M64 was written in 1997 to allow the Commodore 64 to function as a standalone synth module, producing sound in realtime driven by signals from a midi interface. M64 features a built in editor for programmable sounds and a virtual machine to execute the code that produce sound.
An extensive manual is available in the following formats.
The manual explains how to get the files to your Commodore 64 via Midi if necessary.
A small change in the flowchart has been made from the original manual since Autoboy/Hack'n Trade pointed out it was wrong. localAlways is executed before globalAlways. This is reflected in all manuals except in the GEOWrite manual.