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 one—uncreatively dubbed Perl65—was quickly abandoned, but the Python one saw more work. When it came time to name it, 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.Ironically, cross-platform development for the Apple II is extremely difficult, and while Ophis has been very successfully used to develop code for the Commodore 64, Nintendo Entertainment System, and Atari 2600, it has yet to actually be deployed on any of the Apples which inspired its name. Ophis 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 Ophis 1.0 was formally released. However, Ophis was written for Python 2.1 and this became more and more untenable as time has gone by. As I started receiving patches for parts of Ophis, and as I used it for some projects of my own, it became clear that Ophis needed to be modernized and to become better able to interoperate with other toolchains. It was this process that led to Ophis 2. This is an updated edition of Programming With Ophis, including documentation for all new features introduced and expanding the examples to include simple demonstration programs for platforms besides the Commodore 64. It also includes updated versions of the To HLL and Back essays I wrote using Ophis and Perl65 as example languages.

As of this writing, the Ophis assembler is hosted at Github. The latest downloads and documentation will be available at . If this is out-of-date, a Web search on Ophis 6502 assembler (without the quotation marks) should yield its page.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. For Windows users, 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.

Versions of the examples in this book are available from the Ophis site. Windows users will find them packaged with the distribution; all other users can get them as a separate download or pull them directly from github. The code in this book is available in the examples/ subdirectory, while extra examples will be in subdirectories of their own with brief descriptions. Most examples will require use of platform headers—standardized header files that set useful constants for the target system and, if needed, contain small programs to allow the program to be loaded and run. These are stored in the platform/ subdirectory.