Stella

## A multi-platform Atari 2600 VCS emulator

#### Release 2.6.1

## User's Guide

1. Introduction
2. What You Will Need
3. Installation
4. Games
5. Starting A Game
6. Changing Options
7. Keyboard Layout
8. Event Remapping / Input Devices
9. Viewing ROM Info
10. ROM Audit Mode
11. Stelladaptor Support
12. AtariVox/SaveKey Support
13. Integrated Debugger
14. Settings File
15. Cheatcode Manager
16. Game Properties
17. Palette Support
18. Acknowledgments
19. License and Disclaimer

February 1999 - May 2008
The Stella Team
Stella Homepage

# 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 2.6.1

- Introduced more accurate timing for NTSC vs. PAL modes, where the framerate is based on the number of scanlines per frame. This should eliminate 'clicking' sounds when emulating ROMs that don't follow the exact NTSC or PAL scanline specs.
- Added ability to see the current number of scanlines and corresponding framerate to the TIA emulation. This can be set with the '-stats' commandline argument, or dynamically turned on and off with the 'Alt-l' key combo.
- Modified '-framerate' commandline argument, where a non-zero value overrides the automatic framerate calculation (based on number of scanlines). Setting 'framerate' to zero re-enables auto-frame calculation. Also, re-enabled changing the framerate from within the UI.
- Added '-timing' commandline argument, which sets the type of waiting between processing frames. Setting it to 'sleep' emulates the previous behaviour in Stella; setting it to 'busy' emulates z26, and can in some cases eliminate screen tearing (at the expense of using all available CPU time).
- Fixed issue with debugger disassembly and mirrored $40 TIA write addresses. They were actually defined at $30, and generating incorrect labels.
- Fixed issue in AtariVox and SaveKey controllers where accessing the EEPROM sometimes failed after the first write.
- Changed AtariVox and SaveKey EEPROM emulation to default to $FF for a blank EEPROM.
- Fixed regression in cart auto-detection logic; some F6 ROMs were being misdetected as E7.
- Fixed issue with M6532/RIOT timer initialization; it was causing some ROMs to hang (most notably Summer Games). Related to this, reworked the built-in random number generator to generate 'more random' numbers.
- Fixed bug in CommandMenu where console buttons (Select, Reset, etc) weren't doing anything.

## Features

- High speed emulation using optimized C++ code
- Supports high quality sound emulation using code derived from Ron Fries' TIA Sound Emulation library, including stereo sound support
- 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 the Atari 2600 Paddle Controllers using your computer's mouse, keyboard or joysticks
- Emulates the Atari 2600 Driving Controllers using your computer's keyboard or joysticks
- Emulates the CBS BoosterGrip Controller using your computer's keyboard or joysticks
- Emulates CX-22 / CX-80 style trackballs and Amiga Mouse using your computer's mouse
- Support for real Atari 2600 controllers using the Stelladaptor
- Support for the speech portion of a real AtariVox device using a USB adaptor
- Supports EEPROM emulation for AtariVox and SaveKey controllers
- Supports almost all known bankswitching schemes (let us know if there's one we missed)
- Supports cartridge autodetection for almost all bankswitching schemes
- Supports Supercharger single-load and multi-load games
- Supports property file for setting the properties associated with games
- Supports the NTSC, PAL, PAL and SECAM television standards in 50Hz and 60Hz mode
- Supports autodetection of display format for 50Hz vs. 60Hz modes
- Supports several "undocumented features" of the TIA graphics chip used by some games
- TIA emulation supports full collision checking
- Built-in extensive debugger

# 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 not required to have a stella.pro file. ROM properties are built in, and defaults will be used whenever necessary.

## General (required for all versions of Stella)

- Enough RAM for the OS + 16MB RAM for the emulation; 32MB highly recommended
- 15 bit color minimum; 16 bit color graphics card highly recommended
- SDL version 1.2.10 or greater, latest version highly recommended
- Latest version of the zlib library
- Joysticks or gamepads are highly recommended
- Mouse or Stelladaptor with real paddles required for paddle emulation
- Some ROM images (See AtariAge for more information)

## Linux/UNIX

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

- Linux Kernel 2.4.x, Linux Kernel 2.6.x is highly recommended
- GNU C++ compiler version 2.95 and the make utility are required for compiling the Stella source code; GNU C++ compiler version 3.2.x/4.x or later is highly recommended
- i386, x86_64 or PowerPC class machine, in either 32 or 64-bit mode
- Other architectures (MIPS, PPC64, etc) have been confirmed to work as well

## Macintosh

The Mac version of Stella is designed to work on a Power Macintosh with the following:

- Mac OSX 10.2 or Above
- 500 MHz G4 PPC/Intel processor or above (Stella may work with a G3 processor, but this is still a work-in-progress)
- OpenGL capable video card. Software rendering mode is still available, but as of OSX 10.4 is substandard compared to OpenGL.

## Windows

The Windows version of Stella is designed to work on Windows 98/ME/2000/XP/Vista with the following:

- Visual C++ 7/8 or MinGW compiler is required to compile the Stella source code
- Pentium class machine required; OpenGL accelerated video card highly recommended

## Other

Stella is extremely portable, and in its lifetime has been ported to almost every platform known. It is 32/64 bit clean in Linux/Unix and Windows (Win32/Win64), and is expected to be compatible with 64-bit OSX as well. The Stella team is interested in hearing about any problems you may encounter with diverse operating systems and CPU types.

# 3. Installation

Stella is distributed in both source and binary form. Once you have a Stella distribution you should follow the instructions for your operating system given below.

If you have a supported joystick and driver installed and SDL can access the device, you can play games using joysticks.

Currently, sound is supported using SDL. As long as SDL can detect your sound card, Stella will be able to produce sound.

## Linux/UNIX

- Compressed tarball (stella-release-src.tar.gz)

1. Extract files from the distribution:

          tar zxvf stella-release-src.tar.gz

2. Change directories to the stella-release directory
3. Configure the build with the following command:

          ./configure (--help for list of options)

4. Build the executable with the following command:

          make

5. Install the executable with the following command:

          make install

- Binary DEB (stella-release-1_arch.deb)

1. Install the binary DEB with the following command:

          dpkg -i stella-release-1_arch.deb

- Binary RPM (stella-release-1.ix86.rpm)

1. Install the binary RPM with the following command:

          rpm -Uvh stella-release-1.ix86.rpm

## Macintosh

To install the Mac binary, simply download the DMG disk image. Mount the disk image, then copy the StellaOSXrelease folder to your hard drive.

## Windows

- Compressed tarball (stella-release-src.tar.gz)

1. Extract files from the distribution using Winzip, Total Commander, or some other archiving program that supports gzipped tar files
2. If compiling the Stella executable using MinGW, use the same commands as specified under Linux/UNIX - Compressed tarball
3. If compiling using Visual C++ 7:

- Open the stella-release/src/win32/Stella.sln file using Visual C++ 7
- Build the 'Stella' solution
- Copy the Stella.exe file to some directory

- Binary ZIP file (stella-release-win32.zip)

1. Unzip the binary ZIP file using Winzip or Total Commander and copy that directory somewhere

- Binary EXE installer (stella-release-win32.exe)

1. Double-click on the installer and follow the onscreen instructions

# 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

or to create it under DOS you would:

       % 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.

## Integrated GUI

As of Stella version 2.0, there is an integrated GUI for all ports. This means that using the commandline is no longer required (but commandline support is still included for those who want to use it).

If you start Stella and do not specify a ROM image, it will start in 'ROM Launcher' mode:

The ROM browser, snapshot, and external file settings may be changed by clicking the 'Options / Config Files' button:

Selecting a new path for an item is done by clicking the appropriate button(s):

You can start emulation by selecting a ROM and pressing 'Enter' or clicking 'Select', or double-clicking a ROM.

## Command Line

Stella can also be used from the commandline (assuming your operating system has a commandline). When using this mode and specifying a ROM, the ROM launcher is disabled.

To run Stella from the commandline, use the following format:

       stella [options ...] ROM_FILENAME

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

Argument | Description
--- | ---
    -video <soft|gl>
| Use SDL software or OpenGL rendering mode.
    -gl_lib <filename>
| OpenGL mode only. Specify the OpenGL library to use (only use this if you know what you're doing). For OSX, this should probably be left blank.
    -gl_filter <nearest|linear>
| OpenGL mode only. Use GL_NEAREST or GL_LINEAR filtering. GL_NEAREST results in a scaled, pixelated image, while GL_LINEAR introduces blurring.
    -gl_aspect <number>
| OpenGL mode only. Specify the amount (as a percentage) to scale the image width. Since many video modes do not use square pixels, you can reduce width until the pixels appear square. Allowable values are 50 - 100; I find 85 - 90 gives the most authentic look.
    -gl_fsmax <never|always|ui|tia>
| OpenGL mode only. Stretch fullscreen image while in the given mode.
    -gl_vsync <0|1>
| OpenGL mode only. Synchronize screen updates to the vertical blank period. This can result in smoother updates, and eliminate tearing.
    -gl_texrect <0|1>
| OpenGL mode only. Enable GL_TEXTURE_RECTANGLE extension. This causes problems for some people using ATI video cards.
    -zoom_tia <scaler>
| Use the specified zoom level while in TIA/emulation mode.
    -zoom_ui <scaler>
| Use the specified scaler while in non-emulation mode (currently, the ROM launcher and debugger).
    -fullscreen <0|1>
| Play the game in fullscreen mode.
    -fullres <WxH>
| Use this resolution in fullscreen mode.
    -center <0|1>
| Centers game window (if possible).
    -grabmouse <0|1>
| Keeps the mouse in the game window.
    -palette <standard|z26|user>
| Set the palette to either normal Stella, the one used in the z26 emulator, or a user-defined palette.
    -colorloss <1|0>
| Enable/disable the PAL color-loss effect.
    -timing <sleep|busy>
| Determines type of wait to perform between processing frames. Sleep will release the CPU as much as possible, and is the preferred method on laptops (and other low-powered devices) and when using GL VSync. Busy will emulate z26 busy-wait behaviour, and use all possible CPU time, but may eliminate graphical 'tearing'.
    -framerate <number>
| Display the given number of frames per second. Normally, Stella will determine framerate based on number of scanlines. Setting this to 0 automatically enables auto-frame calculation (ie, framerate based on scanlines).
    -sound <1|0>
| Enable or disable sound generation.
    -fragsize <number>
| Specify the sound fragment size to use. Linux/Mac seems to work with 512, Windows may need 2048 (but newer versions work with 512 as well).
    -freq <number>
| Set sound sample output frequency (0 - 48000). Default is 31400.
    -tiafreq <number>
| Set sound sample generation frequency (0 - 48000). Default is 31400.
    -volume <number>
| Set the volume (0 - 100).
    -clipvol <1|0>
| Enable volume clipping (eliminates popping).
    -cheat <code>
| Use the specified cheatcode (see Cheat section for description).
    -showinfo <0|1>
| Shows some game info while Stella is running.
    -joydeadzone <number>
| Sets the joystick deadzone area for analog joysticks. Accepts a number from 0 - 29, and uses the formula 3200 + number * 1000. So the possible deadzone values range from 3200 to 32200.
    -pspeed <number>
| Speed of digital emulation for paddles (1-15).
    -sa1 <left|right>
| Stelladaptor 1 emulates specified joystick port.
    -sa2 <left|right>
| Stelladaptor 2 emulates specified joystick port.
    -romviewer <1|0>
| Show/hide ROM info viewer in ROM launcher mode.
    -autoslot <1|0>
| Automatically switch to the next available save state slot after saving a ROM state file.
    -ssdir <path>
| The directory to save snapshot files to.
    -sssingle <0|1>
| Generate single snapshot instead of many.
    -stats <0|1>
| Show scanline and framerate info during emulation.
    -listrominfo
| Prints relevant contents of the Stella ROM database, one ROM per line, and then exit Stella. This can be used for external frontends.
    -rominfo <rom>
| Display detailed information about the given ROM, and then exit Stella.
    -launcherres <WxH>
| Set the size of the ROM launcher.
    -launcherfont <small|large>
| Set the size of the font in the ROM launcher.
    -uipalette <1|2>
| Used the specified palette for UI elements. This isn't yet complete.
    -mwheel <lines>
| Set the number of lines a mousewheel will scroll in the UI.
    -statedir <dir>
| Set the directory in which to save state files.
    -cheatfile <file>
| Set the full pathname of the cheatfile database.
    -palettefile <file>
| Set the full pathname of the user-defined palette file.
    -propsfile <file>
| Set the full pathname of the ROM properties file.
    -tiafloat <1|0>
| Set unused TIA pins to be floating on a read/peek.
    -avoxport <name>
| Set the name of the serial port where an AtariVox is connected.
    -help
| Prints a help message describing these options, and then exit Stella.

The following are useful to developers. Only use them if you know what you're doing! Note that in all cases, the values supplied to the arguments are not case sensitive.

Argument | Description
--- | ---
    -debuggerres <WxH>
| Set the size of the debugger window.
    -break <address>
| Set a breakpoint at specified address.
    -debug
| Immediately jump to debugger mode when starting Stella.
    -holdreset
| Start the emulator with the Game Reset switch held down.
    -holdselect
| Start the emulator with the Game Select switch held down.
    -holdbutton0
| Start the emulator with the left joystick button held down.
    -bs <type>
| Set "Cartridge.Type" property. See the Game Properties section for valid types.
    -type <type>
| Same as using -bs.
    -channels <Mono|Stereo>
| Set "Cartridge.Sound" property.
    -ld <A|B>
| Set "Console.LeftDifficulty" property.
    -rd <A|B>
| Set "Console.RightDifficulty" property.
    -tv <Color|BlackAndWhite>
| Set "Console.TelevisionType" property.
    -sp <Yes|No>
| Set "Console.SwapPorts" property.
    -lc <type>
| Set "Controller.Left" property. See the Game Properties section for valid types.
    -rc <type>
| Set "Controller.Right" property. See the Game Properties section for valid types.
    -bc <type>
| Sets both "Controller.Left" and "Controller.Right" properties. See the Game Properties section for valid types.
    -cp <Yes|No>
| Set "Controller.SwapPaddles" property.
    -format <format>
| Set "Display.Format" property. See the Game Properties section for valid formats.
    -ystart <number>
| Set "Display.YStart" property (0 - 64).
    -height <number>
| Set "Display.Height" property (100 - 256).
    -pp <Yes|No>
| Set "Display.Phosphor" property.
    -ppblend <number>
| Set "Display.PPBlend" property, used for phosphor effect (0-100). Default is 77.
    -hmove <Yes|No>
| Set "Emulation.HmoveBlanks" property.

# 6. Changing Options

As of version 2.0, all settings can be changed within the integrated Options GUI while Stella is running. The options are documented elsewhere in this manual and are generally self-explanatory. The Options menu can be accessed from the ROM launcher by clicking the 'Options' button, or in-game by pressing the 'Tab' key.

Options Menu dialog:

Video Settings dialog:

Audio Settings dialog:

Input Settings dialog:

This dialog is described in further detail in Section 8 - Event Remapping.

UI Settings dialog:

All UI related items can be changed here. Such items include the width and height of the ROM launcher and debugger windows, etc. Note that most of the items here require Stella to be restarted to take effect. Specific information about the ROM Info functionality is described in further detail in Section 9 - Viewing ROM Info.

Audit ROMs dialog:

This dialog is described in further detail in Section 10 - ROM Audit Mode.

Game Information dialog:

This dialog allows you to change all ROM properties as described in Section 16 - Game Properties.

Help dialog:

About dialog:

# 7. Keyboard Layout

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

As of Stella 1.4, most of these events can be remapped to other keys on your keyboard or buttons on your joystick (see Section 8 - Event Remapping). The tables below show the default settings.

Console Controls (can be remapped)

Function | Key (Standard) | Key (OSX)
--- | --- | ---
Exit emulator | Control + q | Cmd + q
Exit game mode/enter launcher mode | Escape | Escape
Enter/exit options mode | Tab | Tab
Enter/exit command mode | Backslash (\) | Backslash (\)
Enter/exit debugger | Backquote (`) | Backquote (`)
Select Game | F1 | F1
Reset Game | F2 | F2
Color TV | F3 | F3
Black/White TV | F4 | F4
Left Player Difficulty B | F5 | F5
Left Player Difficulty A | F6 | F6
Right Player Difficulty B | F7 | F7
Right Player Difficulty A | F8 | F8
Save state to current slot | F9 | F9
Change current state slot | F10 | F10
Load state from current slot | F11 | F11
Save PNG snapshot | F12 | F12
Pause/resume emulation | Pause | Pause

Joystick / BoosterGrip Controller (can be remapped)

Left Joystick (Joy0) | Right Joystick (Joy1)
--- | ---
Function | Key
--- | ---
Joystick Up | Up arrow
Joystick Down | Down arrow
Joystick Left | Left arrow
Joystick Right | Right arrow
Fire Button | Space
Trigger Button | 4
Booster Button | 5
Function | Key
--- | ---
Joystick Up | Y
Joystick Down | H
Joystick Left | G
Joystick Right | J
Fire Button | F
Trigger Button | 6
Booster Button | 7

Paddle Controller digital emulation (can be remapped independently of joystick controller)

Left Paddles | Right Paddles
--- | ---
Function | Key
--- | ---
Paddle 0 decrease | Same as 'Joy0 Left'
Paddle 0 increase | Same as 'Joy0 Right'
Paddle 0 Fire | Same as 'Joy0 Fire'
Paddle 1 decrease | Same as 'Joy0 Up'
Paddle 1 increase | Same as 'Joy0 Down'
Paddle 1 Fire | Same as 'Joy0 Booster'
Function | Key
--- | ---
Paddle 2 decrease | Same as 'Joy1 Left'
Paddle 2 increase | Same as 'Joy1 Right'
Paddle 2 Fire | Same as 'Joy1 Fire'
Paddle 3 decrease | Same as 'Joy1 Up'
Paddle 3 increase | Same as 'Joy1 Down'
Paddle 3 Fire | Same as 'Joy1 Booster'

Driving Controller (cannot be remapped, always associated with joystick controller)

Left Driving | Right Driving
--- | ---
Function | Key
--- | ---
Left Direction | Same as 'Joy0 Left'
Right Direction | Same as 'Joy0 Right'
Fire Button | Same as 'Joy0 Fire'
Function | Key
--- | ---
Left Direction | Same as 'Joy1 Left'
Right Direction | Same as 'Joy1 Right'
Fire Button | Same as 'Joy1 Fire'

Keypad Controller (can be remapped)

Left Keypad | Right Keypad
--- | ---
Pad Button | Key
--- | ---
1 | 1
2 | 2
3 | 3
4 | Q
5 | W
6 | E
7 | A
8 | S
9 | D
. | Z
0 | X
# | C
Pad Button | Key
--- | ---
1 | 8
2 | 9
3 | 0
4 | I
5 | O
6 | P
7 | K
8 | L
9 | ;
. | ,
0 | .
# | /

Developer Keys (cannot be remapped)

Function | Key (Standard) | Key (OSX)
--- | --- | ---
Set "Display.YStart" to next larger value | Alt + PageUp | Shift-Cmd + PageUp
Set "Display.YStart" to next smaller value | Alt + PageDown | Shift-Cmd + PageDown
Set "Display.Height" to next larger value | Control + PageUp | Cmd + PageUp
Set "Display.Height" to next smaller value | Control + PageDown | Cmd + PageDown

Other Keys (cannot be remapped, except those marked with '*')

Function | Key (Standard) | Key (OSX)
--- | --- | ---
Switch to next larger zoom level | Alt + = | Cmd + =
Switch to next smaller zoom level | Alt + - | Cmd + -
Toggle fullscreen/windowed mode | Alt + Enter | Cmd + Enter
Decrease volume (*) | Alt + [ | Shift-Cmd + [
Increase volume (*) | Alt + ] | Shift-Cmd + ]
Grab mouse (keep mouse in game window) | Control + g | Cmd + g
Toggle display palette (NTSC/PAL/SECAM) | Control + f | Cmd + f
Save current properties to a new properties file | Control + s | Cmd + s
Set mouse to emulate paddle 0 | Control + 0 | Cmd + 0
Set mouse to emulate paddle 1 | Control + 1 | Cmd + 1
Set mouse to emulate paddle 2 | Control + 2 | Cmd + 2
Set mouse to emulate paddle 3 | Control + 3 | Cmd + 3
Reload current ROM | Control + r | Cmd + r
Emulate 'frying' effect (*) | Backspace | Backspace
Toggle 'phosphor' effect | Alt + p | Shift-Cmd + p
Toggle palette | Control + p | Cmd + p
Toggle PAL color-loss effect | Control + l | Cmd + l
Toggle frame stats (scanline count and fps) | Alt + l | Shift-Cmd + l

# 8. Event Remapping / Input Devices

This version of Stella has event remapping. Almost every event in the emulator can be remapped to another key on the keyboard or to buttons on up to eight joysticks/gamepads (see Section 7 - Keyboard Layout for those events which can/cannot be remapped).

Note that there are currently two separate event modes in Stella; emulation mode and user-interface (UI) mode. Each mode has separate mappings, so (for example) while in emulation mode, the left arrow could mean 'joystick 0 left', while in UI mode it could mean 'move cursor left'. Emulation mode occurs whenever you're actually playing a game. UI mode occurs whenever a user interface is present (ROM launcher, debugger, settings menu, etc). Because of these different modes, there are two separate mapping areas.

To remap an event:

1. Enter options menu and click the 'Input Settings' button.
2. If you wish to remap emulation events, click the 'Emul. Events' tab. Otherwise, click the 'UI Events' tab for user interface events.
3. Select event you want to remap and click the 'Map' button.
4. Press a key or a joystick button, and that key/button will be bound to the selected event. If nothing seems to happen, either Stella can't see the input device, or the selected event doesn't support being remapped to the input device.
5. Erase a mapping by clicking 'Erase', or cancel a remap in progress by clicking 'Cancel'.
6. Reset default mappings by clicking 'Defaults'.

The following screenshots illustrate the event remapping process:

Virtual devices can be configured under the 'Virtual Devs' tab, shown below:

Stelladaptor devices can be configured to either the left or right virtual ports. See Section 11 - Stelladaptor Support for further information.

Joystick deadzone area for analog joysticks can be set here. The deadzone can be adjusted in an interval from 0 - 29, which internally is converted to the range 3200 - 32200 using the formula '3200 + DEADZONE * 1000'.

Paddle settings are also configured here. The mouse can emulate either paddle 0, 1, 2, or 3. Note that some paddle games don't default to paddle 0. In those cases, the ROM properties will automatically set the mouse to emulate the paddle used by Player 0. So, for example, a ROM that defaults to paddle 1 (Demons to Diamonds) will set 'Mouse is paddle' to 1, and a ROM that defaults to paddle 3 (Tac-Scan) will set 'Mouse is paddle' to 3.

Paddle speed is used when emulating a paddle using a digital device (keyboard, digital joystick, etc). Because of the on/off nature of digital devices, there are no smooth analog values as would be present on a real paddle. When using digital devices, the paddle is moved a certain amount each frame. This speed setting specifies how much movement will occur.

The serial port to which a real AtariVox is connected can be set here. See Section 12 - AtariVox/SaveKey Support for further information.

# 9. Viewing ROM Info

Stella supports viewing snapshots and ROM properties of the currently selected ROM in the ROM launcher. Support is automatic, as long as your snapshot directory contains snapshots in the appropriate format. An archive of updated snapshots will be available on the Stella webpage. This archive may be updated periodically as new ROMs are found, and also for each new release of Stella.

Currently, there are several restrictions for this feature:

1. Only 1x snapshots are supported (maximum size of 320x260). This means that if you generate your own snapshots, you'll have to switch to 1x zoom mode first before you save them.
2. The ROM launcher window must be sized at least 640x480.
3. The size of the ROM info viewer is tied to the current zoom level of the user interface. So, for example, if you wish to see snapshots in 2x mode, the minimum screen size to do so is 1280x960 (double the size of the minimum 640x480).

Number three in particular is a problem for users with screenmodes smaller than 1280x960. Such users will only be able to view snapshots (and as a result the entire UI) in 1x mode. The problem is, in 1x mode, the ROM launcher font is usually illegibly small. Therefore, there's now support for changing the size of the ROM launcher font to compensate for this.

Note that most of these restrictions will be fixed in a future release, when the UI becomes completely font-sensitive and configurable, and the size of the ROM Info viewer will be configurable separately from the UI zoom level. To illustrate, the following snapshots show the ROM launcher in 1x and 2x mode:

ROM Launcher in 1x mode, UI sized 800x480, small launcher font:

ROM Launcher in 1x mode, UI sized 1020x700, large launcher font:

ROM Launcher in 2x mode, UI sized 700x480(*2), small launcher font:

# 10. ROM Audit Mode

Stella has the ability to rename all your ROMs according to the name specified in the properties database. This is useful if you've downloaded ROMs in DOS 8.3 naming format, and wish the filenames to be more descriptive, or the current filenames are too large to see in the launcher.

This feature is accessible from Options -> Audit ROMs, and is only available while in ROM launcher mode. The dialog box for this feature is as follows:

Simply select the ROM path with the 'Audit path' button, and click the 'Audit' button. The ROMs will then be renamed according to their internal properties. When the operation is complete, the number of ROMs that were renamed (as well as ones that weren't) will be shown.

There are several items to take note of:

- THIS OPERATION CANNOT BE UNDONE. I cannot stress this enough; if you aren't completely sure you want to rename your ROMs, don't use this function. There is no undo feature, and one won't be added.
- Only filenames that Stella considers to be valid ROMs will be considered. Currently, this means files that end in '.bin', '.rom', '.a26', '.zip' and '.gz'. Files which don't have these extensions will be ignored.
- If a valid ROM doesn't have a properties entry, it will be ignored.

# 11. Stelladaptor Support

Stella supports real Atari 2600 joysticks, paddles and driving controllers using the Stelladaptor device.

Stella can use up to two Stelladaptors; any extra ones are ignored. Stelladaptor devices will be automatically detected and configured. Devices can be plugged/unplugged while the emulation is running; Stella will detect the change and act accordingly.

The detection and configuration is as follows:

- The first Stelladaptor found will act as the left game port on a real Atari. Depending on the device, Stella will detect it as either the left joystick, paddles 0 & 1, or the left driving controller.
- The second Stelladaptor found will act as the right game port on a real Atari. Depending on the device, Stella will detect it as either the right joystick, paddles 2 & 3, or the right driving controller.
- Any other Stelladaptors will be ignored.
- The assignment ordering of Stelladaptor to port can be redefined with 'sa1' and 'sa2' (see description in 'Starting a Game').

# 12. AtariVox/SaveKey Support

Stella supports a real AtariVox device for the speech/SpeakJet portion of the controller. You will need a real AtariVox device, located here, as well as some means of connecting it to your computer (some sort of serial port/USB adaptor). There should be drivers for your serial convertor, which allow your particular operating system to 'see' the device. Configuring this is outside the scope of this document. Once your operating system properly detects the AtariVox, you will need to tell Stella which serial port it is connected to. This is done by using the '-avoxport' commandline argument, or by setting it in the UI under the 'Virtual Devs' tab in 'Input Settings', as described in Section 8.

Note that you must use the entire name of the port as specified by your operating system. For example, in Windows this would be COM1, COM2, etc; Linux and OSX tend to use '/dev/xxxxxx'. For now, only Linux/UNIX, OSX, and Win32 are supported.

Support for the EEPROM portion of the AtariVox and SaveKey is currently emulated. That is, a file will be created on your computer simulating the EEPROM; the actual EEPROM hardware itself will not be used or modified. This is very useful in the testing stages of creating a new game, since writing to a real EEPROM many times will eventually wear it out.

The EEPROM files have a special name/location depending on which version of Stella you use, which are currently not configurable:

Linux/Unix | $HOME/.stella/atarivox_eeprom.dat $HOME/.stella/savekey_eeprom.dat
Macintosh | $HOME/.stella/atarivox_eeprom.dat $HOME/.stella/savekey_eeprom.dat
Windows | %MY_DOCUMENTS%\Stella\atarivox_eeprom.dat %MY_DOCUMENTS%\Stella\savekey_eeprom.dat OR %CURRENT_DIR%\atarivox_eeprom.dat %CURRENT_DIR%\savekey_eeprom.dat (if a file named 'disable_profiles.txt' exists in the application directory)

Note that these EEPROM files will be created when necessary, and initialized as a real EEPROM would be (containing all $FF). The files can be manually deleted, which is very useful in testing cases where a ROM is accessing the EEPROM for the first time.

# 13. Integrated Debugger

Have a look at this page for integrated debugger documentation.

# 14. Settings File

Stella will remember when you change a setting either at the command line or while the emulation is running, and use the settings the next time you start the emulator. The settings are saved in a text file which can be edited outside of Stella. 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 settings file.

The syntax for the settings 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 settings entries are similar:

Command Line | Settings File
--- | ---
-video gl | video = gl
-volume 75 | volume = 75
-showinfo 1 | showinfo = 1 (or showinfo = true)

The settings file has a special name/location depending on which version of Stella you use, which is currently not configurable:

Linux/Unix | $HOME/.stella/stellarc
Macintosh | Not applicable; settings are saved in $HOME/Library/Preferences/StellaOSX.plist
Windows | %MY_DOCUMENTS%\Stella\stella.ini OR %CURRENT_DIR%\stella.ini (if a file named 'disable_profiles.txt' exists in the application directory)

# 15. Cheatcode Manager

Stella 2.0 contains support for Bob Colbert's Cheetah cheat codes, as well as an extended Stella-specific type of cheat code that works on bankswitched ROMs.

To add/remove/edit a cheat code, enter the 'Cheat Code' dialog:

Currently, there are three types of cheatcodes available, all of which must be entered in hexidecimal format:

- Per-frame RAM cheats:
  Evaluated each frame, and apply to RAM only. Format as follows:

         4-digit code: c041
         c0 = address
         41 = data

- Cheetah codes, which are explained in detail on Bob Colbert's web page, along with a list of codes for various games. Cheetah codes don't support bankswitched ROMs, so they only work for 2K or 4K ROMs. Format as follows:

         6-digit (cheetah) code: aaaddc
         aaa = address - $f000
         dd = data
         c = count - 1

- Stella extended cheats are similar to Cheetah codes, except that they can be 7 or 8 digits long, with the extra digits used for the bank number:

         7-digit (stella) code: baaaddc
         b = bank (0 to $f)
         aaa = address - $f000
         dd = data
         c = count - 1

         8-digit (stella) code: bbaaaddc
         bb = bank (0 to $ff)
         aaa = address - $f000
         dd = data
         c = count - 1

There's also the concept of one shot codes. These codes work exactly the same as above, except they aren't saved. They are evaluated once and immediately discarded.

Here are a few cheat codes we've found:

    Pitfall (standard Cheetah codes):
       5b0ea1 - infinite lives
       723ea1 - infinite time
       aa5??0 - set starting level, ?? = 01 to ff (d0 is kinda neat)

    Battlezone (Stella extended codes):
       1236ea1 - infinite lives

    Ms Pac-Man (Stella extended codes):
       108fea1 - infinite lives

The name of the cheat database file is configurable through the '-cheatfile' commandline argument and within the application itself (see Section 5 - Starting a Game). If the path for this file hasn't been set, the default filename will depend on the version of Stella, as follows:

Linux/Unix | $HOME/.stella/stella.cht
Macintosh | $HOME/.stella/stella.cht
Windows | %MY_DOCUMENTS%\Stella\stella.cht OR %CURRENT_DIR%\stella.cht (if a file named 'disable_profiles.txt' exists in the application directory)

Stella will require a restart for changes to this file to take effect.

# 16. Game Properties

Stella uses game properties to specify the "best" emulator settings for a game. As of version 2.2 of Stella, a default database of properties are built-in, but you may modify these through the use of a stella.pro file. This per-user file will contain all properties modified by the user. So this means that when you upgrade Stella, your personal properties settings are preserved.

## 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.MD5"      "Value"
       "Property"           "Value"
       ""

       ; Comments
       "Cartridge.MD5"      "Value"
       "Property"           "Value"
       ""

       . . .

       ; Comments
       "Cartridge.MD5"      "Value"
       "Property"           "Value"
       ""

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

## Properties

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

Cartridge.MD5: | Indicates the MD5 checksum of the ROM image as a string of hexadecimal digits. Stella uses this property while attempting to match a game with its block of properties. If the value of the property matches the MD5 checksum of the ROM image then Stella uses that block of properties for the game. You can use the GNU md5sum program, which is included with most Linux distributions, to calculate the MD5 checksum of a ROM image.
Cartridge.Manufacturer: | Indicates the game's manufacturer.
Cartridge.ModelNo: | Indicates the manufacturer's model number for the game.
Cartridge.Name: | Indicates the actual name of the game.
Cartridge.Note: | Contains any special notes about playing the game.
Cartridge.Rarity: | Indicates how rare a cartridge is, based on the scale described on AtariAge.
Cartridge.Sound: | Indicates if the game should use 1 or 2 channels for sound output. All original Atari 2600 machines supported 1 channel only, but some homebrew games have been written to take advantage of stereo sound. The value must be Mono or Stereo.
Cartridge.Type: | Indicates the bank-switching type for the game. The value of this property must be either Auto-detect or one of the following (for more information about bank-switching see Kevin Horton's 2600 bankswitching document or the documentation in each cartridges source code file). Types marked as (*) do not currently have reliable auto-detection, or may not be fully supported in the debugger:
Type | Description
--- | ---
0840 (*) | 8K ECONObanking
2K | 2K Atari
3E | 32K Tigervision
3F | 512K Tigervision
4A50 (*) | 64K 4A50 + ram
4K | 4K Atari
AR | Supercharger
CV | Commavid extra ram
DPC | Pitfall II
E0 | 8K Parker Bros
E7 | 16K M-network
F4 | 32K Atari
F4SC | 32K Atari + ram
F6 | 16K Atari
F6SC | 16K Atari + ram
F8 | 8K Atari
F8SC | 8K Atari + ram
FASC | CBS RAM Plus
FE | 8K Decathlon
MB | Dynacom Megaboy
MC | C. Wilkson Megacart
SB (*) | 128-256k SUPERbanking
UA | 8K UA Ltd.
X07 (*) | 64K AtariAge
Console.LeftDifficulty: | Indicates the default difficulty setting for the left player. The value must be A or B.
Console.RightDifficulty: | Indicates the default difficulty setting for the right player. The value must be A or B.
Console.TelevisionType: | Indicates the default television setting for the game. The value must be Color or BlankAndWhite.
Console.SwapPorts: | Indicates that the left and right ports should be swapped internally. This is used for ROMs like 'Raiders' where the Player 0 joystick is plugged into the right joystick port. The value must be Yes or No.
Controller.Left: | Indicates what type of controller the left player uses. The value must be BoosterGrip, Driving, Keyboard, Paddles, Trackball22, Trackball80, AmigaMouse or Joystick.
Controller.Right: | Indicates what type of controller the right player uses. The value must be BoosterGrip, Driving, Keyboard, Paddles, Trackball22, Trackball80, AmigaMouse, AtariVox, SaveKey or Joystick.
Controller.SwapPaddles: | Indicates that the left and right paddles in a particular port should be swapped. This is used for ROMs like 'Demons to Diamonds' where the default paddle is paddle 1, not paddle 0. Other ROMs such as 'Tac-Scan' default to paddle 3, which can be set using both 'Controller.SwapPaddles' and 'Console.SwapPorts'. The value must be Yes or No.
Display.Format: | Indicates the television format the game was designed for. The value must be Auto-detect, NTSC, PAL, SECAM, NTSC50, PAL60 or SECAM60.
Display.YStart: | Indicates the scan-line to start displaying at. The value must be n such that 0 <= n <= 64.
Display.Height: | Indicates the number of scan-lines to display. The value must be n such that 100 <= n <= 256.
Display.Phosphor: | Indicates whether the phosphor effect should be emulated or not. The value must be Yes or No.
Display.PPBlend: | Indicates the amount of blending which will occur while using the phosphor effect. The value must be n such that 0 <= n <= 100. The default value is 77.
Emulation.HmoveBlanks: (*) | Indicates whether the TIA HMOVE blank bug should be emulated or not. The value must be Yes or No.

Note: Items marked as '*' are deprecated, and will probably be removed in a future release.

The name of the properties file is configurable through the '-propsfile' commandline argument and within the application itself (see Section 5 - Starting a Game). If the path for this file hasn't been set, the default filename will depend on the version of Stella, as follows:

Linux/Unix | $HOME/.stella/stella.pro
Macintosh | $HOME/.stella/stella.pro
Windows | %MY_DOCUMENTS%\Stella\stella.pro OR %CURRENT_DIR%\stella.pro (if a file named 'disable_profiles.txt' exists in the application directory)

Stella will require a restart for changes to this file to take effect.

# 17. Palette Support

An Atari 2600 palette consists of 128 colours, which are different for the three major television standards (NTSC, PAL, SECAM). Stella supports two built-in palettes and one user-defined palette for each format. These are set using the '-palette' option, and are described as follows:

standard | The default palette from Stella 1.4 onwards.
z26 | The palette from the z26 emulator.
user | An external palette file, supplied by the user.

Support for a user-defined palette is a new feature for Stella 2.3, and is further described as follows:

- The palette file must be at least 792 bytes long. Colours are stored in 24-bit RGB, with the first byte for red, the second for green, the third for blue, for a total of 3 bytes per colour.
- The first 384 bytes of the file (128 * 3) will be used for the NTSC palette. The next 384 bytes (128 * 3) will be for the PAL palette. The next 24 bytes (8 * 3) will be for the SECAM palette, which consists of eight distinct colours. Any extra data in the file will be ignored.
- The PAL colour-loss effect is calculated within Stella. You do not need to specify those colours in the palette file.

The name of the palette file is configurable through the '-palettefile' commandline argument and within the application itself (see Section 5 - Starting a Game). If the path for this file hasn't been set, the default filename will depend on the version of Stella, as follows:

Linux/Unix | $HOME/.stella/stella.pal
Macintosh | $HOME/.stella/stella.pal
Windows | %MY_DOCUMENTS%\Stella\stella.pal OR %CURRENT_DIR%\stella.pal (if a file named 'disable_profiles.txt' exists in the application directory)

Note that to actually use the external palette, the palette file must exist and be valid, and the palette option should be set to user. The current ROM will have to be reloaded for changes to this file to take effect.

# 18. 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:

Stephen Anthony | Ported Stella 1.1 to SDL. Added extra command line options to X11/SDL versions. Added INI file support, faster startup, snapshot support, and pause functionality to core. Converted Stella 1.1 manual to HTML. Ported codebase to SDL for Windows/MacOSX. Added OpenGL support and Stelladaptor support. Current maintainer for the Linux and Windows versions.
David Aspell | Ported release 0.7 of Stella to Java
Christopher Bennett | Helped discover a Superchanger emulation bug in release 1.0 of Stella
Alexander Bilstein | Provided "A Brief History of the Atari 2600" for this manual
Dan Boris | Provided technical information on the Supercharger
Piero Cavina | Allowed "Oystron" to be included in the Stella distribution
Bob Colbert | Allowed "Okie Dokie" to be included in the Stella distribution
Joe D'Andrea | Author of the IRIX port of Stella until release 1.2
Renato Ferreira | Provided code to support private colormaps under Unix
Ron Fries | Author of the awesome TIA Sound library
Aaron Giles | Author of the Power Macintosh version of Stella until release 1.1
Mark Grebe | Author of the Macintosh OSX version of Stella starting with the 1.4 release. Helped with Stelladaptor support.
Alex Herbert | Provided much information on AtariVox and SaveKey functionality
Richard Hutchinson | Provided an AtariVox USB adaptor to help with AVox development
Mark Hahn | Allowed "Elk Attack" to be included in the Stella distribution and provided help with the TIA HMOVE blank bug
Kevin Horton | Author of the definitive Atari 2600 bank-switching document
Thomas Jentzsch | Provided updated NTSC palette and many ideas
Kostas Nakos | Author/maintainer of the WinCE version of Stella starting with the 2.0 release
Erik Kovach | Author of the property file for release 0.7, 1.0, 1.1, and 1.2 of Stella
Daniel Marks | Provided improved keyboard joystick support for Stella release 0.1
James Mcclain | Provided patches for the 1.2 release to get Stella to compile with GCC 3.0
David McEwen | Author of the Acorn version of Stella
Jeff Miller | Author of the Windows version of Stella until release 1.2
Dan Mowczan | Provided a Supercharger to help with Stella's development
Jack Nutting | Author of the OpenStep version of Stella
John Payson | Provided EEPROM emulation code for AtariVox and SaveKey support
Manuel Polik | Author of the Windows version of Stella starting with the 1.2 release
Jim Pragit | Author of the "Game Menu" emulator game shell
John Saeger | Participated in a helpful discussion on understanding the TIA's RESPx multi-sprite trick
Chris Salomon | Provided information and code to help implement Supercharger support
Glenn Saunders | Provided a Supercharger to help with Stella's development
Jason Scott | Organizer of the property file archive for early versions of Stella; now he's helping with the web site
David Shaw | Provided make targets for the BSDI platform
Raul Silva | Helped with design and graphics for an early version of the Stella web site
Chris Snell | Maintained a mirror of the Stella FTP site
Darrell Spice Jr. | Author of the OS/2 version of Stella
John Stiles | Maintained the Macintosh version of Stella until release 1.2
Eckhard Stolberg | Provided a description of the TIA bug that produces the star field effect in Cosmic Ark, provided the PAL television palette, and participated in a helpful discussion on understanding the TIA's RESPx multi-sprite trick. Provided the Commavid, Megaboy, 4A50 and X07 support for Stella as well as some improved Supercharger BIOS code.
Matthew Stroup | Author of the Amiga version of Stella
Joel Sutton | Author of the FreeBSD version of Stella
Greg Troutman | Allowed "This Planet Sucks" to be included in the Stella distribution
Curt Vendel | Provided schematics of the TIA which are being used to improve the TIA emulation.
David Voswinkel | Maintainer of the PSP version of Stella starting with the 2.0 release
Brian Watson | Helped with getting the illegal CPU instruction support working with Stella. Brian also submitted a number of other changes, such as debugger support, which have been finally integrated into the 2.0 release of Stella. Without a doubt, there would be no debugger support in Stella if not for the tireless work of Brian.
Keith Wilkins | Maintained the DOS version of Stella until release 0.7
Jeff Wisnia | Provided technical data sheet for the 6532 RIOT chip
Albert Yarusso (aka Al from AtariAge) | Provided helpful feedback for the OSX port, and generously donated an AtariVox device to help with development
Alex Zaballa | Maintainer of the GP2X version of Stella starting with the 2.1 release

# 19. 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.)

These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

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.)

The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

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.