Emulating DOS games (320x200@70hz)

[pakoman]

Hi.

I'm trying GroovyMame to emulate DOS games and the result is very satisfactory, although not as straight forward as DosBox.

Please may anybody help me configuring GM to get pixel perfect progressive resolution at 15 khz?

As most games use 320x200 resolution with doublescan, the VGA outputs something around 640x400 or 740x448 at 70 hz, so GroovyMame tends to select an interlaced resolution.

I'd like to emulate those games with a progressive 15khz resolution like 320x200/224/240 with black borders up and down but using integer divide for the vertical resolution to avoid artifacts, something like 2560x240 but forcing single scan...I hope I'm explaining correctly.

What is the best Groovymame configuration for this? If Mame vertical resolution for DOS machines could be divided by 2 that would do perfectly the trick as it is trivial for super resolutions to scale the horizontal resolution and show vertical resolution pixel perfect with black borders.

Also achieving the 70hz in a 15khz CRT is impossible. What is the best option for this?

Thanks.

[Calamity]

Hi pakoman,

Can you provide an use case (command line, machine, etc.), I'm quite interested in this.

[pakoman]

Hi pakoman,

Can you provide an use case (command line, machine, etc.), I'm quite interested in this.

Sure, even if you want I can send you the CHD I'm using, it's already bootable with several games and Norton Commander to try (about 15 MBs CHD). As far as the BIOS is configured properly, the same CHD can be used with different emulated PCs.

Basically I use these two, the 486 works better but it doesn't run at 100% speed on my computer, and some older games would  run too fast anyway. The 386 gives a Non-Working warning, but so far seems to run fine:

mame64 ct386sx -ramsize 32M -hard1 new.chd
mame64 ct486 -ramsize 32M -hard1 new.chd
mame64 ct486 -ramsize 32M -hard1 new.chd -flop1 win98boot.ima

You can try 386i, at386, pc2386, c386sx16, pc3086, i8530286, ct386sx, apexeni, but I recommend ct386sx and ct486. Ram amount it's not really important.

The cdrom must be configured inside mame, in the 'SLOT' menu, as well as the SoundBlaster or other extra hardware and then the emulated system reseted. However, they're not needed for resolution testing.

You need to configure the BIOS of the emulated computers with the proper hard disk type and parameters, floppy drives, graphics adapter... (I can send you also the NVRAM files to save time) and depending on your Keyboard you may need to change the key in Mame assigned to change Keyboard emulation from full to partial (BLQ DSPL by default).



I guess that when emulating for instance a PC1512 it would be outputting in games 320x200 at 15-16 khz single scan in CGA colors, as those computers used CGA monitors. But we're talking here about VGA.

PS: I'm using windows10 and hd mobility 5650 with super resolutions. I've sent you a PM with the files I'm using.

[Recapnation]

'Sup, Pako.

If forcing a progressive mode of half the lines into GM to subscale vertically the picture without artifacts doesn't work, a way is hardware deinterlacing. Let MAME use the mode of 400/480 lines much like the original hardware did and deinterlace the output by using an RGB interface. If you don't know these, they don't process the picture so no lag is added (a good one I have: http://www.extron.com/product/img-lg/rgb203rxiedid-lg.jpg). Assuming you still don't have a TV set which lets you deinterlace through the service menu, that is.

I don't think you'll get around the 70-Hz issue with a standard 15-kHz CRT, though. How's it using DOS-Box? 60 Hz?

[M_W]

Wait, so are you using CRT_Emudriver, or are you trying to do this with stock drivers? I can't say I've ever used MAME's DOS emulation, but I have successfully gotten 15kHz modes using DOSBox and CRT_Emudriver.

[pakoman]

Recapnation, I know there are hardware solutions and tvs that do the de-interlace thing, but I prefer doing it in software without adding extra stuff. About the 70hz let's rely in GM tricks to make things smooth, however I remember tearing and poor scrolls in most games from the older MsDos era. I remember that Soccer Kid surprised me by then due to the smooth and fast scroll (maybe it was running at 70 fps with vsync while most games didn't seem to care).


M_W
I'm using CRT driver in windows 10 (HD5000).
Years ago I managed to fake a 320x200 res into a 320x240 with black borders and worked fine with DosBox but it was a hassle and I prefer using Mame than DosBox.


The ideal solution for this kind of doublescan resolutions would be that GM allowed to do something like -prescaley 0.5, hopefully Calamity may find it an interesting option and implement it  .

Right now Mame only allows -prescale with a minimum value of 1.


Cheers

[Recapnation]

I'm sure he will find it more than interesting. Take, for instance, MAME's X68000 emulation. Many X68 games were originally line-doubled without an option to run them at 15 kHz for some reason (this computer used a multi-sync monitor). Currently (unless this changed in a very recent version) MAME runs these at their "design" resolution instead of the corresponding double-scan mode which would mimic the original presentation. This is perfect from the [15-kHz] user's perspective (in my opinion), but it goes against accuracy, so I'm sure it will change in the future. Therefore, the only way to display them in "true low-res" again without resorting to hardware solutions will be by halving the vertical res. beforehand. Many cases would benefit from this, indeed, and more importantly, some where the hardware deinterlacing wouldn't help for not being a line-doubled picture:



I thought you actually could achieve that already.


How's MS-DOS emulation status under MAME? Is 70 Hz (68.036862?) really the usual value for these games originally or did it depend on your configuration?

[Calamity]

It all depends on how MAME is currently reporting those BIOS ("DOS") video modes. E.g., mode 13h is 320x200 doublescanned. As long as MAME reports 320x200, GroovyMAME will happily render it as 200p singlescanned (15 kHz). However, if MAME is reporting 400p, then there's certainly a problem, because integer-downscaling is not allowed by design.

[Recapnation]

So integer downscaling is not allowed but non-integer is? How come!?

As long as MAME reports 320x200, GroovyMAME will happily render it as 200p singlescanned (15 kHz).

Which is what happens with X68's "double-scanned" games, I take? It's... curious, the different policies over the same thing you still find in this emulator.

[pakoman]

I've seen so far that Mame always picks doublescanned VGA modes, which is accurate and what the real hardware would do. Boot vertical refresh varies around 55-70hz depending on the emulated machine, this is text mode. I don't know if it is the same during games in graphics mode 13h, mode X or whatever...didn't check refresh rates, but maybe they're not standard for all cards.

Some bizarre workarounds would be install a 15KHz TSR in the emulated machine (don't know Mame behavior by doing that, but if emulation is accurate enough should work!). Or emulate overclocked computers like PC1512, PC1640... that already output 15Khz, but don't support VGA. The Amstrad PC2086 supported VGA and even had some switches to adjust graphics output frequency.

[Recapnation]

I don't know if it is the same during games in graphics mode 13h, mode X or whatever...didn't check refresh rates, but maybe they're not standard for all cards.

If you could check it out with some not-too-obscure games under a typical hardware configuration and let us know here what you get, we may end up learning that it's never 70 Hz, nor even more than ~62, for that matter. If it's indeed 68~70 Hz usually, maybe it's kind of pointless emulating this with a 15-kHz CRT, at least for action games.

15KHz TSR

Did that really exist? VGA and 15 kHz are mutually exclusive, so do you believe that there were an actual way to play VGA games in 15-kHz? (Honest question; never was into DOS and early WIN...)

[pakoman]

15KHz TSR

Did that really exist? VGA and 15 kHz are mutually exclusive, so do you believe that there were an actual way to play VGA games in 15-kHz? (Honest question; never was into DOS and early WIN...)

Not only I believe it, I've already done. Sure they exist and work. Even the ArcadeVga works in MSDOS out of the box at 15 KHz with games. The VGA card is capable of outputting 15khz resolutions, a standard VGA monitor isn't.

VGA games used pretty much the same resolution as arcade games, although doublescanned to work with 31KHz VGA monitors.

[Recapnation]

I meant "in a non-hacky way" and "at its moment". It sounds unlikely that MAME will ever report single-scan/15-kHz if that only comes from a hacked BIOS. The multi-sync PC-2086 you mentioned, didn't let you switch to 15-kHz when you're in VGA mode, did it?

[Calamity]

Ok, it turns out it's not too hard to display CGA/VGA 200-lines modes as 15 kHz single-scanned modes. Unfortunately you need to force some options manually, so it'll only look good while in the game's graphics mode. DOS text screens will look crappy.

All what you need to do is:

1.- Add a new mode 2560x200@60
2.- Run: mame64 ct386sx -ramsize 32M -hard1 new.chd - r 2560x200 -ues -nouesx -nofilter


Optionally, if your monitor supports it, you can extend your crt_range to reach 70 Hz:

crt_range0 15625-16200, 49.50-71.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.024, 0, 0, 192, 288, 448, 576

(I wouldn't bother anyway, most PC games didn't care about vsync at the time. I've tried it in my PVM and it syncs correctly at 70.8 Hz but there's some geometry distortion).

In my tests, this produces perfectly clean scanlines for both CGA and VGA 200-lines modes. So far I've tried Golden Axe, Side Arms, Goody, Gauntlet, etc. Let me know if it works for you.

[Recapnation]

Sounded really weird you couldn't force it currently. How's the syntax for "-nouesx" in machinename.ini (or you can't set that there)?

[pakoman]

Ok, it turns out it's not too hard to display CGA/VGA 200-lines modes as 15 kHz single-scanned modes. Unfortunately you need to force some options manually, so it'll only look good while in the game's graphics mode. DOS text screens will look crappy.

All what you need to do is:

1.- Add a new mode 2560x200@60
2.- Run: mame64 ct386sx -ramsize 32M -hard1 new.chd - r 2560x200 -ues -nouesx -nofilter


Optionally, if your monitor supports it, you can extend your crt_range to reach 70 Hz:

crt_range0 15625-16200, 49.50-71.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.024, 0, 0, 192, 288, 448, 576

(I wouldn't bother anyway, most PC games didn't care about vsync at the time. I've tried it in my PVM and it syncs correctly at 70.8 Hz but there's some geometry distortion).

In my tests, this produces perfectly clean scanlines for both CGA and VGA 200-lines modes. So far I've tried Golden Axe, Side Arms, Goody, Gauntlet, etc. Let me know if it works for you.

Thanks for your time looking into it. That solution works fine for 200 lines resolutions, I had to limit the max hz to 64, it's the closest I can get to 70 hz. Oddly enough my tv supports 224 lines at 65hz, but gets out of sync with 200 lines. I added 2560x200 and 2560x224 to the system.

Maybe it isnŽt worth the effort in going further than that, and if a specific game uses 224 or 240 lines, just choose the specific resolution. Although ideally having the V res would be the optimal solution for this doublescan scenario.

What is this for? It seems to apply some filtering only on text modes, but has no effect in game at all.
-ues -nouesx -nofilter

BTW Have you tried Rastan  (Rastan Ega)? It seems to use a different resolution than mode 13h while in-game and report weird number of lines depending on the used method or even an interlaced display while the intro screen is progressive, leaves the energy bar out of the screen...


In the other hand, in the meantime I tried some VGA 15khz TSRs and worked fine with MAME!    Depending on which one I got different hz and sizes of the black borders. Even one of them worked at 120hz so emulation was running at half speed at 2560x240x60. But Mame reported 200 lines and Switchres chose a progressive mode accordingly.


And about the 70hz, I don't remember old games to have a very smooth scroll and even had screen tearing anyway, but not matching the refresh may produce another tearing while scrolling (2! lol) and even choppier scroll. Is there any triple buffer option or similar configuration to mitigate this? (apart from trying to get the closest possible to 70 hz).



Recap, 15 khz TSR existed by the time, they are very simple programs, but information was not as universal as nowadays and by then the only I knew about Khz and so was that my VGA monitor didn't show black-lines while my friends' EGA or CGA monitors showed with the same game (I know now the reason, not then!).
The first time I tried this with MSDOS was with Raine and MAME that both had specific options in the DOS versions to display 15KHz, and also the Genecyst emulator with a TSR. Got all the info through internet dial-up. Even AdvanceMame has some generic tools to display VGA and VESA modes for MsDOS at 15 khz and even some designers used 15khz monitors connected to specific VGA cards.

The PC2086 was the first PC we had at home but I didn't dare to change the switches afraid of breaking something. I knew about their function not so long ago.

Most games use mode 13h, thus 320x200x70. Although nobody seemed to care about the *70* in PCs by then, while console games had a smooth scroll.

[Recapnation]

What is this for? It seems to apply some filtering only on text modes, but has no effect in game at all.
-ues -nouesx -nofilter

Uneven stretching? I guess it's thanks to that that you get rid of the lines corresponding to one of the "scans", even if it's not "stretching" but "shrinking" in this case. You don't want that in the horizontal dimension, hence the -nouesx. And of course, you don't want any filter in the process.

15khz monitors connected to specific VGA cards.

Would love to hear more about that. Even if I generally consider MS-DOS games utter ---steaming pile of meadow muffin--- as you know, documenting the [official/commercial] solutions in history for the line-doubled graphics issue is still a pending subject. I always thought that not all the IBM-PC users could be happy with legos back in the day.

[Calamity]

-ues (unevenstretch 1): This one is required so fractional stretching is forced. We need to apply a fractional scale factor of 0.5 to the vertical axis. Integer scaling is not possible since the minimum possible integer factor is 1. The trick to avoid scaling artifacts is to choose a resolution which height is the exact half of 400. The width is not a problem because we have a superwide resolution.

-nouesx (unevestretchx 0): This should only be required by v0.176, to avoid -unevenstretchx to be automatically enabled. Starting from 0.177 it shouldn't be required explicitely. (unevenstretchx applies fractional scaling to x axis and integer scaling to y axis, which is not what we want!).

I recommend using -nochangeres too, as constant resolution changes make the emulation too slow.

You can use -triplebuffer to avoid tearing. If the -autosync option is enabled, -triplebuffer should be automatically applied if the difference between the target refresh (70 Hz) and the refresh that's actually achieved (65 Hz) is beyond -syncrefresh_tolerance (2.0 Hz by deffect).

----

I couldn't resist mentioning I also coded a TSR green screen emulator with hardware scanlines back in the day: http://www.abadiadelcrimen.com/verde.html

It'd be nice to check if it works 

[keropi]

^ wow verde... I'll check it out on my dos pc!

[pakoman]

-ues (unevenstretch 1): This one is required so fractional stretching is forced. We need to apply a fractional scale factor of 0.5 to the vertical axis. Integer scaling is not possible since the minimum possible integer factor is 1. The trick to avoid scaling artifacts is to choose a resolution which height is the exact half of 400. The width is not a problem because we have a superwide resolution.

-nouesx (unevestretchx 0): This should only be required by v0.176, to avoid -unevenstretchx to be automatically enabled. Starting from 0.177 it shouldn't be required explicitely. (unevenstretchx applies fractional scaling to x axis and integer scaling to y axis, which is not what we want!).

I recommend using -nochangeres too, as constant resolution changes make the emulation too slow.

You can use -triplebuffer to avoid tearing. If the -autosync option is enabled, -triplebuffer should be automatically applied if the difference between the target refresh (70 Hz) and the refresh that's actually achieved (65 Hz) is beyond -syncrefresh_tolerance (2.0 Hz by deffect).

----

I couldn't resist mentioning I also coded a TSR green screen emulator with hardware scanlines back in the day: http://www.abadiadelcrimen.com/verde.html

It'd be nice to check if it works 

Thanks for the explanation, in my setup (GM 0.177 windows super resolutions) seems that the unevenstretch 0.5 is not needed, as GM is doing it by default when using a 200 lines resolution to show a 400 lines image.

I tested "verde" and in works fine with mame   IŽll post a pic when I have time. Are you the author of the Abadia del Crimen remake?

[pakoman]

Some random pics, pixel perfect, progressive and interlaced of 'verde' TSR:

[Calamity]

Looks so cool, thanks!

Are you the author of the Abadia del Crimen remake?

Yes.