For the March 2019 Retrochallenge, I am continuing to work in kittyOS.  I accomplished a lot last time, and am adding more this month.

For full details, check my personal webpage http://mwsherman.com/rc2019/03/

The goal is to turn the CAT-644 into a 'real' computer.  And what I mean by that, is eventually I want to be able to turn it on, open a text editor, write some source code, compile, and run it, without turning on my PC.  To do this it needs a real operating system.

The Unix model is everything is a file.  This has been copied to death.  I am intentionally trying something different.  Instead, everything is a device.  A special device, a mux, lets a program select thru a collection of devices.  The plan, is the sdcard filesystem, is just a tree of virtual muxes, eventually selecting virtual block or char devices containing data.  You could call them directories or files.  But you don't need a traditional filesystem to get started;  The basic setup is a single mux containing a single device such as a serial port.

Hardware Drivers

The following is all working in the kittyOS hardware drivers.  Not all is bound to the OS by syscalls, but the driver's work on their own:

• Graphics
  • 248x240  64-color VGA graphics (with 640*480 timings)
  • Text output w/ scrolling
  • Sprite render
  • smooth 1px horz/vertical wraparound scrolling, with 'invisible' region
  • FAST (50% cpu) and SLOW (90% cpu) modes
• Serial
  • Up to 115k baud
• SDCard
  • recognize SD (not SDHC, SDXC) up to 2GB
  • read/write block
• PS/2 Keyboard
• Audio is supported (and tested) by the hardware, but not yet implemented in kittyos

Implemented and Working:

• Device driver tree
  • Mainmux device supporting:
    • character devices
      • PS/2 keyboard
      • VGA console
      • serial port
      • SPI port
      • planned: A 'file' is just a seekable chardevice accessible thru a tree of virtual muxes, stored on an sd card.
    • block devices
      • sdcard
        • init
        • read/write blocks
        • sdcard is controlled as spi device thru spi driver
    • mux devices (mux is a collection of devices)
      • the mainmux is the device thru which all other devices are reachable
      • muxes can switch other muxes
• 16-bit virtual machine interpreter
  • 16-bit accumulator-register machine
  • fastest possible dispatch: One 16-bit reg-reg arithmetic instruction per 6 AVR cycles (Can this be beat?  I've looked everywhere for a faster interpreter.  I can do in 8-bit machine with 5 cycles, but many programs want 16-bit math anyway)
• Handle-based memory allocator with automatic swapping between AVR internal memory and external SRAM.  (possible future support for disk-swapping or load-on-demand)
• 
  

Planned:

• interpreter-accessible syscalls for handle access
• Swappable handles containing code
• Storing chardevices on sdcard mux (finally 'files')
• Syscalls for sprites
• Audio support (eventually)