Prog8 - Structured Programming Language for 8-bit 6502/6510 microprocessors

Written by Irmen de Jong (irmen@razorvine.net)

Software license: GNU GPL 3.0, see file LICENSE

This is a structured programming language for the 8-bit 6502/6510 microprocessor from the late 1970's and 1980's as used in many home computers from that era. It is a medium to low level programming language, which aims to provide many conveniences over raw assembly code (even when using a macro assembler):

• reduction of source code length
• easier program understanding (because it's higher level, and way more compact)
• modularity, symbol scoping, subroutines
• subroutines have enforced input- and output parameter definitions
• various data types other than just bytes (16-bit words, floats, strings, 16-bit register pairs)
• automatic variable allocations, automatic string variables and string sharing
• constant folding in expressions (compile-time evaluation)
• conditional branches
• when statement to provide a 'jump table' alternative to if/elseif chains
• structs to group together sets of variables and manipulate them at once
• automatic type conversions
• floating point operations (uses the C64 Basic ROM routines for this)
• abstracting away low level aspects such as ZeroPage handling, program startup, explicit memory addresses
• various code optimizations (code structure, logical and numerical expressions, unused code removal...)
• inline assembly allows you to have full control when every cycle or byte matters

Rapid edit-compile-run-debug cycle:

• use modern PC to work on
• quick compilation times (less than 1 second)
• option to automatically run the program in the Vice emulator
• breakpoints, that let the Vice emulator drop into the monitor if execution hits them
• source code labels automatically loaded in Vice emulator so it can show them in disassembly
• the compiler includes a virtual machine that can execute compiled code directy on the host system without having to actually convert it to assembly to run on a real 6502. This allows for very quick experimentation and debugging

It is mainly targeted at the Commodore-64 machine at this time. Contributions to add support for other 8-bit (or other?!) machines are welcome.

Documentation is online at https://prog8.readthedocs.io/

Required tools:

64tass - cross assembler. Install this on your shell path. A recent .exe version of this tool for Windows can be obtained from my clone of this project. For other platforms it is very easy to compile it yourself (make ; make install).

A Java runtime (jre or jdk), version 8 or newer is required to run a prepackaged version of the compiler. If you want to build it from source, you'll need a Java SDK + Kotlin 1.3.x SDK (or for instance, IntelliJ IDEA with the Kotlin plugin).

It's handy to have a C-64 emulator or a real C-64 to run the programs on. The compiler assumes the presence of the Vice emulator

Example code

This code calculates prime numbers using the Sieve of Eratosthenes algorithm::

%import c64utils
%zeropage basicsafe

~ main {

    ubyte[256] sieve
    ubyte candidate_prime = 2

    sub start() {
        memset(sieve, 256, false)

        c64scr.print("prime numbers up to 255:\n\n")
        ubyte amount=0
        while true {
            ubyte prime = find_next_prime()
            if prime==0
                break
            c64scr.print_ub(prime)
            c64scr.print(", ")
            amount++
        }
        c64.CHROUT('\n')
        c64scr.print("number of primes (expected 54): ")
        c64scr.print_ub(amount)
        c64.CHROUT('\n')
    }


    sub find_next_prime() -> ubyte {

        while sieve[candidate_prime] {
            candidate_prime++
            if candidate_prime==0
                return 0
        }

        sieve[candidate_prime] = true
        uword multiple = candidate_prime
        while multiple < len(sieve) {
            sieve[lsb(multiple)] = true
            multiple += candidate_prime
        }
        return candidate_prime
    }
}

when compiled an ran on a C-64 you'll get:

One of the included examples (wizzine.p8) animates a bunch of sprite balloons and looks like this:

Another example (cube3d-sprites.p8) draws the vertices of a rotating 3d cube:

If you want to play a video game, a fully working Tetris clone is included in the examples: