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A minimal Forth booter disk environment

branch: master
README.md

Preface

I like to do things myself. I've made several attempts to write a full fledged OS with nothing but assembly and my own toolchain, but this was my first success.

Prerequisites

NASM, Ruby, Bash or Sh, and qemu if you want to test the image.

Building

If you would like to try out a prebuilt binary, the "img" directory has you covered (disk.img is the full boot disk). Otherwise simply type:

  • ./build If this doesn't work, try putting the shell of your choice (it usually looks for bash) in front of build: sh build During building, you may notice something like
    • LAST: lbl19

If you've added/removed any words from any of the .f files, you need to change the call in NEXT.asm to the last label print. You also need to change the code that changes LAST to start from FLBL(whatever followed lbl).

Language

.f files are written in a mix between FORTH and a weird assembly syntax (8086). FORTH words are written between : and ; and native words are written between { and }. Spaces are necessary between every word. In the assembly, there are 4 additional words used for formatting and other hackery:

  • N - Write a newline
  • T - Write a tab
  • NT - Write a newline and a tab
  • FWORD - calls the respective word (if it's been defined) This isn't the cleanest syntax ever, but the amount of time saved from using this to generate a FORTH dictionary far outweighs readability, in my opinion.

Layout

  • beta.rb - This parses .f files
  • lexer.rb - A simple lexer for the parser
  • nametable.rb - A simple LUT for the interpreter
  • exec.rb - An executable frontend for beta.rb
  • chain - links all respective .f files properly
  • build - builds it
  • testimg - runs the image in qemu
  • DATA.f - data movement routines
  • IO.f - printing routines
  • LANG.f - dictionary routines
  • MATH.f - arithmetic routines
  • SYS.f - system routines
  • test.f - Extra routines, plus the "main" (GO in this case) routine
  • NUMBER.asm - converts a string to an integer on the stack
  • HEX.asm - converts an integer to a hex string
  • BOOT.asm - the bootloader
  • NEXT.asm - the Assembly that is run after the bootloader runs
  • HEADER.h - defines and calls used throughout the system Please note that a lot of my ASM is VERY messy

Using the System

  • Numbers are typed in 4 character hex strings, so 1 is 0001 and 255 is 00FF
  • Everything is in all caps
  • LIST-WORDS will list all - 1 of the words on the system
  • Everything is in reverse polish notation, so 1 + 1 would be 0001 0001 + on this system
  • LAST? prints the last words in the dictionary
  • DISK-READ and DISK-WRITE Read and write to the disk (USE AT YOUR OWN RISK) where the high byte is the track and the low byte is the sector (0102 DISK-READ would read track 1 sector 2 to DISKBUFFER). LOAD is disk-read, but it evaluates the first line. All disk IO is handled at DISKBUFFER
  • Compile time words start with a $. $IF and $THEN are examples of this.
  • This system NEEDS a legacy BIOS (If you're running this on real hardware, which I wouldn't recommend)
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