Contents

• A Brief History of the Atari 2600
• Introduction
  
  • Features
• Getting Started
  
  • Requirements
  • Installation
  • Locating Game Images (aka ROMs)
  • Playing a Game
  • Keyboard Layout
  • Hotkeys
  • Controller Map
  • Stella's 'Time Machine'
• Advanced Configuration
  
  • Using the Command Line
  • Changing Options
  • Event Remapping/Input Devices
  • ROM Launcher
  • ROM Launcher Viewer
  • ROM Launcher Context Menu
  • ROM Audit Mode
  • Stelladaptor/2600-daptor Support
  • AtariVox/SaveKey Support
  • Developer Options/Integrated Debugger
  • Settings File
  • Cheatcode Manager
  • Viewing the System Log
  • Game Properties
  • Palette Support
• Acknowledgments
• 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

Introduction

Stella is a freely distributed multi-platform Atari 2600 VCS emulator; originally developed for Linux by Bradford W. Mott, it is now maintained by Stephen Anthony. 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, Unix, and Windows, as well as consoles such as Sega Dreamcast, GP2X, Nintendo DS and Playstation Portable (among others).

Features

• High speed emulation using optimized C++14 code
• Supports high quality TIA emulation using the cycle-exact TIA core from 6502.ts by Christian Speckner
• Supports high quality sound emulation using code derived from Chris Brenner's Atari 2600 FPGA project, including cycle-exact audio, analog interference from mixing of audio channels, as well as stereo sound support; dynamic sound resampling is also included
• Emulates the Atari 2600 Joystick Controllers using your computer's keyboard, joysticks or mouse
• 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, joysticks or mouse
• Emulates the CBS BoosterGrip Controller using your computer's keyboard, joysticks or mouse
• Emulates the Sega Genesis Controller using your computer's keyboard, joysticks or mouse
• Emulates CX22/CX80 style trackballs and Amiga/Atari Mouse using your computer's mouse
• Emulates Spectravideo CompuMate system using your computer's keyboard, including mapping of CompuMate 'Backspace', 'Space' and 'Enter' functionality to to the actual keys on your keyboard
• Emulates the Mindlink Controller and the Light Gun using your computer's mouse
• Supports autodetection for most common controller types
• Support for real Atari 2600 controllers using the Stelladaptor and 2600-daptor/2600-daptor II
• Support for the speech portion of a real AtariVox device connected to your PC using a USB adaptor
• Supports EEPROM emulation for AtariVox and SaveKey controllers, as well as FLASH support in various cartridge schemes
• Supports all known bankswitching schemes (let us know if there's one we missed)
• Supports DPC+/CDF(J) bankswitching schemes from the Harmony Cart, including partial emulation of the ARM processor
• Supports cartridge autodetection for almost all bankswitching schemes
• Supports using ROM filename extensions to force specific bankswitching schemes
• Supports using ROM filename to force specific display formats
• Supports Supercharger single-load and multi-load games
• Supports the usual raw A26/BIN/ROM formats, also when stored in ZIP files
• Supports property file for setting the properties associated with games
• Supports the NTSC, PAL and SECAM television standards in 50Hz and 60Hz mode
• Supports autodetection of display format for 50Hz vs. 60Hz modes
• Supports most "undocumented features" of the TIA graphics chip used by some games
• TIA emulation supports full collision checking, with ability to disable TIA sprites and collisions for each object separately
• Full system state save/load functionality
• Automatic save state creation ('Time Machine') which allows moving back and forth in the recorded timeline
• Cross-platform UI including a built-in ROM launcher frontend
• Built-in extensive debugger, including static analysis with the Distella disassembler and dynamic analysis at runtime by tracking code/graphics/data sections, and generation of DASM-compatible disassembly files
• Emulation of CRT TV systems using Blargg filtering, including presets for several common TV outputs (Composite, S-Video, RGB, etc.), and ability to fully customize many attributes (contrast, brightness, saturation, gamma, etc.).
• Built-in ROM database with information partially compiled by RomHunter

Getting Started

Requirements

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

General (required for all versions of Stella)

• SDL version 2.0.3 or greater, latest version highly recommended
• 15/16 bit color minimum; 24/32 bit color graphics card highly recommended
• Enough RAM for the OS + 256MB RAM for the emulation; 512MB+ highly recommended
• Joysticks or gamepads are highly recommended
• Mouse or Stelladaptor/2600-daptor 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:

• i386 or x86_64 class machine, with 32 or 64-bit distribution
• OpenGL capable video card
• Other architectures (MIPS, PPC, PPC64, etc.) have been confirmed to work, but aren't as well tested as i386/x86_64
• GNU g++ v/6 or Clang v/3.9 (with C++14 support) and the make utility are required for compiling the Stella source code

Macintosh

The Mac version of Stella is designed to work on an Apple Macintosh with the following:

• macOS 10.7 or above
• 64-bit Intel processor
• OpenGL capable video card
• Xcode 8.0 is required to compile the Stella source code

Windows

The Windows version of Stella is designed to work on Windows Vista/7/8/10 with the following:

• Direct3D or OpenGL capable video card
• Visual C++ 2017/2019 Community is required to compile the Stella source code

Other

Stella is extremely portable, and in its lifetime has been ported to almost every platform where the SDL library exists. It is 32/64-bit and endian clean in Linux/Unix, macOS and Windows. The Stella Team is interested in hearing about any problems you may encounter with diverse operating systems and CPU types.

Installation

Stella is distributed in both source and binary form. In general, you should always download and install the appropriate binary version. Compiling from source is only recommended for developers, or if the binary version doesn't work for some reason. Once you have a Stella distribution you should follow the instructions for your operating system given below.

Linux/UNIX

• Binary DEB (stella-release-1_arch.deb)
  • Install the binary DEB with the following command:

       dpkg -i stella-release-1_arch.deb

• Binary RPM (stella-release-1.arch.rpm)
  • Install the binary RPM with the following command:

       rpm -Uvh stella-release-1.arch.rpm

• Building and installing from source code
  • See the developers build instructions at the Stella Development Page.

Macintosh

• Binary DMG file (Stella-release-macos.dmg)
  • Double-click the disk image, open the 'Stella' folder, then copy the Stella.app package to your 'Applications' folder.


• Building and installing from source code
  • See the developers build instructions at the Stella Development Page.

Windows

• Binary EXE installer (stella-release-arch.exe)
  1. Double-click on the installer and follow the onscreen instructions


• Binary ZIP file (stella-release-windows.zip)
  1. Unzip the binary ZIP file using Winzip or Total Commander
  2. Copy the contents of either 32-bit or 64-bit directory somewhere on your system


• Building and installing from source code
  • See the developers build instructions at the Stella Development Page.

Locating Game Images (aka ROMs)

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:

• Search around the internet and find ROM images to download (websites such as AtariAge and AtariMania/RomHunter may be useful). Many homebrewers make their ROMs available too.
• You can purchase the Atari 2600 Action Packs by Activision and use their ROM images
• If you're handy with a soldering iron then you can design and build a device that plugs into a PC and read the data from the cartridge

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

Supported File formats

Stella supports ROMs ending with extensions .a26, .bin, .rom, and .zip. For the ZIP archive format, Stella will look into the archive and if it contains only one ROM image file, Stella will automatically load it. If an archive contains many such files, Stella will display a virtual filesystem with the contents of the archive. This can be then browsed like a normal directory.

Other extensions are also possible, namely to force a specific bankswitch scheme. Normally, the bankswitching scheme for a ROM is determined automatically, or manually by setting a ROM property, and you never have to do anything yourself. However, it is also possible to force the bankswitch type to use by adding a special filename extension. These extensions are listed in the ROM properties section under Cart.Type -> File Extension.

Note: These extensions are the same as those used by the Harmony Cart and Unocart and are not case-sensitive, so you can name your files and have them work across all applications. Again, to be clear, this is only necessary when you want to override the default bankswitching scheme for a ROM. This will not normally be necessary.

Playing a Game

Once Stella is installed and you have some ROM images you're almost ready to start playing.

Integrated GUI

Stella contains an integrated GUI for all ports. Commandline support is also available 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:

If this is your first time starting Stella, you may have to navigate to your ROMs. The path of the first ROM you play automatically defines the default ROM path. You can change it later in the ROM Launcher dialog.

At this point, you may want to set the locations for snapshots. This is described in more detail in Advanced Configuration - Snapshot Settings. These settings are optional, and can be left at the defaults if you won't be using snapshots in the ROM launcher.

You can start emulation by selecting a ROM and pressing 'Enter' or clicking 'Select', or double-clicking a ROM. Note that some games require you to 'Reset' the console before you start playing. In this case, you need to hit the virtual reset switch, which by default is the F2 key. Also, some games may require that you press the joystick fire button to begin, which by default is the Left Control or Space key(s), or button 0 on your joystick. If a game uses a more complex controller, see Getting Started - Keyboard Layout for more information. To exit a game and re-enter the ROM launcher, press the 'Escape' key.

Using the 'Search' textbox in the upper-right of the ROM launcher, the listing can be narrowed down, showing only the ROMs that match the pattern you enter.

While the file listing is in focus, you can type some characters, and the listing will 'jump' to the file that matches what you typed. This is case-insensitive. Hold down the Shift key on the first character to select directories instead. The delay between successive keypresses being treated as part of one word is controlled by the 'listdelay' option; see User Interface Settings to change this setting.

Command Menu

While playing a game, normally one would use the keyboard shortcuts for controlling the 'virtual' switches in Stella (ie, the commands associated with the function keys as described in Getting Started - Keyboard Layout). However, another alternative is available. Pressing the '\' key toggles a command menu dialog as follows:

This dialog contains a set of buttons that represent the same functionality as the function keys and display the current state. You may find this useful if you cannot remember all the function key events, or you wish to use Stella without a keyboard (ie, in a standalone gaming system).

Keyboard Layout

The Atari 2600 console controls and controllers are mapped to the computer's keyboard as shown in the following tables. However, most of these events can be remapped to other keys on your keyboard or buttons on your joystick (see Advanced Configuration - Event Remapping). The tables below show the default settings.

Note: All key names are based on the US QWERTY keyboard layout.. If you use a different layout some keys may differ. You can use the following layout image as reference where to find the US keys on your keyboard.

Hotkeys

Console Controls (can be remapped)

Function	Key (Standard)	Key (macOS)
Exit emulator	Control + q	Cmd + q
Exit game mode/enter launcher mode	Escape	Escape
Enter/exit options mode	Tab/Escape	Tab/Escape
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 A	F5	F5
Left Player Difficulty B	F6	F6
Right Player Difficulty A	F7	F7
Right Player Difficulty B	F8	F8
Save state to current slot	F9	F9
Save all Time Machine states	Alt + F9	Cmd + F9
Change to previous state slot	Shift + F10	Shift + F10
Change to next state slot	F10	F10
Automatically change state slot	Alt + F10	Cmd + F10
Load state from current slot	F11	F11
Load all states into Time Machine	Alt + F11	Cmd + F11
Save PNG snapshot	F12	F12
Pause/resume emulation	Pause	Shift-Cmd + p

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 Left Control, Space Top Booster Button 4 Handle Grip Trigger 5	Function Key Joystick Up Y Joystick Down H Joystick Left G Joystick Right J Fire Button F Top Booster Button 6 Handle Grip Trigger 7

Sega Genesis Controller (cannot be remapped, always associated with joystick and booster-grip controllers)

Left Pad	Right Pad
Function Key Pad Up Same as 'Joy0 Up' Pad Down Same as 'Joy0 Down' Pad Left Same as 'Joy0 Left' Pad Right Same as 'Joy0 Right' Button 'B' Same as 'Joy0 Fire' Button 'C' Same as 'Joy0 Top Booster Button'	Function Key Pad Up Same as 'Joy1 Up' Pad Down Same as 'Joy1 Down' Pad Left Same as 'Joy1 Left' Pad Right Same as 'Joy1 Right' Button 'B' Same as 'Joy1 Fire' Button 'C' Same as 'Joy1 Top Booster Button'

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'

Trackball Controller (uses mouse, left port only)

Left Trackball
Function Key Fire Button Same as 'Joy0 Fire'

Light Gun Controller (uses mouse, left port only)

Left Light Gun
Function Key Fire Button Same as 'Joy0 Fire'

Paddle Controller digital emulation (can be remapped)

Left Paddles	Right Paddles
Function Key Paddle 0 Turn Left Left arrow Paddle 0 Turn Right Right arrow Paddle 0 Fire Left Control, Space Paddle 1 Turn Left Up arrow Paddle 1 Turn Right Down arrow Paddle 1 Fire 4	Function Key Paddle 2 Turn Left G Paddle 2 Turn Right J Paddle 2 Fire F Paddle 3 Turn Left Y Paddle 3 Turn Right H Paddle 3 Fire 6

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 . # /

CompuMate Controller (cannot be remapped)

CompuMate	Key
0 - 9	0 - 9
A - Z	A - Z
Comma	Comma
Period	Period
Func	Control (left or right)
Shift	Shift (left or right)
Enter	Return/Enter
Space	Space
Func-Space	Shift + Backspace
+	+ or Shift + 1
-	- or Shift + 2
*	Shift + 3
/	/ or Shift + 4
=	= or Shift + 5
?	? (Shift + /) or Shift + 6
$	Shift + 7
[	[ or Shift + 8
]	] or Shift + 9
"	" (Shift + ') or Shift + 0

Audio & Video Keys (can be remapped)

Function	Key (Standard)	Key (macOS)
Toggle sound	Control + ]	Control + ]
Decrease volume	Alt + [	Cmd + [
Increase volume	Alt + ]	Cmd + ]
Switch to next larger zoom level in windowed mode, toggle stretching in fullscreen mode	Alt + =	Cmd + =
Switch to next smaller zoom level in windowed mode, toggle stretching in fullscreen mode	Alt + -	Cmd + -
Toggle windowed/fullscreen mode	Alt + Enter	Cmd + Enter
Toggle adapting display refresh rate to game frame rate Note: Not available for macOS.	Alt + r	Cmd + r
Decrease overscan in fullscreen mode	Shift + PageDown	Shift-Fn + Down arrow
Increase overscan in fullscreen mode	Shift + PageUp	Shift-Fn + Up arrow
Move display down (uses "Display.VCenter")	Alt + PageDown	Cmd-Fn + Down arrow
Move display up (uses "Display.VCenter")	Alt + PageUp	Cmd-Fn + Up arrow
Decrease vertical display size	Shift-Alt + PageUp	Shift-Cmd-Fn + Up arrow
Increase vertical display size	Shift-Alt + PageDown	Shift-Cmd-Fn + Down arrow
Switch to previous display format (NTSC/PAL/SECAM etc.)	Shift-Control + f	Shift-Control + f
Switch to next display format (NTSC/PAL/SECAM etc.)	Control + f	Control + f
Toggle display interpolation	Control + i	Control + i
These settings can also be changed using Global Keys

Palettes Keys (can be remapped)

Function	Key (Standard)	Key (macOS)
Select previous palette (Standard/z26/User/Custom)	Shift-Control + p	Shift-Control + p
Select next palette (Standard/z26/User/Custom)	Control + p	Control + p
Select previous palette attribute	Shift-Alt + 9	Shift-Cmd + 9
Select next palette attribute	Alt + 9	Cmd + 9
Decrease selected palette attribute	Shift-Alt + 0	Shift-Cmd + 0
Increase selected palette attribute	Alt + 0	Cmd + 0
These settings can also be changed using Global Keys

TV effects Keys (can be remapped)

Function	Key (Standard)	Key (macOS)
Select previous TV effects preset	Shift-Alt + 1	Shift-Cmd + 1
Select next TV effects preset	Alt + 1	Cmd + 1
Select previous 'Custom' mode attribute (*)	Shift-Alt + 2	Shift-Cmd + 2
Select next 'Custom' mode attribute (*)	Alt + 2	Cmd + 2
Decrease 'Custom' selected attribute value (*)	Shift-Alt + 3	Shift-Cmd + 3
Increase 'Custom' selected attribute value (*)	Alt + 3	Cmd + 3
Toggle 'phosphor' mode	Alt + p	Cmd + p
Decrease 'phosphor' blend	Shift-Alt + 4	Shift-Cmd + 4
Increase 'phosphor' blend	Alt + 4	Cmd + 4
Decrease scanline intensity	Shift-Alt + 5	Shift-Cmd + 5
Increase scanline intensity	Alt + 5	Cmd + 5
These settings can also be changed using Global Keys
Items marked as (*) will also switch to 'Custom' mode

Developer Keys (can be remapped)

Function	Key (Standard)	Key (macOS)
Toggle frame stats (scanline count/FPS/BS type etc.)	Alt + L	Cmd + L
Toggle TIA Player0 object	Alt + z	Cmd + z
Toggle TIA Player1 object	Alt + x	Cmd + x
Toggle TIA Missile0 object	Alt + c	Cmd + c
Toggle TIA Missile1 object	Alt + v	Cmd + v
Toggle TIA Ball object	Alt + b	Cmd + b
Toggle TIA Playfield object	Alt + n	Cmd + n
Toggle all TIA objects	Alt + Comma	Cmd + Comma
Toggle TIA Player0 collisions	Shift-Alt + z	Shift-Cmd + z
Toggle TIA Player1 collisions	Shift-Alt + x	Shift-Cmd + x
Toggle TIA Missile0 collisions	Shift-Alt + c	Shift-Cmd + c
Toggle TIA Missile1 collisions	Shift-Alt + v	Shift-Cmd + v
Toggle TIA Ball collisions	Shift-Alt + b	Shift-Cmd + b
Toggle TIA Playfield collisions	Shift-Alt + n	Shift-Cmd + n
Toggle all TIA collisions	Shift-Alt + Comma	Shift-Cmd + Comma
Toggle TIA 'Fixed Debug Colors' mode	Alt + .	Cmd + .
Toggle PAL color-loss effect	Control + L	Control + L
Toggle TV 'Jitter' effect	Alt + j	Cmd + j
These settings can also be changed using Global Keys

Global Keys (can be remapped)

These keys allow selecting and changing settings without having to remember the dedicated keys. They keys are grouped by Audio & Video and Debug settings.

Function	Key (Standard)	Key (macOS)
Select previous setting group	Control + End	Control-Fn + Left arrow
Select next setting group	Control + Home	Control-Fn + Right arrow
Select previous setting	End	Fn + Left arrow
Select next setting	Home	Fn + Right arrow
Decrease current setting	PageDown	Fn + Down arrow
Increase current setting	PageUp	Fn + Up arrow

Notes:

• Only available if UI messages are enabled.
• Currently not available settings are automatically skipped.
• If a setting was selected via dedicated key, its value can also be changed with the global keys.

Other Emulation Keys (can be remapped)

Function	Key (Standard)	Key (macOS)
Load previous game in ROM (multicart ROM, TIA mode)	Shift-Control + r	Shift-Control + r
Reload current ROM (singlecart ROM, TIA mode) Load next game in ROM (multicart ROM, TIA mode)	Control + r	Control + r
Reload ROM listing (ROM launcher mode)	Control + r	Control + r
Emulate 'frying' effect (TIA mode)	Backspace	Backspace
Go to parent directory (UI mode)	Backspace	Backspace
Decrease emulation speed (disables 'Turbo' mode)	Shift-Control + s	Shift-Control + s
Increase emulation speed (disables 'Turbo' mode)	Control + s	Control + s
Toggle 'Turbo' mode (maximum emulation speed)	Control + t	Control + t
Decrease autofire rate	Shift-Control + a	Shift-Control + a
Increase autofire rate	Control + a	Control + a
Switch mouse between controller emulation modes (see Game Properties - Controller)	Control + 0	Control + 0
Toggle grab mouse	Control + g	Control + g
Swap Stelladaptor/2600-daptor port ordering	Control + 1	Control + 1
Save continuous PNG snapshots (per interval defined in Snapshot Settings)	Alt + s	Cmd + s
Save continuous PNG snapshots (every frame)	Shift-Alt + s	Shift-Cmd + s
Toggle 'Time Machine' mode	Alt + t	Cmd + t
Enter/Exit the Time Machine dialog	Shift + t to enter, Shift + t/Escape to exit and continue with emulation	Shift + t to enter, Shift + t/Escape to exit and continue with emulation
Playback the Time Machine from current state (without sound, from the TM dialog only)	Shift	Shift
Start/Stop playback (exist/enters the Time Machine dialog)	Shift + Space	Shift + Space
Rewind by one state (enters the Time Machine dialog)	Alt + Left arrow	Cmd + Left arrow
Rewind by 10 states (enters the Time Machine dialog)	Shift-Alt + Left arrow	Shift-Cmd + Left arrow
Rewind all states (enters the Time Machine dialog)	Alt + Down arrow	Cmd + Down arrow
Unwind by one state (enters the Time Machine dialog)	Alt + Right arrow	Cmd + Right arrow
Unwind by 10 states (enters the Time Machine dialog)	Shift-Alt + Right arrow	Shift-Cmd + Right arrow
Unwind all states (enters the Time Machine dialog)	Alt + Up arrow	Cmd + Up arrow

UI Keys in Text Editing areas (cannot be remapped)

Key	Editor Function
Home	Move cursor to beginning of line
End	Move cursor to end of line
Delete	Remove character to right of cursor
Backspace	Remove character to left of cursor
Control-a	Same function as 'Home'
Control-e	Same function as 'End'
Control-d	Same function as 'Delete'
Control-k	Remove all characters from cursor to end of line
Control-u	Remove all characters from cursor to beginning of line
Control-w	Remove entire word to left of cursor
Control-Left	Move cursor to beginning of word to the left
Control-Right	Move cursor to beginning of word to the right
Control-c	Copy entire line to clipboard (not complete)
Control-v	Paste clipboard contents (not complete)

Controller Map

Some Atari (virtual) controllers are simulated with more than one computer controller, and there are several special cases where controllers are active in certain modes only, as the table below shows. Items marked as (+ extra) indicate that the computer controller may not have enough buttons/axes etc. to fully emulate the device, so extra functionality must be mapped to other controllers.

	Computer
Virtual Controller	Keyboard	Joystick	Mouse (auto mode)	Mouse (specific axis)	Stelladaptor/ 2600-daptor
Joystick	✓	✓	✓	✕	✓
Paddles	✓	✓	✓	✓	✓
Booster	✓	✓	✓ (+ extra)	✕	✓ (+ extra)
Genesis	✓	✓ (+ extra)	✓	✕	✕
Keyboard	✓	✓ (+ extra)	✕	✕	✓ (2600-daptor II)
Driving	✓	✓	✓	✕	✓
Trackball/Mouse	✕	✕	✓	✓ (axis ignored)	✓
CompuMate	✓	✕	✕	✕	✕
Light Gun	✕	✕	✓	✓ (axis ignored)	✕
Mindlink	✕	✕	✓	✓ (axis ignored)	✕
AtariVox	N/A	N/A	N/A	N/A	voice (2600-daptor II)
SaveKey	N/A	N/A	N/A	N/A	N/A

Stella's 'Time Machine'

A special feature of Stella is the 'Time Machine' mode. In this mode, Stella automatically creates savestates in regular, user-defined intervals. At any time, the user can interrupt the current emulation and navigate back and forth within the saved timeline. This can be done either by using the Time Machine hotkeys described in Hotkeys - Other Keys or by using the Time Machine dialog. This dialog is automatically entered when using one of the Time Machine hotkeys. The hotkeys continue to function within the dialog.

Time Machine dialog:

The dialog items are explained in the following two tables.

Top row (left to right)

Item	Description
Current state	Shows the currently loaded state's number
'Timeline' slider	Shows the position of the current state in the recorded timeline. A state can be selected by dragging the slider with the mouse. To visualize state compression, small marks split the timeline into five, equally sized state number intervals.
Total states	Shows the total number of save states in the Time Machine

Bottom row (left to right)

Item	Description
Current time	Shows the time of the currently selected state, relative to the first one
'Start/Stop' button	Starts or stops the Time Machine
'Exit' button	Exits the dialog and continues emulation, starting at current state
'Rewind All' button	Navigates back to the begin of the timeline
'Rewind One' button	Navigates back by one state
'Playback' button	Starts playback, starting at the current state (with sound disabled)
'Unwind One' button	Navigates forward by one state
'Unwind All' button	Navigates forward to the end of the timeline
'Save All' button	Saves all Time Machine states to disk
'Load All' button	Loades all states from disk into Time Machine
Navigation info	Informs about the interval of the user's last Time Machine navigation. The interval can vary if the timeline is compressed.
Total time	Shows the total time covered by the save states (aka 'Horizon')

The 'Time Machine' mode can be configured by the user. For details see Developer Options - Time Machine tab.

Advanced Configuration

The default options in Stella are meant to cater to as many situations as possible. As such, you may never need to change many of its options. However, Stella is very configurable, and if you want to change its behaviour in some way, there's likely a configuration option to do so. The remainder of this (lengthy) section details every configurable option.

Using the Command Line

In addition to the built in ROM launcher, Stella can also be used from the commandline (assuming your operating system has a commandline).

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 <direct3d|opengl|opengles2|opengles|software>	Use the given rendering backend (where applicable); default is the best available mode detected.
-vsync <1|0>	Synchronize screen updates to the vertical blank period. This can result in smoother updates, and eliminate tearing.
-fullscreen <1|0>	Enable fullscreen mode.
-center <1|0>	Centers all windows (if possible).
-windowedpos <XxY>	Sets the window position in windowed emulator mode.
-display <number>	Sets the display for Stella's emulator.
-palette <standard|z26|user|custom>	Set the palette to either normal Stella, the one used in the z26 emulator, a user-defined palette, or a custom palette generated from user-defined phase shifts.
-pal.phase_ntsc <number>	Adjust phase shift of 'custom' NTSC palette.
-pal.phase_pal <number>	Adjust phase shift of 'custom' PAL palette.
-pal.hue <number>	Adjust hue of current palette (range -1.0 to 1.0).
-pal.saturation <number>	Adjust saturation of current palette (range -1.0 to 1.0).
-pal.contrast <number>	Adjust contrast of current palette (range -1.0 to 1.0).
-pal.brightness <number>	Adjust brightness of current palette (range -1.0 to 1.0).
-pal.gamma <number>	Adjust gamma of current palette (range -1.0 to 1.0).
-speed <number>	Control the emulation speed (as a percentage, 10 - 1000).
-turbo <1|0>	Enable 'Turbo' mode for maximum emulation speed.
-uimessages <1|0>	Enable or disable display of message in the UI. Note that messages indicating serious errors override this setting, and are always shown.
-audio.enabled <1|0>	Enable or disable sound generation.
-audio.volume <0 - 100>	Set the volume.
-audio.device <number>	Set the audio device (0 = default).
-audio.preset <1 - 5>	Set an audio preset. Numbers in sequence represent presets for 'custom', 'low quality, medium lag', 'high quality, medium lag', 'high quality, low lag' and 'ultra quality, minimal lag'.
-audio.fragment_size <128|256|512|1024|2048|4096>	Set the number of samples in a single fragment processed by the audio driver.
-audio.sample_rate <44100|48000|96000>	Set sound sample output frequency.
-audio.resampling_quality <1|2|3>	Set resampling quality to low (1), high (2) or ultra (3).
-audio.headroom <0 - 20>	Set number of additional half-frames to prebuffer.
-audio.buffer_size <0 - 20>	Set maximum number of additional half-frames to buffer.
-audio.stereo <1|0>	Enable or disable stereo mode for all ROMs.
-audio.dpc_pitch <10000 - 30000>	Set the pitch of Pitfall II music.
-tia.zoom <zoom>	Use the specified zoom level (integer) while in TIA/emulation mode.
-tia.vsizeadjust <-5 - 5>	Adjust the display height of the TIA image
-tia.inter <1|0>	Use interpolation for the TIA image (results in blending/smoothing of the image).
-tia.fs_stretch <1|0>	Stretch TIA image completely while in fullscreen mode, vs. keeping the correct aspect ratio.
-tia.fs_refresh <1|0>	While in fullscreen mode, adapt the display's refresh rate to the game's frame rate to minimize judder. Note: Not available for macOS.
-tia.fs_overscan <0 - 10>	Add overscan to TIA image while in fullscreen mode
-tia.dbgcolors <roygbp>	Assigns the colours (R)ed, (O)range, (Y)ellow, (G)reen, (B)lue and (P)urple to each graphical register P0/M0/P1/M1/PF/BL, respectively. Currently, these change be changed around to apply different colours to the respective register.
-tv.filter <0 - 5>	Blargg TV effects, 0 is disabled, next numbers in sequence represent presets for 'RGB', 'S-Video', 'Composite', 'Bad Adjust' and 'Custom' modes.
-tv.sharpness <number>	Blargg TV effects 'sharpness' (only available in custom mode, range -1.0 to 1.0).
-tv.resolution <number>	Blargg TV effects 'resolution' (only available in custom mode, range -1.0 to 1.0).
-tv.artifacts <number>	Blargg TV effects 'artifacts' (only available in custom mode, range -1.0 to 1.0).
-tv.fringing <number>	Blargg TV effects 'fringing' (only available in custom mode, range -1.0 to 1.0).
-tv.bleed <number>	Blargg TV effects 'bleed' (only available in custom mode, range -1.0 to 1.0).
-tv.phosphor <always|byrom>	Determines how phosphor mode is enabled. If 'always', then the ROM properties entry is ignored, and phosphor mode is always turned on. Otherwise, the ROM properties determine whether phosphor mode is used for each ROM.
-tv.phosblend <0 - 100>	Enable phosphor blending level; 0 implies no mixing, and 100 is full mixing (not recommended). Note that this doesn't actually enable phosphor mode; that is done for each ROM in the ROM properties. Higher blend values will intensify the phosphor effect. Depending on your display and personal preferences, the optimal default for you may vary. Slow LCDs (especially for office use) may only need a low blend of around 30, while fast switching gamer LCDs may need about 70 to look similar to a CRT.
-tv.scanlines <0 - 100>	TV effects scanline intensity, where 0 means completely off. Note: No scanlines in 1x mode snapshots.
-cheat <code>	Use the specified cheatcode (see Cheat section for description).
-loglevel <0|1|2>	Indicates level of logging to perform while the application is running. Zero completely disables logging (except for serious errors), while the remaining numbers show increasingly more detail.
-logtoconsole <1|0>	Indicates that logged output should be printed to the console/commandline as it's being collected. An internal log will still be kept, and the amount of logging is still controlled by 'loglevel'.
-joydeadzone <number>	Sets the joystick axis deadzone area for analog joysticks/gamepads. All values within the deadzone are treated as zero-axis values, while only those values outside are registered as valid input. Accepts a number from 0 - 29, and uses the formula 3200 + number * 1000. So the possible deadzone values range from 3200 to 32200.
-psense <number>	Sensitivity for emulation of paddles when using analog paddles. Valid range of values is from 1 to 30, with larger numbers causing faster movement.
-dejitter.base <0 - 10>	Strength of paddle input averaging.
-dejitter.diff <0 - 10>	Impact of fast paddle movement on input averaging.
-dcsense <number>	Sensitivity for emulation of driving controllers when using a mouse. Valid range of values is from 1 to 20, with larger numbers causing faster movement.
-autofirerate <0 - 30>	Automatic trigger rate of the fire buttons in Hz (0 = disabled)
-joyallow4 <1|0>	Allow all 4 directions on a joystick to be pressed simultaneously.
-modcombo <1|0>	Use modifier(Shift/Alt/Control)-x key combos. This is normally enabled, since the 'Quit' command is tied to 'Control-q'. However, there are times when you want to disable them. E.g. a 2-player game is using either the 'f' or 'r' keys for movement, and pressing Control (for Fire) will perform an unwanted action associated with Control-r or Control-f default keys.
-saport <lr|rl>	Determines how to enumerate the Stelladaptor/2600-daptor devices in the order they are found: 'lr' means first is left port, second is right port, 'rl' means the opposite.
-avoxport <name>	Set the name of the serial port where an AtariVox is connected.
-usemouse <always|analog|never>	Use mouse as a controller as specified by ROM properties in specific case. Always and never are self-explanatory, analog means only for analog-type devices (paddles, trackball, etc.).
-msense <number>	Sensitivity for emulation of paddles when using a mouse. Valid range of values is from 1 to 20, with larger numbers causing faster movement.
-tsense <number>	Sensitivity for emulation of trackball controllers when using a mouse. Valid range of values is from 1 to 20, with larger numbers causing faster movement.
-dsense <number>	Sensitivity for emulation of paddles when using a digital device (ie, joystick digital axis or button, keyboard key, etc.). Valid range of values is from 1 to 20, with larger numbers causing faster movement.
-cursor <0|1|2|3>	Set mouse cursor state in UI/emulation modes.
-grabmouse <1|0>	Locks the mouse cursor in the game window in emulation mode.
-autoslot <1|0>	Automatically change to the next available save state slot after saving a ROM state file.
-saveonexit <none|current|all>	Automatically save no, current or all states when exiting emulation. The latter also loads all states when entering emulation.
-fastscbios <1|0>	Disable Supercharger BIOS progress loading bars.
-threads <1|0>	Enable multi-threaded video rendering (may not improve performance on all systems).
-snapsavedir <path>	The directory to save snapshot files to.
-snaploaddir <path>	The directory to load ROM info viewer snaposhot files from.
-snapname <int|rom>	When saving snapshots, use either the internal database name or the actual ROM filename.
-sssingle <1|0>	Generate single snapshot instead of many, overwriting any previous snapshots.
-ss1x <1|0>	Ignore any scaling applied to the TIA image, and save snapshot in unscaled (1x) mode.
-ssinterval <number>	Set the interval in seconds between taking snapshots in continuous snapshot mode (currently 1 - 10).
-rominfo <rom>	Display detailed information about the given ROM, and then exit Stella.
-listrominfo	Prints relevant contents of the Stella ROM database, one ROM per line, and then exit Stella. This can be used for external frontends.
-exitlauncher <1|0>	Always exit to ROM launcher when exiting a ROM (normally, an exit to launcher only happens when started with the launcher).
-launcherpos <XxY>	Sets the window position in windowed ROM launcher mode.
-launcherdisplay <number>	Sets the display for the ROM launcher.
-launcherres <WxH>	Set the size of the ROM launcher.
-launcherfont <small|low_medium|medium|large|large12|large14|large16>	Set the size of the font in the ROM launcher.
-launcherroms <1|0>	Specifies whether to show ROMs only (the default) or all files in the ROM launcher.
-romviewer <float>	Hide ROM Info Viewer in ROM launcher mode (0) or use the given zoom level. Note: The zoom level is converted into a percentage in the UI.
-uipalette <standard|classic|light>	Use the specified palette for UI elements.
-dialogfont <small|low_medium|medium|large|large12|large14|large16>	Set the size of the font in the dialogs.
-dialogpos <0 - 4>	Set the position of dialogs within Stella windows (0 = center).
-hidpi <0|1>	Enables the HiDPI mode which scales the UI by a factor of two.
-confirmexit <0|1>	Display a popup when emulation is exited.
-listdelay <delay>	Set the amount of time to wait between treating successive keypresses as a single word in file listings (value can range from 300-1000). Use '0' to disable list-skipping completely.
-mwheel <lines>	Set the number of lines the mousewheel will scroll in the UI (1 - 10).
-mdouble <speed>	Set the mouse double click speed in the UI (100 - 900 ms).
-ctrldelay <delay>	Set the delay before controller input will start repeating in the UI (200 - 1000 ms).
-ctrlrate <rate>	Set the controller repeat rate in the UI (2 - 30 repeats/s).
-romdir <dir>	Set the path where the ROM launcher will start.
-followlauncher <0|1>	Make the start path follow ROM launcher navigation.
-maxres <WxH>	Useful for developers, this sets the maximum size of window that can be created, allowing to simulate testing on 'smaller' systems.
-basedir <dir>	Override the base directory for all config files.
-baseinappdir	Override the base directory for all config files by attempting to use the application directory. For now this is only supported in Windows.
-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
-dis.resolve <1|0>	Try to differentiate between code vs. data sections in the disassembler. See the Debugger - ROM Disassembly Settings for more information.
-dis.gfxformat <2|16>	Sets the base to use for displaying GFX sections in the disassembler.
-dis.showaddr <1|0>	Shows/hides opcode addresses in the disassembler.
-dis.relocate <1|0>	Relocate calls out of address range in the disassembler.
-dbg.pos <XxY>	Sets the window position in windowed debugger mode.
-dbg.display <number>	Sets the display for the debugger.
-dbg.res <WxH>	Set the size of the debugger window.
-dbg.fontsize <small|medium|large|>	Set the font size in the debugger window.
-dbg.fontstyle <0|1|2|3>	How to use bold fonts in the debugger window. '0' means all normal font, '1' is bold labels only, '2' is bold non-labels only, '3' is all bold font.
-dbg.ghostreadstrap <1|0>	Debugger considers/ignores 'ghost' reads for trap addresses
-dbg.uhex <0|1>	Lower-/uppercase HEX display
-break <address>	Set a breakpoint at specified address.
-debug	Immediately jump to debugger mode when starting Stella.
-holdjoy0 <U,D,L,R,F>	Start the emulator with the left joystick direction/button held down (ie, use 'UF' for up and fire). After entering the emulation, you will have to press and release the direction again to release the event.
-holdjoy1 <U,D,L,R,F>	Start the emulator with the right joystick direction/button held down (ie, use 'UF' for up and fire). After entering the emulation, you will have to press and release the direction again to release the event.
-holdselect	Start the emulator with the Game Select switch held down. After entering the emulation, you will have to press and release 'Select' to release the event.
-holdreset	Start the emulator with the Game Reset switch held down. After entering the emulation, you will have to press and release 'Reset' to release the event.
-bs <type>	Set "Cart.Type" property. See the Game Properties section for valid types.
-type <type>	Same as using -bs.
-startbank <bank>	Set "Cart.StartBank" property.
-channels <Mono|Stereo>	Set "Cart.Sound" property.
-ld <A|B>	Set "Console.LeftDiff" property.
-rd <A|B>	Set "Console.RightDiff" property.
-tv <Color|BW>	Set "Console.TVType" 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.
-pxcenter <-10..30>	Set "Controller.PaddlesXCenter" property.
-pycenter <-10..30>	Set "Controller.PaddlesYCenter" property.
-ma <Auto|XY>	Set "Controller.MouseAxis" property. See the Game Properties section for valid types.
-format <format>	Set "Display.Format" property. See the Game Properties section for valid formats.
-vcenter <number>	Set "Display.VCenter" property (-5..5).
-pp <Yes|No>	Set "Display.Phosphor" property.
-ppblend <number>	Set "Display.PPBlend" property, used for phosphor effect (0-100). Default is whatever is specified for tv.phosblend.

The following are almost all available in two sets, one for players (prefixed by "plr.") and one for developers (prefixd by "dev."). 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
-dev.settings <1|0>	Select developer (1) or player (0) set.
-<plr.|dev.>stats <1|0>	Overlay console info on the TIA image during emulation.
-<plr.|dev.>detectedinfo <1|0>	Display detected settings info when a ROM is loaded.
-<plr.|dev.>console <2600|7800>	Select console for B/W and Pause key handling and RAM initialization.
-<plr.|dev.>bankrandom <1|0>	On reset, randomize the startup bank (only for selected bankswitch types).
-<plr.|dev.>ramrandom <1|0>	On reset, either randomize all RAM content, or initialize with zero (console = 2600)/startup values (console = 7800) instead.
-<plr.|dev.>cpurandom <S,A,X,Y,P>	On reset, randomize the content of the specified CPU registers.
-dev.tiadriven <1|0>	Set unused TIA pins to be randomly driven high or low on a read/peek. If disabled, use the last databus value for those pins instead.
-dev.rwportbreak <1|0>	Since the 2600 has no dedicated R/W line, different addresses are used for RAM read or write access. If the code reads from such a write address, this causes an unwanted, semi-random write to that address. When this option is enabled, such reads interrupt emulation and the debugger is entered.
-dev.wrportbreak <1|0>	Same as above. If the code writes to such a read address, nothing happens. But a developer should be made aware of it, because this indicates a problem with the code. When this option is enabled, such writes interrupt emulation and the debugger is entered.
-dev.thumb.trapfatal <1|0>	When enabled, this allows the Thumb ARM emulation to throw an exception and enter the debugger on fatal errors. When disabled, such fatal errors are simply logged, and emulation continues. Do not use this unless you know exactly what you're doing, as it changes the behaviour as compared to real hardware.
-<plr.|dev.>eepromaccess <1|0>	When enabled, each read or write access to the AtariVox/SaveKey EEPROM is signalled by a message.
-dev.tia.type <standard|koolaidman| cosmicark|pesco|quickstep|heman|custom>	Set emulated TIA type.
-dev.tia.plinvphase <1|0>	Enable/disable inverted HMOVE clock phase for players (Kool Aid Man glitch).
-dev.tia.msinvphase <1|0>	Enable/disable inverted HMOVE clock phase for missiles (Cosmic Ark stars glitch).
-dev.tia.blinvphase <1|0>	Enable/disable inverted HMOVE clock phase for ball.
-dev.tia.delaypfbits <1|0>	Enable/disable playfield bits delayed by one color clock (stray playfield pixels in Pesco).
-dev.tia.delaypfcolor <1|0>	Enable/disable playfield color delayed by one color clock (colored step borders in Quick Step!).
-dev.tia.delayplswap <1|0>	Enable/disable player swap delayed by one color clock (He-Man title glitch).
-dev.tia.delayblswap <1|0>	Enable/disable ball swap delayed by one color clock.
-<plr.|dev.>tv.jitter <1|0>	Enable TV jitter/roll effect, when there are too many or too few scanlines per frame.
-<plr.|dev.>tv.jitter_recovery <1 - 20>	When TV jitter/roll effect is enabled, determines how long to delay recovery time (recovery spread over multiple frames).
-<plr.|dev.>colorloss <1|0>	Enable/disable the PAL color-loss effect.
-<plr.|dev.>debugcolors <1|0>	Enable/disable the fixed debug colors.
-<plr.|dev.>timemachine <1|0>	Enable/disable the Time Machine
-<plr.|dev.>tm.size <20 - 1000>	Define the Time Machine buffer size.
-<plr.|dev.>tm.uncompressed <0 - 1000>	Define the uncompressed Time Machine buffer size. Must be <= Time Machine buffer size.
-<plr.|dev.>tm.interval <1f|3f|10f|30f| 1s|3s|10s>	Define the interval between two save states.
-<plr.|dev.>tm.horizon <3s|10s|30s|1m|3m| 10m|30m|60m>	Define the horizon of the Time Machine.

Changing Options

All settings can be changed within the integrated Options UI while Stella is running (unless otherwise noted; some settings require an application restart). 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 & Audio Settings dialog (Display):

Item Brief description For more information, see CommandLine Renderer Use specified rendering mode -video Interpolation Enable interpolation of the TIA image -tia.inter Zoom Zoom level of the TIA image -tia.zoom Fullscreen Self-explanatory - Note that colors may slightly change. This depends on the OS and renderer used. -fullscreen Stretch In fullscreen mode, completely fill screen with the TIA image. -tia.fs_stretch Adapt display... In fullscreen mode, adapt the display's refresh rate to the game's frame rate to minimize judder. Note: Not available for macOS. -tia.fs_refresh Overscan In fullscreen mode, add overscan to the TIA image -tia.fs_overscan V-Size adjust Adjust height of the TIA image -tia.vsizeadjust

Video & Audio Settings dialog (Palettes):

Item Brief description For more information, see CommandLine Palette Palette used for emulation mode -palette NTSC phase Adjust phase shift for 'Custom' NTSC palette -pal.phase_ntsc PAL phase Adjust phase shift for 'Custom' PAL palette -pal.phase_pal Hue Adjust hue of currently selected palette -pal.hue Saturation Adjust saturation of currently selected palette -pal.saturation Contrast Adjust contrast of currently selected palette -pal.contrast Brightness Adjust brightness of currently selected palette -pal.brightness Gamma Adjust gamma of currently selected palette -pal.gamma

Video & Audio Settings dialog (TV Effects):

Item Brief description For more information, see CommandLine TV mode Disable TV effects, or select TV preset -tv.filter Adjustable sliders Set specific attribute in 'Custom' TV mode -tv.sharpness, -tv.resolution, etc. Phosphor for all ROMs Enable phosphor mode for all ROMs -tv.phosphor Blend (phosphor) Blend level to use in phosphor mode for all ROMs (needs to be manually adjusted for your particular hardware) -tv.phosblend Scanline intensity Sets scanline black-level intensity. Note: No scanlines in 1x mode snapshots. -tv.scanlines Clone RGB Copy 'RGB' attributes to 'Custom' TV mode sliders   Clone S-Video Copy 'S-Video' attributes to 'Custom' TV mode sliders   Clone Composite Copy 'Composite' attributes to 'Custom' TV mode sliders   Clone Bad adjust Copy 'Bad Adjust' attributes to 'Custom' TV mode sliders   Revert Revert attribute sliders to saved 'Custom' TV mode settings

Video & Audio Settings dialog (Audio):

Item Brief description For more information, see CommandLine Enable audio Self-explanatory -audio.enabled Volume Self-explanatory -audio.volume Device Use the specified audio device. -audio.device Mode Select an audio preset or choose 'Custom' for manual configuration. -audio.preset Fragment size The number of samples in a single fragment processed by the audio driver. Smaller values mean less latency, but may lead to dropouts (depending on OS and hardware). -audio.fragment_size Sample rate Output samples per second. Higher values reduce artifacts from resampling and decrease latency, but may lead to dropouts (depending on OS and hardware). -audio.sample_rate Resampling quality Chooses the algorithm used for resampling (= converting TIA output to the target sample rate). 'High' and 'ultra' use a high-quality Lanczos filter but require slightly more CPU, while 'low' may lead to audible screeching artifacts in some games (notably Quadrun). -audio.resampling_quality Headroom Number of frames to buffer before playback starts. Higher values increase latency, but reduce the potential for dropouts. -audio.headroom Buffer size Maximum size of the audio buffer. Higher values increase maximum latency, but reduce the potential for dropouts. -audio.buffer_size Stereo for all ROMs Enable stereo mode for all ROMs. -audio.stereo Pitfall II music pitch Defines the pitch of Pitfall II music (which may vary between carts). -audio.dpc_pitch IMPORTANT: In order to maintain a stable stream of audio data, emulation speed must be synchronized with the audio hardware. Buffering happens in multiple places (OS = fragment size, Stella = headroom and buffer size) and improves the tolerance to speed fluctuations, but introduces latency which manifests as a lag between audio and video. Too aggressive settings for your combination of hardware and software (high sample rate, low fragment size, low headroom, low buffer size) may lead to audio dropouts whose effect may range from isolated popping artifacts to garbled audio. You can check the system log for related messages. If you get recurring messages about audio overruns and underruns (isolates underruns / overruns are normal and a consequence of host system activity), you might have to adjust your settings.

Emulation dialog:

Item Brief description For more information, see CommandLine Emulation speed Emulation speed -speed VSync Enable vertical synced updates -vsync Turbo Enable 'Turbo' mode for maximum emulation speed. This overwrites 'Emulation speed' setting and disables 'VSync'. -turbo Multi-threading Enable multi-threaded rendering -threads Fast SuperCharger load Skip progress loading bars for SuperCharger ROMs -fastscbios Show UI messages Overlay UI messages onscreen -uimessages Confirm exiting... Display a popup when emulation is exited -confirmexit When entering/exiting emulation: Automatically save no, current or all Time Machine states when exiting emulation. The latter also loads all states when entering emulation. When this is enabled, you can always continue your game session from where you exited it. Even including the Time Machine buffer! -saveonexit Automatically change... Automatically change to the next available save state slot after saving a ROM state file. -autoslot

Input Settings dialog:

This dialog is described in further detail in Advanced Configuration - Event Remapping.

User Interface Settings dialog (2 tabs):

		Item Brief description For more information, see CommandLine Theme Theme to use for UI elements (see examples) -uipalette Dialogs font The font used in the dialogs -dialogfont HiDPI mode Scale the UI by a factor of two when enabled -hidpi Dialogs position Position of dialogs with Stella window -dialogpos Center windows Attempt to center application windows, else position at last position -center List input delay Maximum delay between keypresses in filelist-widgets before a search string resets. -listdelay Mouse wheel scroll Number of lines a mouse scroll will move in list-widgets -mwheel Double-click speed Speed of mouse double-clicks -mdouble Controller repeat delay Delay before controller input repeats -ctrldelay Controller repeat rate Rate of controller input repeats -ctrlrate

This tab is described in further detail in Advanced Configuration - ROM Launcher.

Snapshot Settings dialog:

Item Brief description For more information, see CommandLine Save path Specifies where to save snapshots -snapsavedir Continuous snapshot interval Interval (in seconds) between snapshots -ssinterval Use actual ROM name Use the actual ROM filename instead of the internal database name -snapname Overwrite existing files Whether to overwrite old snapshots -sssingle Create pixel-exact image (no zoom/post-processing) Save snapshot using the exact pixels from the TIA image, without zoom or any post-processing effects -ss1x

Developer Settings dialog:

This tab is described in further detail in Advanced Configuration - Developer Options/Integrated Debugger.

Game Properties dialog:

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

Audit ROMs dialog:

This dialog is described in further detail in Advanced Configuration - ROM Audit Mode.

Event Remapping/Input Devices

Almost every event in Stella can be remapped to another key on the keyboard or to buttons on up to eight joysticks/gamepads (see Getting Started - 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 'Emulation Events' tab. Here you can also filter for the type of events. Otherwise, click the 'UI Events' tab for user interface events.
3. Select event you want to remap and click the 'Map' button.
4. Now define the input:
   • Either press a key, a modifier key (Control, Shift...) or a modifier+key combination.
   • Or use a controller direction, a button or a button+controller direction combination.
   Then that key (combination) or controller action will be bound to the selected event.
   Notes:
   • 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.
   • The same input can be used for multiple controller types (e.g. 'Right' for 'P0 Joystick Right' and 'Paddle 0 Turn Right').
   • If the same input is used again for the same controller type, the old mapping will be removed.
   • Events which are available in both event modes can be remapped individually.
   • Left and right modifiers are mapped separately when used alone.

You can also:

• Cancel a remap in progress by clicking 'Cancel'.
  Note: Pressing 'ESC' will map that key, not abort the mapping.
• Erase all event's mappings by clicking 'Erase'.
• Reset the event to its default mapping by clicking 'Reset'.
• Reset all emulation or UI event mappings to default by clicking 'Defaults'.

The following screenshots illustrate the event remapping process:

Finally there is a 'Combo' button in the 'Emulation Events' tab, accessible only when a Combo event has been selected from the list of events on the left. Clicking 'Combo' will show a dialog similar to the following:

In this dialog, you can assign various events to the selected combo event. Note that this simply assigns multiple events to the combo; you still need to map the combo event itself to some action, as described in the 'remap an event' section above.

Device and port settings can be configured under the 'Devices & Ports' tab, shown below:

Item Brief description For more information, see CommandLine Joystick deadzone size Deadzone area for axes on joysticks/gamepads -joydeadzone (Analog paddle) Sensitivity Sensitivity of an analog paddle -psense Analog paddle) Dejitter averaging Strength of paddle input averaging, suppresses mouse jitter -dejitter.base (Analog paddle) Dejitter reaction Strength of paddle reaction to fast paddle movements, suppresses mouse jitter -dejitter.diff Digital paddle sensitivity Sensitivity used when emulating a paddle using a digital device -dsense Autofire rate Automatic trigger rate of the fire buttons in Hz -autofirerate Allow all 4 directions ... Allow all 4 joystick directions to be pressed simultaneously -joyallow4 Use modifier key combos Enable using modifier keys in keyboard actions -modcombo Swap Stelladaptor ports Swap the order of the detected Stelladaptors/2600-daptors (see Advanced Configuration - Stelladaptor/2600-daptor Support) -saport Joystick database Show all joysticks that Stella knows about, with the option to remove them   Erase EEPROM Erase the whole AtariVox/SaveKey flash memory   AtariVox serial port Described in further detail in Advanced Configuration - AtariVox/SaveKey Support -avoxport

Mouse settings can be configured under the 'Mouse' tab, shown below:

Item Brief description For more information, see CommandLine Use mouse as ... Allow the mouse to emulate various controllers -usemouse (Sensitivity) Paddle Sensitivity used when emulating a paddle using a mouse -msense (Sensitivity) Trackball Sensitivity used when emulating a trackball device using a mouse -tsense (Sensitivity) Driving controller Sensitivity used when emulating a driving controller device using a mouse -dcsense Mouse cursor visibility Show/hide cursor depending on current state -cursor Grab mouse ... Keep mouse in window in emulation mode (only when used as controller) Note: The sensitivity may greatly vary when the mouse is not grabbed. -grabmouse

ROM Launcher

Several options are configurable in the ROM launcher. The size of the launcher and fonts, as well as the 'ROM Info Viewer' can be changed in UI Settings - Launcher dialog, as shown below:

Most of the options are self-explanatory, except for the 'ROM info width', which is described below.

ROM Info Viewer

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. Note that the snapshots can be any size generated by Stella; they will be resized accordingly.

The ROM Info Viewer's width can be defined between 0% (off) and 100%. The value is relative to the launcher width. For too small or too large values, Stella will automatically correct the width at runtime so that the ROM names and the current ROM's information always have enough space.

The following snapshots illustrate the various font sizes and rom info widths:

ROM Info Viewer width at 40%, UI sized 800x480, small launcher font:

ROM Info Viewer width at 32%, UI sized 1000x720, medium launcher font:

ROM Info Viewer width at 50% , UI sized 1280x900, large launcher font:

The text box in the upper right corner can be used to narrow down the results in the ROM listing. When this box is empty, all files are shown (subject to the restrictions from the filtering option, explained below). Typing characters here will show only those files that match that pattern. For example, typing 'Activision' will show only files that contain the word 'Activision' in their name. This is very useful for quickly finding a group of related ROMs. Note that the search is not case sensitive, so you don't need to worry about capital or lower-case letters.

ROM Launcher Context Menu

The ROM launcher also contains a context menu, selected by clicking the right mouse button anywhere in the current window. This context menu contains the following items:

1. Power-on options: Selecting this option shows a dialog whereby ROM properties can be temporarily overridden, and joystick/console buttons can be temporarily held down. Selecting options from this dialog will cause all ROMs launched after that to use those properties you specify. Clicking Defaults will disable its functionality, and use ROM properties as defined by the ROM itself. The dialog is as follows (see Advanced Configuration - Game Properties for more information concerning ROM properties):

   Item For more information, see Commandline Bankswitch type -bs TV type -tv Left difficulty -ld Right difficulty -rd Startup mode -debug Left joy items -holdjoy0 Right joy items -holdjoy1 Console: Select -holdselect Console: Reset -holdreset



2. Show only ROM files: Selecting this reloads the current listing, showing only files that have a valid ROM extension.


3. Show all files: Selecting this reloads the current listing, showing all files (with no restriction on file name).


4. Reload listing: Selecting this performs a reload of the current listing. It is an alternative to pressing the Control-r key combo.

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 with extensions described in "Supported File formats". Files which don't have these extensions will be ignored.
• If a valid ROM doesn't have a properties entry, it will be ignored.

Stelladaptor/2600-daptor Support

Stella supports real Atari 2600 joysticks, paddles, driving controllers and trackballs (CX22/CX80 'Trak-Ball', Atari and Amiga mouse) using the Stelladaptor and 2600-daptor devices.

Stella can use up to two adaptors; any extra ones are ignored. Stelladaptor devices will be automatically detected and configured. The actual controllers can be plugged/unplugged while the emulator is running, although you will need to restart the game currently being emulated.

The detection and configuration is as follows:

• The first device 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, the left driving controller, left keypad, etc.
• The second device 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, the right driving controller, right keypad, etc.
• Any other devices will be ignored.
• The assignment ordering of Stelladaptor/2600-daptor to port can be redefined with 'saport' (see description in Using the Command Line) and dynamically with the 'Control-1' key combo.

AtariVox/SaveKey Support

Stella supports a real AtariVox device for the speech/SpeakJet portion of the controller. You will need a real AtariVox device 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 'Devices & Ports' tab in Advanced Configuration - Input Devices.

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 macOS tend to use names similar to '/dev/xxxxxx'. For now, only Linux/UNIX, macOS, and Windows 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 accessed 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 location of EEPROM files will depend on the version of Stella, as follows:

Linux/Unix	$HOME/.config/stella/nvram/atarivox_eeprom.dat $HOME/.config/stella/nvram/savekey_eeprom.dat
Macintosh	$HOME/Library/Application Support/Stella/nvram/atarivox_eeprom.dat $HOME/Library/Application Support/Stella/nvram/savekey_eeprom.dat
Windows	%APPDATA%\Stella\nvram\atarivox_eeprom.dat %APPDATA%\Stella\nvram\savekey_eeprom.dat
If using 'basedir' or 'baseinappdir'	_BASEDIR_/nvram/atarivox_eeprom.dat _BASEDIR_/nvram/savekey_eeprom.dat

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. You can also reset the EEPROM to a clean state.

Developer Options/Integrated Debugger

Several developer related options can be configured in the 'Developer Settings' dialog. Two sets ('Player settings', 'Developer settings') allow easy adjustment of all settings for different use cases (playing or developing games) at once.

Developer Settings dialog (Emulator)

Item Brief description For more information, see CommandLine Player/Developer settings Selects the active settings set -dev.settings Console info overlay Overlay console info on the TIA image during emulation. -plr.stats -dev.stats Detected settings info Display detected settings when a ROM is loaded. -plr.detectedinfo -dev.detectedinfo Console Select the console type, this affects Color/B&W/Pause key emulation and zero-page RAM initialization -plr.console -dev.console Random startup bank Randomize the startup bank (only for selected bankswitch types) -plr.bankrandom -dev.bankrandom Randomize zero-page ... When loading a ROM, randomize all RAM content instead of initializing with all zeroes (for 'Console' = 'Atari 2600' only) -plr.ramrandom -dev.ramrandom Randomize CPU When loading a ROM, randomize the content of the specified CPU registers -plr.cpurandom -dev.cpurandom Drive unused TIA pins ... Unused TIA pins are read random instead of the last databus values -dev.tiadriven Break on reads from ... A read from a write port interrupts emulation and the debugger is entered. -dev.rwportbreak Break on write to ... A write to a read port interrupts emulation and the debugger is entered. -dev.wrportbreak Fatal ARM emulation ... Thumb ARM emulation throws an exception and enters the debugger on fatal errors -dev.thumb.trapfatal Display AtariVox... Display a message when the AtariVox/SaveKey EEPROM is read or written -plr.eepromaccess -dev.eepromaccess

Developer Settings dialog (TIA):

Item Brief description For more information, see CommandLine Chip type Type of emulated TIA chip. Allows testing for TIA versions which exhibit timing problems in certain games. The 'Custom' option allows testing for glitch combinations. -dev.tia.type Inverted HMOVE clock... Emulates the Kool-Aid Man collision and Cosmic Ark stars glitches for the given objects. -dev.tia.plinvphase -dev.tia.msinvphase -dev.tia.blinvphase Delayed Playfield Emulates playfield registers delayed by one color clock. This e.g. causes glitches in Pesco (stray playfield pixel) and Quick Step! (colored step borders) -dev.tia.delaypfbits -dev.tia.delaypfcolor Delayed VDEL... swap for Emulates a VDELP0/P1/BL swap delayed by one color clock. This e.g cause glitches in the He-Man title screen. -dev.tia.delayplswap -dev.tia.delayblswap

Developer Settings dialog (Video):

Item Brief description For more information, see CommandLine Jitter/roll effect Emulate screen roll with inconsistent scanline count -plr.tv.jitter -dev.tv.jitter (Jitter/roll) Recovery Determines recovery time for screen rolling -plr.tv.jitter_recovery -dev.tv.jitter_recovery PAL color-loss Use PAL color-loss effect -plr.colorloss -dev.colorloss Debug colors Use fixed debug colors -plr.debugcolors -dev.debugcolors Player 0 Missile 0 Player 1 Missile 1 Playfield Ball Set color for specific object in 'Debug Colors' mode (PF0, PF1 and PF2 have a slightly different luminance) Disabled in ROM launcher mode -tia.dbgcolors

Developer Settings dialog (Time Machine)

Item Brief description For more information, see CommandLine Time Machine When the Time Machine is enabled, Stella will automatically buffer save states in the interval described below. The user can then navigate back and forth within the recorded timeline. Note: This buffer is identical with the one described in Debugger - Global Buttons. It is independent from the save states manually created with F9. -plr.timemachine -dev.timemachine Buffer size Defines the Time Machine buffer size. The larger the buffer, the less save states have to be compressed to reach the horizon. -plr.tm.size -dev.tm.size Uncompressed size (*) Defines the uncompressed Time Machine buffer size. States within this area will not be compressed and keep their initial interval. -plr.tm.uncompressed -dev.tm.uncompressed Interval Defines the interval between two save states when they are created. -plr.tm.interval -dev.tm.interval Horizon Defines the horizon of the Time Machine. A large horizon allows going back further in time. To reach the horizon, save states will be compressed (*). This means that more and more intermediate states will be removed and the interval between save states becomes larger the further they are back in time. (*) Compression only works if 'Uncompressed size' is smaller than 'Buffer size'. -plr.tm.horizon -dev.tm.horizon

Developer Settings dialog (Debugger)

Item Brief description For more information, see CommandLine Font size Self-explanatory -dbg.fontsize Font style Self-explanatory -dbg.fontstyle Debugger width/height Self-explanatory -dbg.res Trap on 'ghost' reads Defines whether the debugger should consider CPU 'ghost' reads for trap addresses. -dbg.ghostreadstrap

Many more options are available for ROM developers, which are described in different sections of this manual, as follows:

• Developer key-combo shortcuts, used to change TIA state dynamically (ie, while the emulation is still running). See Keyboard Layout - Developer Keys in TIA mode for more information.
• Commandline options influencing emulation state. See Using the Command Line - Developer Commands for more information.
• Viewing TIA/console information overlaid on the TIA image. This option can be enabled from the commandline or using the Alt-L key combo, and is extremely useful for viewing the current scanline count and associated frames per second, bankswitch and display formats, etc. The following shows an example of this information:

  

  The three lines of output describe the following:

  1. Number of scanlines in current frame, associated framerate, and resulting display format. Note that the framerate shown is the internal, virtual framerate (it's calculated from the number of scanlines). If the '*' character is present, it means the display format was auto-detected as shown. For the given example, the format was auto-detected as 'NTSC'.
  2. Effective emulation speed displayed as frames per second and user defined emulation speed displayed as percentage relative to normal speed.
  3. Cartridge information. If the '*' character is present, it means the bankswitch format was auto-detected as shown. The item in round brackets indicates ROM size. For the given example, the bankswitch type was auto-detected as 4K, and the file size was 4K (4096 bytes).

Finally, Stella contains an extensive, built-in debugger. Have a look at this page for integrated debugger documentation.

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 opengl	video = opengl
-volume 75	volume = 75
-center 1	center = 1 (or center = true)

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

Linux/Unix	$HOME/.config/stella/stellarc
Macintosh	Not applicable; settings are saved in $HOME/Library/Preferences/Stella-emu.plist
Windows	%APPDATA%\Stella\stella.ini
If using 'basedir' or 'baseinappdir'	_BASEDIR_/stellarc (or stella.ini)

Cheatcode Manager

Stella 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 hexadecimal 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 will depend on the version of Stella, as follows:

Linux/Unix	$HOME/.config/stella/stella.cht
Macintosh	$HOME/Library/Application Support/Stella/stella.cht
Windows	%APPDATA%\Stella\stella.cht
If using 'basedir' or 'baseinappdir'	_BASEDIR_/stella.cht

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

Viewing the System Log

Stella maintains a log of its operations when the program first starts up, and while it is running. In older releases, this information was only viewable from the commandline. However, the current release allows you to see this information from within the UI. This can be selected from the main Options menu, where it is labelled "System Logs". Clicking on the button will show a window similar to the following:

Item For more information, see Commandline Log level -loglevel Print to console -logtoconsole

The log levels are self-explanatory (None, Basic, Verbose). The "Print to console" option emulates the behaviour of older versions of Stella, whereby the logged output is also shown on the commandline from which Stella was launched (if it was launched in that fashion). Finally, the current contents of the system log can be saved to your home directory by clicking the "Save log to disk" button.

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 or within the corresponding Game Properties dialogs. This 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
   "Cart.MD5"  "Value"
   "Property"  "Value"
   ""

   ; Comments
   "Cart.MD5"  "Value"
   "Property"  "Value"
   ""

   . . .

   ; Comments
   "Cart.MD5"  "Value"
   "Property"  "Value"
   ""

Every block in the property file must have a unique value for the Cart.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:

Cart.Type:	Indicates the bank-switching type for the game. The value of this property must be either Auto or one of the following (for more information about bank-switching see Kevin Horton's 2600 bankswitching document or the documentation in each cartridge's source code file) types. Types marked as (¹) do currently have no reliable auto-detection, those marked as (²) are not fully supported in the debugger:  Type  Description File Extension (to force type) 0840 8K ECONObanking .084, .0840 2IN1 ¹ 4-32K Multicart (2 games) .2N1 4IN1 ¹ 8-32K Multicart (4 games) .4N1 8IN1 ¹ 16-64K Multicart (8 games) .8N1 16IN1 ¹ 32-128K Multicart (16 games) .16N, .16N1 32IN1 ¹ 64-128K Multicart (32 games) .32N, .32N1 64IN1 ¹ 64/128K Multicart .64N, .64N1 128IN1 ¹ 256/512K Multicart .128, .128N1 2K 32-2048 bytes Atari .2K 3E 512K Tigervision + 32K RAM .3E 3EX 512K Tigervision + 256K RAM .3EX 3E+ 3E+ (TJ modified 3E) .3EP, .3E+ 3F 512K Tigervision .3F 4A50 ² 64K 4A50 + RAM .4A5, .4A50 4K 4K Atari .4K 4KSC CPUWIZ 4K + RAM .4KS, .4KSC AR ² Supercharger .AR BF CPUWIZ 256K .BF BFSC CPUWIZ 256K + RAM .BFS, .BFSC BUS Experimental .BUS CDF Chris, Darrell, Fred (includes CDFJ) .CDF CM ¹ Spectravideo CompuMate .CM CTY ² CDW - Chetiry .CTY CV CommaVid extra RAM .CV DF CPUWIZ 128K .DF DFSC CPUWIZ 128K + RAM .DFS, .DFSC DPC Pitfall II .DPC DPC+ Enhanced DPC .DPP, .DPC+ E0 8K Parker Bros .E0 E7 16K M-network .E7 E78K 8K M-network .E78, .E78K EF 64K Homestar Runner .EF EFSC 64K Homestar Runner + RAM .EFS, .EFSC F0 Dynacom Megaboy .F0 F4 32K Atari .F4 F4SC 32K Atari + RAM .F4S, .F4SC F6 16K Atari .F6 F6SC 16K Atari + RAM .F6S, .F6SC F8 8K Atari .F8 F8SC 8K Atari + RAM .F8S, .F8SC FA CBS RAM Plus .FA FA2 CBS RAM Plus 24/28K .FA2 FC Amiga Power Play Aracde 16/32K .FC FE 8K Decathlon .FE MDM Menu Driven Megacart .MDM SB 128-256K SUPERbanking .SB TVBOY 512K TV Boy (127 games) .TVB, .TVBOY UA 8K UA Ltd. .UA UASW 8K UA Ltd. (swapped banks) .UASW WD Wickstead Design (Pink Panther) .WD WDSW Wickstead Design (Pink Panther) (bad) .WDSW X07 ¹ 64K AtariAge .X07
Cart.StartBank:	Indicates which bank to use for reading the reset vector.
Display.Format:	Indicates the television format the game was designed for. The value must be Auto or one of the following. Types marked as (¹) do currently have no reliable auto-detection. A format can be enforced by using one of the following pattern in the filename.  Format  Filename Pattern (to force format) NTSC NTSC, NTSC60, NTSC 60, NTSC-60 PAL PAL, PAL50, PAL 50, PAL-50 SECAM ¹ SECAM, SECAM50, SECAM 50, SECAM-50 NTSC50 ¹ NTSC50, NTSC 50, NTSC-50 PAL60 ¹ PAL60, PAL 60, PAL-60 SECAM60 ¹ SECAM60, SECAM 60, SECAM-60
Display.VCenter:	Indicates the offset for the vertical center of the display. The value must be n such that -20 <= n <= 20.
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 whatever is specified for tv.phosblend.
Cart.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 mods. The value must be Mono or Stereo.

Console.TVType:	Indicates the default television setting for the game. The value must be Color or BW.
Console.LeftDiff:	Indicates the default difficulty setting for the left player. The value must be A or B.
Console.RightDiff:	Indicates the default difficulty setting for the right player. The value must be A or B.

Controller.Left: Controller.Right:	Indicates what type of controller the left and right player uses. The value must be either Auto or one of the following types. Types marked as (¹) do not have auto-detection yet.  Type  Description Joystick Atari's famous black joystick that was originally included with the system. BoosterGrip ¹ A controller add-in that plugs directly into the joystick port and provides a pass-through for the joystick. In doing so, it provides the two independent buttons. Paddles Standard paddle controllers for use with games such as Breakout and Warlords. One pair of controller per connector (allows for 4-player Warlords). Paddles_IAxis ¹ Same as Paddles, except the axes are inverted. Paddles_IAxDr ¹ Same as Paddles, except both the axes and direction of movement are inverted. Driving ¹ Looks like a paddle, but allows 360° movement. Only one unit per connector, unlike paddles which were sold in pairs. Keyboard Also known as the Star Raiders controller, functionally identical to the Kid's Controller and Keyboard Controller. Game included an overlay with commands, for use with Star Raiders. AmigaMouse Commodore Amiga computer mouse. AtariMouse Atari ST computer mouse. Trakball Standard Atari 2600 CX22/CX80 'Trak-Ball' controller. AtariVox ¹ A SpeakJet based unlimited-vocabulary speech/sound synthesizer with 32K EEPROM. SaveKey A 32K EEPROM for saving high scores, etc. (the EEPROM portion of an AtariVox). Genesis Sega Genesis controller, which can be used similar to a BoosterGrip, giving an extra button. CompuMate ¹ Spectravideo CompuMate (if either left or right is set, CompuMate is used for both). Lightgun Atari XG-1 compatible Light Gun Mindlink ¹ Mindlink controller. KidVid ¹ KidVid controller, limitted suport (8, 9 and 0 start the games).
Console.SwapPorts:	Indicates that the left and right ports should be swapped internally. This is used for ROMs like 'Raiders of the Lost Ark' where the Player 0 joystick is plugged into the right joystick port. The value must be Yes or No.
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.
Controller.PaddlesXCenter:	Defines the horizontal center of the paddles (range -10..30).
Controller.PaddlesYCenter:	Defines the vertical center of the paddles (range -10..30).
Controller.MouseAxis:	Indicates how the mouse should emulate virtual controllers. In 'Auto' mode, the system decides how to best use the mouse. Otherwise, XY indicates how to use the X/Y axis (ie, 02 is paddle0/paddle2). Currently, the mouse X-axis and left button are tied together, as are the Y-axis and right button. The value must be Auto or XY, as follows:  Id  Controller 0 Paddle 0 1 Paddle 1 2 Paddle 2 3 Paddle 3 4 Driving 0 5 Driving 1 6 MindLink 0 7 MindLink 1 An optional second parameter (default of 100) indicates how much of the paddle range that the mouse should emulate.

Cart.Name:	Indicates the actual name of the game. When you save snapshots, load/save state files, or use the ROM Audit Mode functionality, this is the name that will be used for the respective file(s).
Cart.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.
Cart.Manufacturer:	Indicates the game's manufacturer.
Cart.ModelNo:	Indicates the manufacturer's model number for the game.
Cart.Rarity:	Indicates how rare a cartridge is, based on the scale described on AtariAge.
Cart.Note:	Contains any special notes about playing the game.

The buttons at the bottom of the dialogs work as follows:

• Defaults: Reset the properties to those built into Stella.
• Save: Save the properties for the currently selected ROM only to a properties file in the users default save directory.
• OK: Merge/commit any changes into the ROM properties database, which contains info on all ROMs.
• Cancel: Revert any changes in the dialog, and cancel the operation.

The name of the properties file will depend on the version of Stella, as follows:

Linux/Unix	$HOME/.config/stella/stella.pro
Macintosh	$HOME/Library/Application Support/Stella/stella.pro
Windows	%APPDATA%\Stella\stella.pro
If using 'basedir' or 'baseinappdir'	_BASEDIR_/stella.pro

Note: For manual changes to the property files Stella will require a restart to take effect.

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.
custom	A palette generate from user-defined phase shift.

A user-defined palette has certain restrictions, 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 will depend on the version of Stella, as follows:

Linux/Unix	$HOME/.config/stella/stella.pal
Macintosh	%HOME/Library/Application Support/Stella/stella.pal
Windows	%APPDATA%\Stella\stella.pal
If using 'basedir' or 'baseinappdir'	_BASEDIR_/stella.pal

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 (in Video Settings dialog). The current ROM will have to be reloaded for changes to this file to take effect.

Acknowledgments

Bradford W. Mott started developing Stella during the fall of 1995, and Stephen Anthony has maintained the project since around 2004. Over the years, 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. A (likely incomplete) list of the people who have played a part in bringing Stella to you is available on the main Stella webpage Credits List. If we've missed someone, please let us know.

License and Disclaimer

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