gizmOS

A RISC-V 64-bit kernel written in C

gizmOS is a minimal RISC-V 64 kernel that provides foundational OS capabilities with a focus on hardware abstraction and memory management.

Features

• Hardware interfaces

  • UART for serial communication
  • Framebuffer support with flanterm terminal emulation
  • Real-time clock (RTC)
  • Platform-Level Interrupt Controller (PLIC)

• Memory management

  • Physical page allocator
  • Virtual memory with SV39 paging
  • MMIO mapping

• System facilities

  • Formatted output (printf-like functionality)
  • String manipulation
  • Time functions with sleep capabilities
  • Basic math functions

• Exception and interrupt handling

  • Trap framework
  • External interrupts

• Device Tree Blob (DTB) parsing

  • Initial loading and parsing via smoldtb
  • Hardware detection support

• Testing framework

  • Physical allocator tests
  • Trap/exception tests

Building

Prerequisites

• LLVM/Clang toolchain (with RISC-V support)
• GNU Make
• LLD linker

First, download the dependencies:

cd kernel/
chmod u+x get-deps
./get-deps

Note

You may need to adjust the compiler path in kernel/GNUmakefile to match your system configuration.

To build the kernel:

make

To build the kernel and run it in QEMU:

make run

If you desire to enable debugging features, uncomment the DEBUG := 1 line in kernel/GNUmakefile and GNUmakefile. Then, you can use make run and also use ./dbg.sh to automatically attach LLDB to gizmOS and set a breakpoint on the trap handler.

Project Structure

• kernel/ - Kernel source code
  • src/ - Main source files
    • device/ - Device drivers (UART, framebuffer, console, PLIC, RTC)
    • dtb/ - Device Tree Blob parsing
    • lib/ - Core libraries (memory, strings, time, math, formatting)
    • extern/ - External libraries
      • flanterm/ - Framebuffer terminal
      • smoldtb/ - Device tree parser
    • tests/ - Test suites for various components
    • *.c/*.h - Core kernel implementation (memory management, paging, etc.)

Development

gizmOS is a work in progress. Key areas for future development include:

• Advanced memory allocation (beyond basic page allocation)
• Process management
• Filesystem support
• More comprehensive device drivers
• User-space support

Contributions are welcome!