TOSX - The OS eXperiment

Welcome to The OS eXperiment project, an initiative to research OS development starting simple and complicating later.

This OS is a good candidate to be the foundation for a future homebrew computer.

Goals

• Multiplatform support - reached when running in two different archs. e.g. ARM + AVR
  • AVR 8bit microcontrollers
    • ATMega328p - 2KB RAM + 32KB FLASH
      • enough for initial experimentation, small programs and up to two or three simultaneous apps running
    • ATMega32u4 - 2.5KB RAM + 32KB FLASH
      • a bit more headroom for running apps
    • ATMega2560 - 8KB RAM + 256KB FLASH
      • starts to get interesting?
  • ARM CortexM4
    • STM32G431
    • STM32G474
    • TI LM4F120 (because it is available)
  • x86_32
    • QEMU
  • M68K
    • Sega Mega Drive/Genesis - future project
• Multitasking
  • Cooperative (might still be possible)
  • Preemptive (now preferred)
• Scheduling
  • Basic single level round-robin - Highly unoptimized for now :)
  • Support for async operations - e.g. I/O, time wait
• Basic Async/Await mechanism aimed for I/O
• Shell
  • Start new processes (blocking)
  • Start new processes (background)
  • Command line arguments to downstream processes
  • Better usability
  • More...
• Memory Management
  • Simple Allocator
    • Doubly-linked - a bit high on overhead
    • Merging of free blocks to reduce fragmentation
    • Best-fit search to reduce fragmentation
• Static stack allocation for tasks
• Heap stack allocation for tasks
• Sample apps
  • clear - clear screen
  • free - show memory stats
  • pi - calculates PI to 6digits
  • long - runs a long sleep (10s) to exercise async/await and timing
  • cdn - runs a countdown from 10, can be used to exercise multitasking
  • uptime - shows uptime since last reset (ugly output formatting)
• Filesystem
  • Basic ROM FS
• File support

Architecture (WIP)

  graph TD;
      A-->B;
      A-->C;
      B-->D;
      C-->D;

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