BlastEm

BlastEm is an accurate emulator for the Sega Mega Drive, with early Sega Master System support. It is currently the emulator of choice for Genesis VGM logging. Except for games which cannot be logged or logged properly in BlastEm, logs made in Kega Fusion or Gens will be rejected.

Whereas the current Release of BlastEm, 0.6.2, cannot log VGMs, beta version 0.6.3 can log VGMs. Its "nightly builds" tend to be very stable and can be trusted to be safe to use.

Note: If you've already downloaded BlastEm 0.6.3, newer builds may have improvements that affect VGM logs. I strongly advise staying up to date.

Download

From the list of nightly builds, choose the most recent filename that matches your Operating System.

Logging Advice

BlastEm's hotkeys are listed at the beginning of default.cfg.

Before you start logging VGMs, there are some things you should check:

Are you using the most recent 0.6.3 nightly?

Logs made in nightly ab3d8759da08 and newer sound better than logs from older builds. You can copy your default.cfg file to the new nightly's directory to keep all your settings from before.

Have you already changed the the places BlastEm will save your logs and screencaps ("save paths")?

If not, read the section about it below.

Do you know what framerate (NTSC/60 fps or PAL/50 fps) the game should be logged in?

Check 50Hz Mega Drive Games to find out, then make sure the game plays at the right speed when loaded. If the 50hz game is running at 60 fps, then:

• Go into "System" in the settings, then change Default Region to "E - Europe". If needed, you can hard reset by pressing F5. Multi-region ROMs that officially include Europe will run at 50hz, but others may still run at 60hz. To force PAL mode:
• Launch BlastEm from the command line, using the incantation blastem -r E. You can also place this line in a .bat file, or use the program Kaijuu to make it a menu-click option.
• If the game will not play in PAL mode despite the methods above, you'll have to hack it or ask for help in VGMRips' IRC.

Avoid closing BlastEm before you stop a VGM log. The EOF Offset won't be set correctly, and for some reason vgm_ptch won't work to fix it. Nor apparently can you hand-fix this, even if you look at the VGM Specification.

Most commonly used (default) BlastEm hotkeys in logging

m	Begin or stop VGM logging
p	Take a screenshot
u	Open the debugger

MegaDrive models?

You might be wondering about the Model (MegaDrive model) setting. The default Model settings of BlastEm shouldn't need changing except in rare, special circumstances. This would be when tracks are affected by the Model 1 slowdown bug, like in Dinosaurs for Hire and EarthWorm Jim.

The preferred model to use instead is not known yet. On Romhacking.net, you may be able to find a patch that fixes it. I have yet to see if the same fixes work cross-game.

Command Line Usage

Accurate as of 0.6.3-pre-8990c2f431b1 (date September 3; options may change in later builds):

blastem [OPTIONS] ROMFILE [WIDTH] [HEIGHT]

Options

-h	Print this help text
-r (J, U, or E)	Force region to Japan, US or Europe respectively
-m MACHINE	Force emulated machine type to MACHINE. Valid values are: sms - Sega Master System/Mark III gen - Sega Genesis/Megadrive media - Media Player
-f	Toggles fullscreen mode
-g	Disable OpenGL rendering
-s FILE	Load a GST format savestate from FILE
-o FILE	Load FILE as a lock-on cartridge
-d	Enter debugger on startup
-n	Disable Z80
-v	Display version number and exit
-l	Log 68K code addresses (useful for assemblers)
-y	Log individual YM-2612 channels to WAVE files

Making Paths for Your VGMs and Screenshots

Before logging, you will probably want to change the following path settings in default.cfg:

initial_path $HOME
screenshot_path $HOME
vgm_path $HOME

These paths use the special variable $HOME, which places screenshots and VGMs directly in your User folder. This is probably not what you want.

Many custom folder structures are possible with these settings, but let's start simple.

To store things in BlastEm's folder, change $HOME to $EXEDIR. I've made this change to all three lines above in my default.cfg. The problem is, you'll still end up with a mess with no further changes. We also need these two settings:

screenshot_template $ROMNAME/%Y%m%d_%H%M%S.png
vgm_template $ROMNAME/%Y%m%d_%H%M%S.vgm

These lines work off screenshot_path and vgm_path above. They've been modified from what you'll see in default.cfg. With $ROMNAME in place like so, BlastEm will put each screenshot and VGM into a subfolder matching the loaded ROM's name.

But now, depending on how long the full path (all folder nesting + filename) for a logged VGM is, we may encounter a different problem. If it's too long for your computer's file system, BlastEm will silently fail to log.

If the two _template settings are similar, you can test lengths by taking a screenshot. BlastEm will tell you if this failed.

Another way to tell is by opening the debugger, then entering c or continue into it to make emulation proceed. When you try to log, an error will appear in the debugger window if logging failed.

To fix such cases, you can shorten the filenames in the _template settings by removing some of the % wildcards. Or, simply shorten the ROM's filename itself.

Note: If your new settings don't seem to take hold, it's probably because you've opened BlastEm before and it created a separate blastem.cfg file somewhere else. To remove that, first open BlastEm and go to Settings -> System. You should see an option named "Save config with EXE". Check this option, then close BlastEm and delete the blastem.cfg file that appeared in its folder. (Or, you can edit the options in the other blastem.cfg, if you can find it.)

You can also control where saved games and states go:

save_path $EXEDIR/$ROMNAME

Where $EXEDIR is used it's possible to use .. However, they aren't the same. . means the folder that BlastEm was launched from! This will not match $EXEDIR if you do a complex thing like reuse a cmd window inside your VGM working folder to open BlastEm with cmd options. If that confused you, just stick with $EXEDIR to be safe.

Feel free to experiment with these settings and learn if you're of a mind. But if you just want quick and dirty workable settings, this should suit you, I hope.

Using the Debugger [work in-progress]

There are two ways to open BlastEm's debugger:

• Press u while a game is loaded.
• Use the d command line switch; the debugger will automatically open when a game is loaded.

When the debugger opens, control goes to its window; the main BlastEm window will pause game execution and stop responding to input until you enter c or continue in the debugger. Then the debugger will stop responding to input. You'll must press u again to make it respond.

Both windows "queue" any keystrokes that you perform in them while they're inactive. Otherwise, it's not possible to work with both windows at once. BlastEm is always either in "game mode" or "debugger mode."

Recent (years ago, at the time of writing...) nightlies have streamlined debugger usage. For instance, to print the value inside a register, enter something like this:

print/x [$ff05ec ].b

/x makes the output printed come in (lowercase) hex; it's a format code. [brackets] are needed to access memory. (The space is currently needed due to a parser bug.) .b indicates the address is byte-length.

set [$FFF009 ].b 130

Odd-numbered 68k memory addresses can't be accessed as Wwords. If you don't know what that means, it means you have to specify the length as a byte, as shown above.

To set a value using a hex number, you must prefix that number with 0x:

set [$FFF009 ].b 0xE1
z80 set [$1B88 ] 0x81

Use ? or help in the debugger for a list of commands.

You can hit return/enter without typing any commands to reuse the last command you entered. For fun, use frames 60 and hit return a bunch of times before focus returns to the debugger.

And for a concrete example of using the debugger to log songs, see Using BlastEm's Debugger to Play SMPS Songs.

For those coming from the Sound Hacking/Sega Consoles page

For triggers that say maincpu

Use set in 68k mode. (This is the default mode when you open the debugger; you needn't do anything special to use it unless you've changed the debugger to z80 mode.)

For genesis_snd_z80

Use set in z80 mode. That's done by using the z80 command as shown above.

You can also use z80 by itself to change to Z80 debugging mode; then you can use set directly with z80 numbers. Note that many SMPS games use the trigger address 1c09.

Using Game Genie codes with BlastEm (for now)

Although BlastEm currently lacks Game Genie support, the utility Game Genie Guy can apply codes for you (and unlike other more dated utilities, it does work). For some games, you must include the "Master Code(s)" to override the checksum, or combine GGG with the UCon utility to correct the checksum when you patch (the GGG readme explains how). If GGG doesn't work for your code, try reading the Troubleshooting section of its readme. (Big thanks to Elfor from the BlastEm Discord for this tip.)

The reason some codes may not work with BlastEm is that they change RAM values to a fixed value; that's impossible to do by patching the ROM, and currently impossible in BlastEm because the values you set with set may just change to something else like nothing happened.

So, if your code is not working, another possibility is to create a GSX savestate with the code you want active in a different emulator, like the Gens/GS r7/+ version listed in our Emulators category. (Some codes only work with that emulator's GG, not Kega or Regen. That's because it's more accurate.)

You want to name the state slot_#.gst where # is any number between 0-9. Then, put it where you've configured BlastEm to look for savestates. (With the settings above, that should be in a folder named for the ROM filename.) You can use both .state and GSTs right by each other, but the former is always what BlastEm looks for first - unless you set the default state type to GST.

And if that doesn't work???

As I discovered to my dismay when trying to access the sound test in Garfield: Caught in the Act (as mentioned on TCRF), the above can fail. The states opened fine, but the logs were garbled for some reason! In this special case, though, I managed to use the PAR code in BlastEm by:

1. Resetting
2. Immediately opening the debugger (actually, it has to be slightly after resetting but before the Sega Logo, so blastem -d won't really help; takes a bit of lucky timing but is very repeatable)
3. Using set to apply the PAR code:
   • set [$FFEE20 ] 59
   • set/X [$FFEE20 ] 0x3B (note the omitted leading zeroes)
4. Continuing.

Because the Sega Logo is a "scene"/"level" within the game, and so is the debug menu, I made the game load the latter instead of the former. Trying to set the value after other stuff had already been initialized didn't work. This may not work for you either, but with some ingenuity you might be able to achieve results.

Before you file a bug report concerning a specific game...

It's possible an apparent bug may occur on real Genesis/SCD hardware (which makes the bug "correct behavior"); also, a difference from another emulator could be due to that emulator being inaccurate, not BlastEm. Because of these possibilities, it's most helpful to confirm that the game's bug/inaccuracy does not occur on real hardware, and record proof as such, before bringing a report if you can.

That said, if you're unable to do this, BlastEm's developer prefers you risk being wrong than not report a real bug.

The BlastEm homepage links to the project's issue tracker and lists ways to contact the developer about bugs.