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SquidgeOS

RISC-V Operating System.

Kernel Development Roadmap

Phase 1: Foundations & Memory Management (Current)

  • Bootstrapping: RISC-V entry.S and kernel entry point.
  • UART Driver: Basic serial communication for debugging.
  • Panic System: Kernel panic mechanism for fatal errors.
  • Physical Memory: Page-level allocator (free list based).
  • Kernel Heap: kmalloc/kfree with:
    • Splitting of large blocks.
    • Doubly-linked list headers.
    • Bidirectional coalescing (Iterative).
  • x ] String Library: Complete lib/string.c (memset, memcpy, strcmp, strlen).
  • Formatted Printing: Robust kprintf implementation for hex and decimal.

Phase 2: Hardware Interfacing & Traps

  • Trap Handling:
    • Setup mtvec (Machine Trap Vector).
    • Assembly "trampoline" to save/restore registers.
    • C dispatcher for exceptions and interrupts.
  • Timer Interrupts:
    • Interface with RISC-V CLINT (Core Local Interrupter).
    • Implement a system heartbeat (ticks).
  • External Interrupts: Setup PLIC (Platform-Level Interrupt Controller).
    • Keyboard Driver (Input Buffer & Scancode Processing)

Phase 3: Multitasking & Scheduling

  • Task Structure: Define task_struct (PID, State, Stack Pointer, Priority).
  • Context Switching: Assembly logic to switch register sets between tasks.
  • Scheduler:
    • Implement a Round-Robin scheduling algorithm.
    • Task lifecycle management (Create, Yield, Terminate).
  • Synchronization: Basic Spinlocks or Semaphores for resource protection.

Phase 4: Virtual Memory

  • Sv39 Paging:
    • Walk the 3-level page table structure.
    • Map/Unmap functions for virtual addresses.
  • Kernel/User Separation: Isolate kernel memory from user processes.
  • Higher Half Kernel: Remap kernel to upper virtual memory.

Phase 5: Userspace & System Calls

  • User Mode Jump: Switch CPU to User (U) mode.
  • ECALL Interface:
    • Implement system call dispatcher.
    • Basic syscalls: write, exit, getpid, fork.
  • ELF Loader: Read and execute simple static binaries.

Phase 6: Filesystem & Shell

  • VFS Layer: Abstract File System interface.
  • Initial RAM Disk (initrd): Load basic files into memory.
  • User Shell: Interactive CLI to execute commands and scripts.