Hey Guys, Today I started on the Adlib support for my Lemmings emulator and after googling a bit for details remembered I had an old Sound Blaster development kit. Even though I only needed the bit about the timers and status register (because I'm using a port of Robson Cozendey's OPL emulator) I …

Thanks Japael, The reason I ask is that in the emulator I'm writing I had working as follows: 1. Wait till the end of display area (because I need to see any palette switches before passing everything to opengl shader) 2. At the end of the display area draw the screen - and here I was using whatever …

amadeus777999 wrote: Took the machine around 280 seconds a 4 minutes 40 seconds. Thanks - closer to what the emulators are doing than what it should be 😀

Hmm and what about the other modes, e.g. for tandy? My emulator doesn't support all these modes so it's a bit hard for me to say for sure, but I just tried running every different mode in dosbox debugger and all report 320x200 and ~70Hz and in all cases 1 game minute = 73 real seconds. Given that …

I thought I read somewhere that the VGA's CRTC latches the start address register at the start of vertical retrace but I can't find that reference any more - anyone know for sure? ie: if the start address is changed immediately after vertical retrace will it affect the frame that's about to be drawn …

Also, I find it interesting that Lemmings actually rewrites the palette itself. I wondered about that too. Even just rewriting the palette map in the attribute controller I would have thought would be simpler. For more info, see my blogpost on 1991 Donut here: https://scalibq.wordpress.com/2013/11/ …

Could it be that originally the graphics mode for lemmings was 43 Hz interlaced? This would be 86 retraces/s. Interesting idea - possibly I suppose, although the game is definitely selecting video mode 0x0D which is 320x200 @ 70Hz (according to this ) and I don't think it's tweaking any of the CRTC …

FWIW, I got this working nicely in my emulator now. It's a subtle improvement over the non-palette switching version but I think worth the extra bit of effort:

oeuvre wrote: Trying it on a Dell Optiplex GX1 with MS-DOS 6.22, Pentium II 350MHz, 256MB RAM. Bit oeuvrekill but hopefully it helps. Elapsed time was 4:50 static- wrote: Seeing 4:52 on my Pentium II 400MHz in REAL DOS 7.1. Thank you. Pretty sure we can say this was a bug (or weird design) of the …

Is it 4 minutes for stage 1 or 3 minutes? My copy starts at 3-00 on the timer. The file name is also VGALEMM2.EXE (not VGALEMMI as said above). Are there different versions of this game? Not sure but note this is Oh No More Lemmings, not the first Lemmings. The first level is called "Down and Out …

I'll give it a try too, I've got it on a 386DX and a P233MMX so it might be useful to see if they give the same result. Thanks BTW please please please call your emulator "Lemulator." Just saying. In my head I've been calling it "The Lemulator" but the program itself is just called "WinLemmi.exe" - …

Awesome - thank you.

Hey All, (Not sure if this is the right place to post this but seemed the best choice...) I'm working on a simple DOS emulator with the goal to run "Oh No! More Lemmings" for DOS as well as possible on modern Windows. What I've noticed however is that the timing seems off - both in my emulator and …

For anyone who's interested in the details on how this is done, I did some reverse engineering. There are two places where this is used in Lemmings - first on the level intro screen and second in the game itself. Each uses a slightly different approach. Level Intro Screen https://www.dropbox.com/s/ …

Thanks @xjas - nice to see other examples of this and very cool that it was done with CGA too!

I'd say pretty common to lock on to vertical rate and update palette while drawing. Bart vs Space Mutants might do the same. ok cool. I've never seen this described anywhere before. Thanks. IIRC, when VGA is selected, it's in EGA graphics mode but and switching the EGA palette entries, but in EGA …

I think I figured this out. Looks like after detecting the vertical retrace it's setting up the programmable interval timer to raise an interrupt at the required scan line - at which point it reprograms the palette. Anyone know if this was a common technique?

Hey All, First post here! I've been working on a simple DOS emulator - mainly as a learning exercise with the goal to build just enough to run the DOS version of "Oh No, more Lemmings". It's written in C# with an OpenGL shader to render the VGA frame buffer and seems to be working quite well so far. …