output and keyboard input in lib/io.c
• Command shell in shell/shell.c
• Built-in commands:
  • help
  • clear
  • meminfo
  • ps
  • echo
  • uname
  • test

System defaults are defined in include/config.h:

• MAX_TASKS: 32
• TASK_STACK_SIZE: 4096 bytes
• TIMER_FREQ_HZ: 100
• TIME_SLICE_MS: 10
• HEAP_SIZE: 1 MiB
• MAX_PRIORITY: 15
• QUEUE_SIZE: 16
• SHELL_BUFFER_SIZE: 256

This project is built with GNU toolchain-style utilities (Makefile uses dd, rm, ls). Recommended environments:

• Linux
• WSL on Windows

Required tools:

• nasm
• gcc with 32-bit support
• ld
• objcopy
• make
• qemu-system-i386 (for emulation)

Build:

make

Run:

make run

Debug (QEMU gdb stub):

make debug

Optional build verification script:

./build.sh

1. BIOS loads MBR at 0x7C00.
2. Bootloader in boot/boot.asm loads kernel sectors and enables protected mode.
3. Kernel entry in kernel/core/entry.asm sets interrupt/timer hardware.
4. Kernel main in kernel/core/main.c:
   • initializes heap
   • initializes scheduler
   • creates idle task (priority 0)
   • creates shell task (priority 5)
   • starts scheduler

• boot
• include
• kernel/core
• kernel/mm
• kernel/ipc
• lib
• shell
• docs

For deeper detail, see:

• docs/README.md
• docs/ARCHITECTURE.md
• docs/API.md
• docs/QUICKSTART.md
• docs/IMPLEMENTATION_SUMMARY.md

• 32-bit x86 only
• No user/kernel isolation
• No virtual memory or paging subsystem
• No filesystem or networking stack
• Shell is minimal and command set is intentionally small

Typical extension points:

• Add new shell commands in shell/shell.c
• Add or modify kernel services under kernel
• Tune system constants in include/config.h

Provided for educational and development use.