1. Introduction
2. What You Will Need
3. Installation
4. Games
5. Starting A Game
6. Keyboard Layout
7. Game Properties
8. Real Paddle Adaptor
9. Acknowledgments
10. License and Disclaimer

A Brief History of the Atari 2600

In the early 1970's, video arcade games gained commercial success for the first time. The American public was introduced to Pong, Tank, and other interactive video games which populated amusement parks, bars, and arcades. The games were successful enough to create interest for home versions, so in 1975 Atari released Home Pong and it was a smash hit. Other companies such as Magnavox and Coleco followed suit and released their own dedicated console games. Then in 1976, Fairchild Camera and Instrument introduced the Channel F system, the first cartridge based home video game system. The industry recognized that cartridge systems were the future of video gaming, and began development in that direction. In January 1977, RCA released the Studio II, another cartridge based system, although it only projected in black and white and seemed to be focused on educational titles. Then, in October 1977, Atari released the Atari VCS (Video Computer System) with an initial offering of nine games. This system, later renamed the Atari 2600, took the industry by storm and dominated the marketplace for years to come.

Because of oversupply, the Christmas season of 1977 was very rough on the video game industry, and the Atari 2600 was the only system that managed to emerge unscathed. Atari enjoyed strong sales in 1978 and a fantastic holiday season, as Atari released more games such as Outlaw, Spacewar, and Breakout. Internally however, Atari was at odds. Nolan Bushnell, the inventor of pong and founder of Atari, wound up leaving the company and purchased Pizza Time Theater, which later became the successful Chuck E. Cheese! In 1979 Atari continued their trend and released 12 more games which met with continued success. However, Atari was now facing some stiffer competition from the Mattel Intellivision and the Magnavox Odyssey2.

Atari needed a mega-hit in 1980 in order to squash the competition, and they found it in the home version of a game from Japan called Space Invaders. It was so popular that people were buying the Atari 2600 just so they could play Space Invaders at home. Following that, Atari released Adventure, which was the first video game to contain an Easter Egg - placing an object in a certain area revealed the programmer's name, Warren Robinett. 1980 was important for another reason - the creation of the first ever third party software producer, Activision. The company was formed by four Atari employees who were unsatisfied with the working conditions at the company. They released four games initially: Dragster, Fishing Derby, Checkers and Boxing. The games were very well received by the public, and revealed that the Atari 2600 was capable of better games than Atari themselves had been producing. Atari tried to prevent Activision from selling games, but they failed and Activision grossed $70 million that year.

By 1981, the video game industry was basically a horse race between the 2600 and the Intellivision. While the Intellivision was technologically superior in some respects, the 2600 continued to lead in sales. Atari released the home version of Asteroids, which was a huge success. Inspired by the success of Activision, another software development group called Imagic was formed. They would not release any games until 1982 however. Another company, Games by Apollo, was formed in Texas and released several games that year.

Coleco entered the market in 1982 with the release of the graphically superior Colecovision. To combat this new system, Atari produced the 5200, a technologically comparable system. The 2600 dropped $100 in price in order to remain competitive. Then a company called Arcadia released a peripheral called the Supercharger which played games in an audio cassette medium. This allowed for multiple loads and expanded the 2600's capabilities.

Atari released Pac-Man and E.T. that year, two incredibly hyped games which were critical flops. Although Pac-Man sold many copies, it was considered to be a poor translation of the arcade hit. However, there were many fantastic games produced for the 2600 during this period, and it was still selling strong.

Ever since the inception of Activision, Atari had been fighting to keep third parties from producing cartridges which they felt were stealing profits from them. Finally the issue was settled when Atari agreed to allow third party manufacturing in exchange for a royalty. Suddenly software companies began popping up all over, and 1982 saw releases from companies like Venturevision, Spectravision, Telesys, CBS, 20th Century Fox, US Games, M Network, Tigervision, Data Age, Imagic and Coleco. There was even a company that released a line of X-Rated games for the 2600 called Mystique. The year was financially successful for Atari, however there seemed to be a glut of software. Although there were many quality titles still produced, there was an increasing number of rushed games as manufacturers attempted to cash in on the craze.

More companies jumped on the band wagon in 1983. Zimag, Ultravision, Amiga, and others were also producing games and peripherals. It seemed as if there was just too much product to meet the demand, and as it turned out there was. By the end of the year, companies began folding. US Games, Data Age, Games by Apollo, Telesys and others all closed their doors from poor sales. A video game crash was occurring, and all companies were taking it on the chin.

1984 was a much more subdued year for the Atari 2600, and the price of the system had now dropped to $40-$50. Many were saying that the video game industry was dead. However, Atari surprised everyone by announcing the release of the 7800, and also promising more 2600 games with improved graphics and sound. Unfortunately, neither of these things happened in 1984 because Atari sold their home video game division to Jack Tramiel who believed that home computers would replace video game systems. No further mention of the 2600 or 7800 was made that year, and it appeared that they might be dead.

1985 was another very quiet year for Atari and video games in general, and only a few games were released for the 2600. Activision produced Cosmic Commuter and Ghostbusters, but with little fanfare or marketing, these games did not sell well. However, because of the huge game library and cheap price, Atari still sold over a million 2600 consoles in 1985.

There were very few plans for home video game systems by any company in 1986, since the market appeared to be dead. Then, to most people's surprise, Nintendo brought the NES to America and it was a smash hit, proving that video games still had a place in the US. Atari decided that maybe it would be a good idea to release the 7800 units it had in storage, and produce some more 2600 games. The 7800 was released with only 3 games initially available, although it was compatible with the 2600 library. They also redesigned the 2600 as the 2600 Jr., a machine with the same abilities, but a new look and marketing campaign. It was sold for less than $50.

Video games were once again selling phenomenally in 1987. Atari released several new titles, including Jr. Pac-Man, and also licensed a number of games from other companies such as Donkey Kong and Q*Bert. These new titles sold for $10-$15. Interestingly, a number of titles began appearing again from third part companies such as Epyx, Froggo, and Exus. It seemed that the 2600 was not dead yet!

In 1988, Atari rehired Nolan Bushnell and announced a number of new titles, including Secret Quest, a game written by Mr. Bushnell himself. Atari continued to manufacture these games even until 1989. However, it was apparent that the 2600, after its introduction over a decade ago, was finally at the end of its run. Although it was still produced and marketed outside of the US, the Atari 2600 finished its run in America. No other console has had such a long history or sold as many systems in the U.S.

Today, the 2600 still has a large number of fans who remember the countless games played over the years, and the years to come. There are even games being produced by hobbyists, some of them quite professionally, being released on newly burnt cartridges with labels and manuals. And the recent trend in retrogaming has brought many more video game fans to rediscover the 2600, and it continues to live on 22 years after its release!

Alexander Bilstein
February 1999

1. Introduction

Stella is a freely distributed multi-platform Atari 2600 VCS emulator; originally developed for Linux by Bradford W. Mott. Stella allows you to enjoy all of your favorite 2600 games once again by emulating the 2600's hardware with software. Stella is written in C++, which allows it to be ported to other operating systems and architectures. Since its original release Stella has been ported to AcornOS, AmigaOS, DOS, FreeBSD, Linux, MacOS, OpenStep, OS/2, Sega Dreamcast, Unix, and Windows.

New in Release 1.3

• Improved TIA sound system so that games with digitized audio work
• Added saving and loading of game state to the core; X11, SDL, and DOS versions current support saving and loading game state
• Added support for F4 bankswitching method
• Pitfall II DPC sound emulation completed
• Fixed a bug which caused the difficulty switches to operate backwards
• Changed DPC auto-detection to use file size so that Pitfall II mods work
• Modified RIOT timer emulation so that startup values are random
• Added 3F bankswitching auto-detection routine so that homebrews and demos work without a stella.pro entry
• Updated the TIA message boxes so they look a little nicer
• Latest stella.pro file included in distribution
• Added some developer options to the core, and the ability to change game width, height, xstart, ystart, etc. while the emulation is running. Added ability to switch between NTSC and PAL at runtime, and the ability to save the current properties to a file or to merge the changes into the stella.pro file; X11 and SDL versions supported for now
• Added save/load state ability to the core; X11 and SDL versions supported for now
• External sound server for the X11 and SDL versions no longer required, as all sound code is now integrated into the core
• Changed the locations of the users' config files for the X11 and SDL versions; the users' stellarc file is now located in "$HOME/.stella/stellarc", state files are located in "$HOME/.stella/state/" and the stella.pro file is located in "$HOME/.stella/stella.pro"
• Changed the way options are supplied on the commandline. Now all commandline options take exactly the same arguments as in the INI file
• Added "-accurate" command line option to choose between accurate (CPU-intensive) timing or less accurate (CPU-friendly) timing to X11 and SDL versions. This is the final version of what was considered experimental timing code in Stella 1.2
• Added "-sound" command line option to choose which sound backend to use (alsa, oss, sdl) with the X11 and SDL versions
• Added the following developer command line options to the X11 and SDL versions, which are only activated in developer builds:
  • -Dformat
  • -Dwidth
  • -Dheight
  • -Dxstart
  • -Dystart
  • -Dmerge
• Fixed window resize bug in the X11 port
• Added "-nosound" command line option to the DOS port to disable audio
• DOS port supports a "-vsync" option to synchronize emulation with the video blank of the video card
• Changed VGA code in the DOS port to use a 60Hz 320x200 and a 60Hz 320x240 graphics mode
• DOS port has been updated to run better under Windows NT, 2000, and XP. There are still issues with the sound, however, it is usable.
• DOS port is using a new Sound Blaster driver created by Matt Conte which supports auto-detection of sound cards.
• DOS port supports a STELLA_HOME environment variable that defines the location of config files.
• In the DOS port the stella.pro file is searched for first in the current working director and then in the %STELLA_HOME% directory
• In the DOS port the ROM image is searched for first using the specified path, then in %STELLA_HOME%/ROMS, and finally in %STELLA_HOME%

Features

• High speed emulation using optimized C++ code
• Supports high quality sound emulation using Ron Fries' TIA Sound Emulation library
• Emulates the Atari 2600 Joystick Controllers using your computer's keyboard or joysticks
• Emulates the Atari 2600 Keyboard Controllers using your computer's keyboard
• Emulates one Atari 2600 Paddle Controller using your computer's mouse
• Emulates four Atari 2600 Paddle Controllers using a special PC game port adaptor
• Emulates the Atari 2600 Driving Controllers using your computer's keyboard or joysticks
• Emulates the CBS Booster-Grip Controller using your computer's keyboard or joysticks
• Supports cartridges using Atari's standard 2K and 4K format
• Supports cartridges using Atari's 8K, 16K, and 32K bank-switching schemes
• Supports cartridges using Activision's 8K bank-switching scheme (Robot Tank and Decathlon)
• Supports cartridges using CBS Electronics' 12K bank-switching scheme
• Supports cartridges using Chris Wilkson's Megacart 128K bank-switching scheme
• Supports cartridges using Commavid bank-switching scheme
• Supports cartridges using M-Network's 16K bank-switching scheme
• Supports cartridges using Parker Brothers' 8K bank-switching scheme
• Supports cartridges using Tigervision's bank-switching scheme with up to 512K ROM
• Supports Supercharger single-load and multi-load games
• Supports property file for setting the properties associated with games
• Supports user specified frame rate
• Supports the NTSC and PAL television palettes
• Supports several "undocumented features" of the TIA graphics chip used by some games
• TIA emulation supports full collision checking
• DOS version of Stella works with most emulator game shells such as "Game Menu" by Jim Pragit
• DOS version of Stella supports the standard 320x200 VGA graphics mode as well as the extended 320x240 VGA graphics mode
• Linux version of Stella works with the KStella frontend by Stephen Anthony

2. What You Will Need

The following sections outline the basic system requirements for running Stella under various operating systems.

Note that for this version of Stella, you are required to have a stella.pro file. It is no longer optional as it was for past versions.

DOS

The DOS version of Stella is designed to work on an IBM-PC or 100% compatible system with the following:

• DOS 5.0 or higher
• 8 MB of RAM
• 256 color VGA graphics card
• 586/166 MHz required
• At least 2 megabytes of hard disk space available
• Sound Blaster or 100% compatible sound card required for sound
• Joysticks or gamepads are highly recommended
• Mouse and mouse driver required for paddle emulation using the mouse
• Special adaptor required for using real Atari 2600 paddles
• Emulator game shell highly recommended

Linux

The Linux version of Stella is designed to work on a Linux Workstation with the following:

• Linux Kernel 2.0.x
• X Window System
• GNU C++ compiler version 2.7.2 and the make utility are required for compiling the Stella source code; GNU C++ compiler version 2.8.1 or later is highly recommended
• 16 MB of RAM required; 32 MB highly recommended
• 8 bit color graphics card required; 16 bit color graphics card highly recommended
• 486/120 MHz required; 586/166 MHz highly recommended
• Open Sound System with a supported sound card required for sound
• Joystick device driver version 1.2.x required for joystick support
• Joysticks or gamepads are highly recommended
• Mouse required for paddle emulation using the mouse
• Special adaptor required for using real Atari 2600 paddles
• SDL version requires SDL 1.2.0 or greater

Unix

The Unix version of Stella is designed to work on a Unix Workstation with the following:

• Unix operating system
• X Window System
• GNU C++ compiler version 2.7.2 and the make utility are required; GNU C++ compiler version 2.8.1 is highly recommended
• 32 MB of RAM; 64 MB highly recommended
• 8 bit color display required; true color display highly recommended
• High performance CPU
• Open Sound System required for sound
• SDL version requires SDL 1.2.0 or greater

3. Installation

Once you have a Stella distribution you should follow the instructions for your operating system given below. If your operating system isn't listed then see the installation instructions included with the distribution for your system.

DOS

The DOS version of Stella is distributed as a ZIP archive containing the DOS executable as well as some other files. The DOS version of Stella works with DOS as well as Windows 9x. The DOS version will run under Windows NT, 2000, and XP, however, the sound may not operate correctly. You should install it as follows:

1. Change directories to the root directory:
   

      CD C:\

2. Extract the Stella distribution:

      unzip strelease.zip

3. Add the following to your AUTOEXEC.BAT file:

      SET PATH=%PATH%;C:\STELLA

4. If you have a Sound Blaster or 100% compatible sound card make sure the BLASTER environment variable is set in your AUTOEXEC.BAT file. The sound driver will attempt to auto-detect your card if the BLASTER variable isn't correctly specified. For example:

      SET BLASTER=A220 I7 D1

5. If you have a mouse make sure your mouse driver is loaded in either the CONFIG.SYS file or the AUTOEXEC.BAT file
6. Reboot your system

For the second step you'll need a program for extracting ZIP archive files. You can use PKUNZIP for DOS, the Info-Zip UnZip tool for DOS, or a number of other programs available for extracting ZIP files.

Linux

The Linux versions of Stella are distributed as a compressed tar file containing the Linux executables as well as some other files. If these pre-built executables do not seem to work on your system then download the Unix source code distribution and build your own executables. You should install the distribution as follows:

1. Extract files from the distribution:

      tar -zxvf stella-release-linux-arch.tar.gz

2. Login as root and change directories to the distribution directory
3. Copy the executable to a directory that's in your path:

      cp stella.version /usr/local/bin

4. Copy the supplied stella.pro properties file to the system-wide location:

      cp stella.pro /etc

   or to your home directory:

      mkdir ~/.stella
      cp stella.pro ~/.stella

If you have a joystick driver installed, such as joystick-1.2.13.tar.gz, you can play games using joysticks. For additional information about the Linux joystick driver see the following web site: Linux Input Drivers.

Unix

The Unix version of Stella is distributed as a compressed tar file containing the C++ source code as well as some other files. The source code can be compiled under most Unix operating systems as well as DOS. The most recent Unix code was developed with the GNU C++ compiler version 3.2, however, it should compile with other C++ compilers. The DOS port was developed with DJGPP using GNU C++ version 3.0.4. You should install the distribution as follows:

1. Extract files from the distribution:

      tar -zxvf stella-release-src.tar.gz

2. Change directories to the stella-release/src/build directory
3. Edit the makefile to meet your needs
4. Type make and follow the on screen instructions to build the preferred stella.version executable
5. Copy the executable to a directory that's in your path:

      cp stella.version /usr/local/bin

6. Copy the supplied stella.pro properties file to the system-wide location:

      cp stella.pro /etc

   or to your home directory:

      mkdir ~/.stella
      cp stella.pro ~/.stella

Currently, sound is supported using the ALSA v0.9 API (-sound alsa), the Open Sound System or OSS emulation under ALSA (-sound oss), or SDL (-sound sdl). As of this time, the X11 version cannot use SDL sound. Sound has been tested and is known to work under Linux and BSDI. For additional information on OSS or ALSA see the following web sites:

4Front Technologies (OSS)
Advanced Linux Sound Architecture (ALSA)

Support for the external sound server has been deprecated as of Stella 1.3. The sound code has been integrated into the core.

4. Games

Stella allows you to play games using ROM images of cartridges and cassettes.

Cartridges

Most games for the Atari 2600 came on cartridges. A cartridge usually consists of a single Read Only Memory (ROM) chip which contains the data and code for the game. Plugging a cartridge into the Atari 2600 allows the 2600's microprocessor to access the program stored on the cartridge.

In a similar way you must "plug" a copy of a cartridge into Stella when you want to play it. Having a ROM image, BIN file, of the cartridge allows you to do this. A ROM image is a file, which contains the actual data and code read from the cartridge. There are several ways to obtain a ROM image of a cartridge:

1. If you're handy with a soldering iron then you can design and build a device that plugs into the printer port of a PC and read the data from the cartridge
2. You can purchase the Atari 2600 Action Packs by Activision and use their ROM images
3. You can search around the internet and find ROM images to download

WARNING: It is illegal to use ROM images of games that you do not actually own since these games are still copyrighted.

Supercharger Cassettes

Supercharger games were not stored on cartridges instead they were stored on cassette tapes. The Supercharger, which plugged into the Atari 2600's cartridge slot, loaded games into its 6K of Random Access Memory (RAM) using a standard audio cassette player. The Supercharger also supported multi-loading, which allowed games to be broken into several segments and loaded at different times. This was useful for large games which had distinct parts such as role playing games.

Most of the available Supercharger ROM images are stored in 8448 bytes files. However, ROM images of multi-load games are sometimes stored in a set of 8448 byte files. The names of these files have a two character sequence number in them which indicates what load they are. The sequence starts with zero, skips a few numbers and then increments by one.

Stella supports multi-load games, however, the set of ROM images must be combined into a single ROM image file. For example to create a multi-load ROM image file for Survival Island you would do the following under Unix:

   % cat survivl0.bin survivl6.bin survivl7.bin > survivl.bin

   % copy /b survivl0.bin+survivl6.bin+survivl7.bin survivl.bin

Once you have the multi-load ROM image file, survivl.bin in this case, you can play the game using it.

5. Starting A Game

Once Stella is installed and you have some ROM images you're ready to start playing. To play a game follow the directions for your operating system.

DOS

The DOS version of Stella uses command line arguments to specify the game you'd like to play as well as other options. To see the list of available arguments, simply run stella without any options or filename. The options are provided here for reference. To run Stella use a command line of the following format:

   stella.exe [options ...] filename.bin

Options

-fps <number>

-modex

-nosound

-paddle <0|1|2|3|real>

-pro <props file>

-showinfo

-vsync

Emulator Game Shells

Instead of using the command line to run Stella you may find it easier to use an emulator game shell. An emulator game shell allows you to pick games from a menu without having to type everything at the command line. One such game shell is Jim Pragit's "Game Menu". Other frontends can be found at the Atari Age website under 2600 - Emulation.

Linux and Unix

The Unix version of Stella uses command line arguments to specify the game you'd like to play as well as other options. To see the list of available arguments, simply run stella without any options or filename. To run Stella use a command line of the following format:

   stella.version [options ...] filename.bin

Version is either x11 or sdl, depending on which version you compiled/installed.

Options (0 indicates false, 1 indicates true, others are self-explanatory)

-display <display>

-fps <number>

-owncmap <0|1>

-zoom <size>

-fullscreen <0|1>

-grabmouse <0|1>

-hidecursor <0|1>

-center <0|1>

-volume <number>

-paddle <0|1|2|3|real>

-showinfo <0|1>

-ssdir <path>

-ssname <name>

-sssingle <0|1>

-pro <props file>

-accurate <0|1>

-sound <0|alsa|oss|sdl>

-Dwidth <number>

-Dheight <number>

-Dxstart <number>

-Dystart <number>

-Dformat <NTSC|PAL>

-Dmerge <0|1>

Emulator Game Shells

There are at least three Stella frontends for Unix/Linux:

KStella, which concentrates on Stella only and includes manuals, snapshots, cartridge labels, etc.

Kemulator, which concentrates on several different emulators (Super Nintendo, Stella, MESS, etc.)

Stella Shell, which has been around the longest.

INI File

This version of Stella has support for INI files. This file can contain your default options, and eliminates the need to specify them on the command line. Any options specified on the command line will override those in the INI file.

Stella searches for an INI file in two places. First, it will look for stellarc in your $HOME/.stella directory. Then, it will look for stellarc in the /etc directory.

The syntax for the INI file is very straightforward. Any line starting with a ';' character is considered a comment and is ignored. Other lines must be of the form: command = value, where command is the same as that specified on the command line (without the '-' character), and value is dependent on the command.

For example, the following table illustrates how command line and INI entries are similar:

See the sample stellarc file for more information.

6. Keyboard Layout

The Atari 2600 console controls and controllers are mapped to the computer's keyboard as shown in the following tables:

Console Controls

Joystick Controller

Booster-Grip Controller

Driving Controller

Keypad Controller

Developer Keys

The following keys are activated only if developer support has been included:

Other Keys

The following keys are not present in all versions, so they are listed by version here:

7. Game Properties

Stella uses game properties to specify the "best" emulator settings for a game. As of Version 1.2 of Stella, there are no longer any properties built-in. You must download the latest stella.pro file from the maintainer, Erik Kovach, here.

DOS

The DOS version of Stella looks for a property file stella.pro in the current working directory. If this file isn't found then the emulator will try to guess the best settings for the game.

Linux and Unix

The Linux and Unix versions of Stella looks for the property file stella.pro in your $HOME/.stella directory. If this file is not found there, Stella will look for a stella.pro file in the /etc/ directory. If the file isn't found in either place, then the emulator wil try to guess the best settings for the game.

Property File

A property file consists of some number of blocks. Each block in the file contains the properties for a single game. For example the general format of a property file is:

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

   . . .

   ; Comments
   "Cartridge.Name"      "Value"
   "Property"            "Value"
   ""

Every block in the property file must have a unique value for the Cartridge.Name and Cartridge.MD5 properties.

Properties

Each block in a property file consists of a set of properties for a single game. Stella supports the properties described below:

8. Real Paddle Adaptor

The DOS and Linux versions of Stella support real Atari 2600 paddles using a special adaptor which connects to the PC game port. The adaptor requires the following parts:

• 1 DB15 male connector (joystick extension cable plugs into this)
• 2 DB9 male connectors (paddles plug into these)
• 4 115k resistors
• 1 Small project box
• 1 Joystick extension cable
• Some wire or ribbon cable

Most of these parts can be found at Radio Shack. I could not find a DB15 connector there or the 115k resistors, however, if you're willing to sacrifice a joystick extension cable you can do without the DB15 connector and you can always place a 100k resistor and 15k resistor in series to make a 115k resistor. A schematic of the adaptor is shown below:

As you build the adaptor be careful not to short the +5V and GND connections. Although several people have built this adaptor and use it no guarantee is given that the circuit is error free therefore USE IT AT YOUR OWN RISK!

9. Acknowledgments

Bradford W. Mott started developing Stella during the fall of 1995 and since then a number of people from around the world have contributed to the project. Some people have provided technical help while others have offered suggestions and praise. The Stella Team is grateful for all the help and support it has received over the years. The following is an incomplete list of the people who have played a part in bringing Stella to you:

10. License and Disclaimer

GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

Copyright (C) 1989, 1991 Free Software Foundation, Inc.  
59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.

Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you".

Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

• a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

• b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

• c) If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

• a) Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

• b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

• c) Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

5. You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and "any later version", you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

NO WARRANTY

11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.