Recommend X68000 settings for VGA PC CRT (31 khz)

[zoopster]

Hi,

I'm connecting my MiSTer via a HDMI to VGA adapter to a PC CRT (Philips Brilliance 201P) and looking for recommend settings for the X68000 core. I've tried a few settings in the forum but most of them are for 15khz CRTs. I've been testing with video mode 1 (1 - 1024x768@60).

Few questions specific to X68000 core:

- Should direct_video be enabled
- Should forced_scandoubler be enabled
- Should vga_scaler be enabled
- Recommendation on vsync_adjust setting
- Recommentation on vscale_mode=1

Thanks!

[FoxbatStargazer]

I think vga_scaler=0 and crucially, forced_scandoubler=0 work right out of the box on VGA monitor. Text prompt and most games should default to 31khz. Of course you probably have forced_scandoubler=1 for most cores so you would need a core-specific INI section (is it [X86000] ?)

With vga_scaler you can make your resolution whatever you want and not have to worry about the game's actual resolution. None of that is very particular the X86000 core though.

[zoopster]

Thanks @foxbatstargazer. I agree - need to start with stripped back video settings and go from there. What's weird is that I'm seeing a lot of video signal interference specifically with the X68000 core. Anyway some more experimentation is needed.

[akeley]

X68000 is really pretty wild when it comes to video_output. It uses 3 frequencies and a heap of different resolutions. It's also unclear if the core can handle them all natively at the moment, and there are might be also glitches resulting from bugs. So that's something to consider. Perhaps you'd need a few modelines to handle all the variations.

I would've thought that at least desktop should display ok - I'm pretty sure it is 31kHz (I've only tried it briefly on VGA and don't remember how it was though. Might try it next time I'm on my VGA monitor.)

[zoopster]

After some experimentation these settings provide the best results across both 31khz and 15khz modes in the X68000 core on the 31khz PC CRT monitor:

[X68000]
forced_scandoubler=0 ; set to 1 to run scandoubler on VGA output always (depends on core).
vga_scaler=0 ; set to 1 to connect VGA to scaler output.
vscale_mode=0 ; 0 - scale to fit the screen height.
direct_video=0 ; 1 - enable core video timing over HDMI, use only with VGA converters.
video_mode=1
vsync_adjust=1

Only downside is that the text in the X68000 CLI is distorted. Interestingly, the 15khz signal also shows on my Sony BVM which is connected via the analog board.

[Wave]

I'm evaluating if I should get a 31Khz screen (VGA monitor) for various computer cores, including X68000.

One question I have is, say I used zoopster's settings in the prior post (thank you for sharing, btw!) with a VGA monitor connected to the analog I/O board. If an X68000 game switched to 240p, wouldn't the VGA monitor go out of sync? I'd at least have to have a second profile with forced_scandoubler=1 for that scenario, right? (And ofc it wouldn't look authentic then, missing scanlines.)

(Off-topic but bonus question: Is there a list anywhere of cores that support / need 31Khz? AO486 obviously, but beyond that...)

[akeley]

There is a list but it's severely outdated and can be misleading (eg Atari ST or Apple II does not need VGA nor is it their "native" resolution)

In practice the cores that would benefit most from the VGA monitor atm would be MacPlus, Acorn Archimedes, PC8801 and X68000, maybe Amstrad PCW too. Some of them do 15kHz thou, either natively or via modelines.

Some lesser cores which might benefit could be the ones marked "No" on this 15kHz compatibility list.

[zoopster]

I'd strongly recommend getting a high quality PC CRT for cores that support 31lhz video modes. Especially, X68000, Amiga (RTG modes), AO486 and Archimedes cores.

In the end I purchased an additional MiSTer just for my PC CRT. The recent changes to MiSTer main to support cvt=CVT timing are a game changer for older PC CRTs that can support 1200p and 1400p modes. I'm now playing vertical arcade games at these higher resolutions on the Philips Brilliance 21" PC CRT and they look great.

My own experience was that the "15khz" 240p modes on the X68000 core still showed on the PC-CRT but your mileage may vary based on the ini settings. The scanline settings look much better in 240p modes on the PC CRT than say 31khz modes (which would have traditionally shown very thin scanlines).

[FoxbatStargazer]

Finally got around to trying X68000 (from main) with a VGA monitor. So I tried feeding it original resolution/refresh over the VGA port, no scandoubler. It works but I'm getting a subtle shimmer, that looks like tiny waves on vertical lines. Kind of have to get close to see it clearly, but you can see that the DOS? text feels unstable at a distance. The same monitor is rock-solid using the scaler in a variety of cores even at 1440p, including this one. This seems to apply to any resolution over 30khz (monitor will obviously have trouble with lower....)

[jd213]

My Mitsubishi PC CRT doesn't like direct analog from the X68000 core either, I think the distortion is similar to what you're describing except it's VERY pronounced and pretty much unusable.

Same thing happens with linedoubled R-Type (Japan) but not R-Type (World) for some reason. WIll need to try more cores.

[FoxbatStargazer]

My Mitsubishi PC CRT doesn't like direct analog from the X68000 core either, I think the distortion is similar to what you're describing except it's VERY pronounced and pretty much unusable.

Same thing happens with linedoubled R-Type (Japan) but not R-Type (World) for some reason. WIll need to try more cores.

Linedoubled Lynx had the same issue, dunno if it was ever fixed.

I also had trouble getting 15khz direct analog out working with a 15khz monitor. Even stuff like final fight, the screen just keeps rolling. Needed to use the scaler to make something stable.

[jd213]

My Mitsubishi PC CRT doesn't like direct analog from the X68000 core either, I think the distortion is similar to what you're describing except it's VERY pronounced and pretty much unusable.

Same thing happens with linedoubled R-Type (Japan) but not R-Type (World) for some reason. WIll need to try more cores.

Apparently this was caused by the Japan version being set to 57 Hz instead of the original 55 Hz. It works fine with 55 Hz, even though 57 Hz on the Cave cores doesn't seem to cause any issues.

Was also pleased that my consumer Trinitron displays 55 Hz over S-Video just fine, wasn't expecting it to like a refresh rate that's halfway between PAL and NTSC.

[jd213]

My Mitsubishi PC CRT doesn't like direct analog from the X68000 core either, I think the distortion is similar to what you're describing except it's VERY pronounced and pretty much unusable.

I thought I'd give this another try, turns out that most of the distortion was because I didn't think to turn the scandoubler off.

Non-linedoubled output on my PC CRT is still jittery, but not too bad. Tried direct video over HDMI with an HDMI>VGA adapter, but no improvements.

I guess it's just another bug with the core that needs fixing, hopefully they will get looked at eventually. Would be willing to see if I could do something about it, but I have little programming experience and my job keeps me pretty busy as it is.

[ron]

The issue for this core, as per many others is this:

issueforcores.png (11.55 KiB) Viewed 10279 times

It not only affects the X68000, but a few cores that are not working or have lost video since the last firmware and framework update

The only way is rollback to the previous release of MiSTer.

Why ?