The Ophis project started on a lark back in 2001. My graduate studies required me to learn Perl and Python, and I'd been playing around with Commodore 64 emulators in my spare time, so I decided to learn both languages by writing a simple cross-assembler for the 6502 chip the C-64 used in both. The Perl version was quickly abandoned, but the Python one slowly grew in scope and power over the years, and by 2005 was a very powerful, flexible macro assembler that saw more use than I'd expect. In 2007 I finally got around to implementing the last few features I really wanted and polishing it up for general release. Part of that process has been formatting the various little tutorials and references I'd created into a single, unified document—the one you are now reading.

It's actually a kind of a horrific pun. See, I was using Python at the time, and one of the things I had been hoping to do with the assembler was to produce working Apple II programs. Ophis is Greek for snake, and a number of traditions also use it as the actual name of the serpent in the Garden of Eden. So, Pythons, snakes, and stories involving really old Apples all combined to name the assembler.

If you're reading this as part of the Ophis install, you clearly already have it. If not, as of this writing the homepage for the Ophis assembler is . If this is out-of-date, a Web search on Ophis 6502 assembler (without the quotation marks) should yield its page. Ophis is written entirely in Python and packaged using the distutils. The default installation script on Unix and Mac OS X systems should put the files where they need to go. If you are running it locally, you will need to install the Ophis package somewhere in your Python package path, and then put the ophis script somewhere in your path. Windows users that have Python installed can use the same source distributions that the other operating systems use; ophis.bat will arrange the environment variables accordingly and invoke the main script. If you are on Windows and do not have Python installed, a prepackaged system made with py2exe is also available. The default Windows installer will use this. In this case, all you need to do is have ophis.exe in your path.