TOP | Description | Documentation | Screenshots | Ports | Download | Forum | Credits


Generator is a platform independent sega mega drive / genesis emulator, this is the documentation for the console version (svgalib, dos) version 0.33 and later.

Compiling Generator

Generator is open source, so the source code is available for you to download and compile yourself. Unless you are a developer with a need to do this, or you have a system that doesn't have a pre-compiled binary, I would advise against this route. There are a number of #defines in the source that you have to set correctly for your processor/os and lots of tweaks that can be done in order to get Generator working optimumly.

The source is available at

Pre-compiled binary releases

These versions of Generator are available:

Running Generator


Generator uses svgalib to run under Linux. You will need to install svgalib first. If you use debian, you will probably want package svgalibg1, but don't quote me on that.

For DOS, since it has direct access to SVGA memory anyway, you don't need anything except the binary release.

Of course, you also need some ROMs. The console does not have any proprietary BIOS so there is no additional code to find. To get the ROMs you need to have a legal copy of the cartridge and a cartridge copier. The copier will then save the ROM from the cartridge to disk.

Setting up svgalib

This is the most difficult bit in getting Generator to work under Linux. The svgalib configuration file is at /etc/vga/libvga.config, and you will need to edit it so that svgalib knows about your graphics card.

My advice is to use the VESA driver, I've never had much luck using the other drivers for a specific card, and most modern video cards have good VESA support. This means you should load your libvga.config file and comment-in the line 'chipset VESA' and comment-out all other chipset lines.

Recent svgalibs have mode lines that you can insert, I've never had any need for these lines, the vesa bios is supposed to do all this for you.

Generator requires 640x480 screen resolution at either 15 or 16 bit.

Loading a game

Games are stored as ROM files, so-called because they are copies of the ROM (read only memory) area of the original cartridge.

Place the ROM name on the command line after any command line parameters. Generator supports both .rom and .smd (interleaved) formats. It will automatically detect the format. Although Generator ignores the extension of the file, if it does not match the detected format a warning is displayed.

If the ROM identifies itself as for europe and not for usa or japan then PAL mode will be automatically selected.

Generator will report information on the game it has loaded in this format:

  Loaded 'Sonic The Hedgehog'/'Sonic The Hedgehog' (00001009-00 264A JUE)

The first name is known as the domestic name, and the second is the overseas name. This is from the perspective of Japan.

The three items in brackets are: version, checksum and country information, respectively. The checksum is calculated by Generator - if it does not match with the checksum in the ROM header a warning is emitted. The country information is a set of letters:

  J = Japan
  U = USA
  E = Europe

It may also be a single hex digit which represents a new-style country code.

Command-line options

-v <verbose level>

Generator has many levels of logging:

      0 - REQUEST (unmaskable)
      1 - CRITICAL
      2 - NORMAL (default)
      3 - VERBOSE
      4 - USER
      5+ are debugging levels

As well as being able to select the log level at run-time, log levels can also be compiled out. By default only 0-4 are compiled in.

-l <sound latency>

As emulation is processor intensive, many systems are not able to emulate the console at 100%. If an emulator can't keep up, the first thing you'll notice is breaks in sound and a slow down of the game speed. Generator has been written to try and avoid breaks in sound by detecting when it will run out of sound data and cutting corners in the video output.

The sound latency option is a number indicating how many video fields worth of sound data it should try and keep buffered in memory. A video field is 1/50th or 1/60th of a second depending on whether the game is PAL or NTSC.

When the amount of sound data in the buffer goes above the threshold, Generator will plot the next video frame. When the amount of sound data in the buffer goes below the threshold, Generator will not plot the next video frame, so that it can 'catch up' (plotting involves talking to your video card, which involves talking on the slow PCI/AGP bus, so skipping a frame of video saves a lot of time).

The default value is 5, which equates to an 83ms sound latency.

If you have a fast computer and you can notice the delay in sound, try reducing the amount. Reducing to 0 is a bad idea, it means if your computer can't keep up for just one frame you will get a sound click.

If you have a slow computer, you can increase this value - try 10 in combination with 20 fragments - i.e. -l 15 -f 20, but remember, the larger the value of -l the bigger the latency, and you'll start to notice the time lag.

-f <sound fragments>

This sets the number of sound buffer fragments. Think of -l as the minimum number of frames of sound Generator should try and buffer, and -f as the maximum number of frames of sound Generator can buffer, and you'll be ok :)


The -s flag will save the ROM and exit. The saved ROM will have been converted to linear (as opposed to interleaved .smd) format, and will be saved with filename '<overseas> (<crc>-<country>)', e.g.:

    Sonic The Hedgehog (264A-JUE)

The save will not overwrite any existing files - that is an error.

-d <work dir>

The -d option tells Generator where to save or load files that it uses. Typically this is for save state files, but also affects the -s option. See the save state section for information on the files that are saved.

-i <interlace mode>

Effects how the full-screen mode de-interlaces interlaced screens, can be one of: bob, weave or weave-filter. See the section Interlace for more details on this option.

-j <pad1>,<pad2>

This sets the input devices for each joypad. The default is key0,none. The options are:

Main keyboard (buttons=ASD d-pad=arrows)
Left side of keyboard (buttons=ZXC d-pad=DGRF)
Right side of keyboard (buttons=,./ d-pad=arrows)
Joystick 0
Joystick 1


The keys below are for a single keyboard player, see the -j option to switch to joypad or left/right side of keyboard.

The directional pad is simply the arrow keys.
The three buttons A, B and C can be accessed using either A, B and C or A, S and D.
To quit, press ESCAPE.
Function keys
F1 - License
This shows you the license under which you are using Generator.
F2 - Save/load state
This allows you to save your position to disk (aka cheating).
F4 - Save image
This allows you to save a raw (3 bytes per pixel, red, green, blue) image. You can save either a full-screen (640x480) image or just the game screen (the size varies, it will tell you when it saves). Use the pnm utils to convert the raw file. e.g.
rawtoppm 640 480 sonic2.ss1 | pnmscale -xscale 0.3 
  -yscale 0.3 | pnmtopng >sonic2a.png
F5 - Toggle info
By default the Generator logo, key bindings, date/time are displayed on the screen. This will turn them off.
F6 = Toggle video
This will toggle between PAL and NTSC emulation. Many games will not function correctly if you choose the wrong one. When Generator loads a ROM for the first time it will automatically select PAL if the ROM identified itself as for Europe. Since this option changes the framerate, number of clocks in different parts of the display, etc. you should generally reset the cartridge (F12) after changing this.
F7 - Toggle country
The ROM can ask the system what country the console was built for. This allows you to change the option Generator will report to the ROM. By default this is set to Overseas (USA/Europe) rather than Domestic (Japan). Some games will change their language or title depending on this option. Generally you should reset the cartridge (F12) after changing this.
F8 - Toggle plotter
Generator has two video plotters. The first is a fully-fledged line based plotter which supports all the features of the console's video processor. The second is a cell-based plotter which only supports the abilities of the video processor that can be done on a cell-by-cell basis (a cell is an 8x8 pixel block). The cell-based plotter is much faster - you should use this plotter if your machine isn't quite fast enough or if the ROM doesn't appear to need the line-based plotter's features. There are some things that Generator can't emulate without being in the line-based plotter mode, but these things are rarely used, so typically you do not need to worry about upsetting a game by changing this option as on the whole this is just changing your display.
F9 - Toggle vsync
Generator can synchronise itself to the video card's refresh signal if you desire. This is effectively introducing a wait state into Generator's emulation and wastes time. On the other hand, without the vsync the video card could be displaying a mixture of the previous video frame and the next, causing shearing on the screen. Also, some video cards do not take kindly to omitting the vsync and actually pause or corrupt the display, seemingly for no reason, every few seconds or so. If your video card exhibits this behavior then you will want to turn vsyncs on (some S3 cards do this).
F10 - Full screen
Turning on full screen means Generator has to plot 4 times as much data as it had to before - this will be slower as this has to be transferred over your PCI/AGP bus. If full screen is on then 'Toggle info' (F5) can be used to display the clock/fps at the bottom of the screen. Full screen mode is the only way interlace can be done properly.
F12 - Hard/soft reset
This performs a hard or soft reset. A hard reset is the same as turning off the console and turning it back on again (useful if you change the country or video type using F6 or F7). It will also reset your sound system. A soft reset is the same as pressing the reset button on the console. Technically this means the 68000 processor is reset but no other sub-systems are.

Save State

Newer versions of Generator have the ability to save state to disk in order to let you load and save your position during play. During game you can press F2 followed by 1 to load and 2 to save. You will be presented with 9 slots to save your game into.

These slots are per-game, so you can save up to 9 states for each ROM in your collection. The save games are stored with the same leafname but with the extension .gt<n> where n is the slot number.


I test generator on my P200 DOS machine and games are quite playable, so if your machine is this sort of speed or faster, you shouldn't be having a problem with speed. Machines that are P350 or higher will generally get around 50-60fps.
Sound is choppy
This is unusual as Generator will dynamically drop frames until the sound is not choppy. Try adding -l 15 -f 20 to the command line, if it is still choppy, send me an email, I'd love to investigate.
Half-second pauses every few seconds
This happens on my built-in S3 graphics card on my laptop - it doesn't like Generator not using vsyncs - turn them on (F9) and perhaps this will solve the problem for you.
Screen flickers every now and again
Sometimes your monitor will look like it has lost sync every now and again (perhaps every 10 seconds or so) - this is caused by Generator not using vsyncs and is a problem with your video card not liking the page flip occuring at a particular time. You will need to turn on vsyncs to fix this (my GeForce MX card does this).
Everything ok, just sooo slow
Turn off the slow plotter in favour of the cell-based plotter. Make sure you keep the defaults of vsyncs turned off and don't use full-screen mode. If you feel Generator is still running too slow for you, send me an email telling what you're experiencing.
Generator exits for no reason
Try turning up the verbosity in logging with -v 4. If that still doesn't explain a mystery quit, please drop me an email with details so that I can investigate (it's probably the cpu core aborting, although I haven't seen this in a long time).
Switching to and from X corrupts display
svgalib and X do not work well together - recent versions of svgalib will automatically switch out of X to run and switch back in to X when completed (console output can be seen with CTRL-SHIFT-F8). However, under no circumstance should you switch into X whilst Generator is running, this will corrupt the screen. There is nothing that can be done about this. My advice is always move to a text console before running Generator by doing CTRL-SHIFT-F1 and move back to X when you have finished with CTRL-SHIFT-F7 (the exact F key may be different on your machine).


Some games switch into interlace mode in order to have more resolution. The best example of this is Sonic 2 two-player split-screen mode. Generator supports this mode but needs to de-interlace the screen, which is actually more complicated than it sounds.

An interlaced screen is one where the resolution is doubled, but only half the screen is present in each field of video. There are two methods of fixing this: bob and weave.

The bob de-interlacing technique is to interpolate the lines of each field that don't exist, which basically involves doubling up the pixels in the vertical direction of each field in order to make a frame. This has the side-affect that the screen appears to bob up and down (hence the name). When Generator is not in full-screen mode, and therefore doesn't have the resolution to do anything else, it is basically using a form of bobbing without the actual interpolating.

When in full-screen mode, Generator can use the weave technique by combining the even and odd fields together to form a complete frame. Unfortunately because each field is seperated in time by a 60th of a second, this causes an effect known as combing where there is motion.

To reduce combing Generator can use vertical filtering to smooth out the combing effect, but this has the side effect of introducing a perceived double image effect. This is normally a lot less noticable than the combing, and is therefore the default.

Generator can't do this due to lack of computational time, but the next step would be to do motion-adaptive de-interlacing which switches between bob, weave and filtering depending on whether objects are stationary or moving. This is what good DVD players do when playing to non-interlacing devices (CRTs, plasma, projector, etc).

See the command line option -i to change the interlace style.


There are already three ports of Generator to the Amiga, Mac and Windows. If you would like to port Generator then, as it is open source, you are of course free to do so; but, I will go beyond that and say I will help you out. I'm always available at the end of an email. The other porters are friendly guys too, so there's lots of help available from people who have experience with endian issues, performance issues, etc.


If you have a bug report, either emulation wise or because Generator doesn't work on your platform, send me an email!


I have a to-do list (in my head) but if you don't tell me what you'd like to see from Generator, then I won't know what is important to you. Please drop me an email telling me what you miss from Generator.


Open source only works if you either contribute code or communicate your support to the author. This documentation is being written because someone told me they didn't think there was enough for Generator. So, if there's something you don't like or could be better, don't sit there - tell me about it!