A Forth-based software development kit for the Sega Genesis/Megadrive platform. Currently at version 0. This is still a work-in-progress. Updates will be made to this Readme file when I have time and when I think of something to write down. Ask me questions!
Forth is a very powerful programming language/paradigm that you've probably never heard of. The best way to learn it is to read the book Starting Forth by Leo Brodie. First published in 1981, it remains today the best tutorial there is for the Forth programming language. The BlastForth repository contains a PDF copy, or you can read it online here:
https://www.forth.com/starting-forth/
You will need the Gforth compiler to build Genesis/Megadrive software with BlastForth. Gforth is available for all major desktop platforms (Linux, Mac, Windows) and can be downloaded from here:
https://gforth.org/
Linux users can also get Gforth from their distro's repositories, as it is a standard component of the GNU operating system.
See the Wiki Section to learn how to get started using BlastForth.
Like most Forths, BlastForth is NOT case-sensitive. Uppercase and lowercase letters are treated the same, so negate and NEGATE are equal to one another.
32-bit numbers are called cells, 16-bit numbers are half cells, and 8-bit numbers are called chars (characters). Words that operate on half-cells or chars have an "h" or "c" prefix. There is also limited support for 64-bit double cell numbers, and those words are prefixed with a "d" or a "2."
BlastForth is an indirect threaded Forth. The first cell of a definition contains a pointer to machine-executable code, and the remaining cells are the data field of the definition. The name and link fields exist only on the host machine; they are not present in the output ROM file.
Definitions surrounded by { } (curly braces) execute immediately on the host machine at compile time, instead of compiling and executing on the target machine. { } blocks are the equivalent of compile-time "macros." The standard word "immediate" is not supported; use { } instead.
"Host" machine refers to the desktop or laptop PC you write your programs with. The "target" machine is the Sega Genesis/Megadrive. Since BlastForth is a cross-compiler for a ROM-based system, it must distinguish between "compile time" and "run time" like a conventional compiler (native Forths do not typically make this distinction).
The M68000 CPU supports only 16-bit symmetric division. BlastForth's standard division operators (/, /mod, etc.) use a software fallback routine if the divisor doesn't fit in 16 bits. The Project Settings determine whether the compiler defaults to "symmetric" or "floored" division, with symmetric being the default.
Words enclosed in parentheses ( ), such as (init-video-config), are for internal use and should generally not be used outside of the source file they are defined in.
Words that end with an & (ampersand) return a code field containing raw machine instructions. Examples include docolon&, doconst&, and next&.
Words enclosed in < > (angle brackets) are the default implementation of a Deferred Word, such as <emit>. They need to be initialized at program start, i.e. ['] <emit> is emit.
Words defined with value or 2value do not have an initial value. Like all memory words, they must be explicitly given a value at program start.
Words that begin with a ? (question mark) generally leave their arguments on the stack. Words that end with a ? consume their stack arguments.