MiSTer FPGA Forum

Bit of a shot in the dark but any video mode recommendations for AO486 or X68000 cores on a 15khz Sony BVM?

I've tried a load of recommendations already posted on the forum but no joy.

My video chain is HDMI out -> HDMI to VGA Adapter -> VGA to BNC cable straight into the back of the BVM monitor.

Thanks!
John

Neither of those cores are 15khz natively so unfortunately won’t work. X68000 has switchable 15khz modes that you can get at once you’re into a game that supports.

Thanks for responding. I understand that. But in theory it should be possible use the vga scaler to downscale the 31khz signal to a 15khz compatible signal.

The modelines from here work, but if you're using Direct Video you'd need to add an adapter to your chain which does H Sync stripping combining, like one of these VGA2SCART converters.

I guess so. But that would be at the expense of latency and image quality.

No it wouldn't, these converters do not add lag and display is 1:1.

Assuming you got your video setup working with other cores you shouldn't need any additional converters. Just some kind of custom video mode like those provided above.

FoxbatStargazer wrote: ↑Sun Jul 03, 2022 11:50 am Assuming you got your video setup working with other cores you shouldn't need any additional converters. Just some kind of custom video mode like those provided above.

https://github.com/MiSTer-devel/Main_Mi ... 1133949156

Interesting, so the takeaway seems to be that csync=1 doesn't work with the scaler, only direct video. So you need a combiner to fix.

You might also need to pick a wider resolution to get the pixel clock up to snuff, depending on your converter. So something like 1440 wide or even 2048 wide. Many of the custom modes just assume analog I/O board where such isn't needed.

akeley wrote: ↑Sun Jul 03, 2022 9:47 am The modelines from here work, but if you're using Direct Video you'd need to add an adapter to your chain which does H Sync stripping combining, like one of these VGA2SCART converters.

Thanks @akeley. That makes perfect sense as I previously had these cores working with custom mode lines via an IO board and recently switched to HDMI / direct video for the enhanced colours.

So I should either use the IO board for these cores or add a VGA2SCART into the chain. The later option shouldn't add any noticeable lag - is that correct?

zoopster wrote: ↑Sun Jul 03, 2022 12:46 pm The later option shouldn't add any noticeable lag - is that correct?

Not that I know of, at least the one from Arcadeforge (UMSA) I'd been using before I got the I/O board. Retroupgrades also says there is "Zero lag – lag of less than 0.01ms (effectively ZERO)" about theirs.

I can vouch that the Arcadeforge one definitely does the H Sync trick and so modelines (and those pesky cores which previoulsy didn't work) work, been using it with AG6200 based HDMI-VGA adapter. Retroupgrades one I heard about on the forums somewhere. Antoniovillena's I can't vouch for 100%, maybe it does. For these last two I'd ask the sellers directly first, if you think of buying.

Also, perhaps this H Sync combining can be accomplished in some other way (modding the adapter maybe?). I think it's kinda accidental that it does in these aforementioned adapters (eg I've been using the UMSA for my crtemudriver PC, that's its primary purpose, and only tried it with MiSTer on a whim).

EDIT: I'm also not 100% sure this chain would work with PVM/BVM since they might handle syncs differently than consumer sets. I think I've tried it once on my PVM and the image wasn't too great, but then the SCART-BNC adapter I had at the time wasn't too good either. I'm getting a couple of new ones this week, might try it again then.

Let us know how you get on. I just ordered the Retro upgrades adapter to try it out.

dazzer69 wrote: ↑Sun Jul 03, 2022 9:25 am Neither of those cores are 15khz natively so unfortunately won’t work. X68000 has switchable 15khz modes that you can get at once you’re into a game that supports.

OP, excuse the offtopic..

@dazzer69 the hard part is mapping the corresponding x68k key to the pc keyboard. I know Star Force has a native 15khz mode when pressing the HELP key on a x68k keyboard.. but i have no idea where is the HELP key mapped in the pc one.

I’ve not been brave enough to try X68000 on CRT tbh.

_javi_ wrote: ↑Sun Jul 03, 2022 5:20 pm but i have no idea where is the HELP key mapped in the pc one.

Apparently it's sort of possible - press left mouse button before launching a game (on DOS screen or thereabouts). Then a little keyboard overlay will appear. You can use mouse cursor to choose and click keys on it. I don't have my VGA monitor connected atm to try it out but maybe it could be possible to use this to launch at least some games in true 15khz, the ones that need some keys pressed during startup to switch to 15khz.

The AO486 is doing VGA, which is fundamentally a 30KHz-ish signal. Any method you find to display that on a 15KHz display is going to be sharply impaired. You may be able to monkey around and get it kinda working, but it's never going to be very good, and it's not something that real PC hardware would have done.

That monitor should be excellent as an output device for the Minimig core, probably the ST core in color mode, and probably most of the 8-bits and a lot of the earlier arcade displays. But even if you can figure out how to downsample the more advanced 30KHz signals, you probably won't be thrilled with the result.

If you can source one, a 30KHz+ multisync that accepts 15KHz signals would work a lot better.

Malor wrote: ↑Sun Jul 03, 2022 11:48 pmYou may be able to monkey around and get it kinda working, but it's never going to be very good

"Monkey around?" Sure, why not (thanks, @thorr)



I'll leave it to viewers to decide whether this result is "never going to be very good" or "sharply impaired". For me personally this ability is one of the best things about this core, since I never liked the VGA blockiness/sharpness in most games. I do have several VGA CRT monitors and use them too sometimes, but since these modelines appeared I spend approx 80% of my ao486 time in this mode. The image is scaled 1:1 in games, looks absolutely stunning, and should work for most DOS titles from the 320x200 era.

Your jibe that "it's not something that real PC hardware would have done." is also nonsensical since of course it did, with CGA first and later on assorted TV-Out cards, but more importantly because MiSTer is all about doing things which old hardware wouldn't have done, chief example being HDMI output. Yet, I don't see anybody complaining about that.

The same modelines from ao486 can be used for PC-8801, also with great results. X68000 is much more trickier and not always as good, due to multum of weird resolutons used and need for separate modelines (more work is needed on that). But it's still worth trying out and can work very well in some games.

That's better than I expected, but all the details are large there, with text the size of Kansas. If you try to run things with much detail, it'll probably be pretty blurry. Adventure games that are more pixel-hunty than MI2 could be problematic, for instance; the King's Quest games might be harder than they normally would be.

And yes, you could hook up a TV or composite monitor to a CGA card, but CGA was a 15KHz signal, and even then was really impaired in most cases. You did get the 'artifact color' mode that looked a lot better than a TTL monitor, but you really didn't want to try to run a word processor that way.

VGA is fundamentally a 30KHz signal, and you will always get worse results from trying to jam it into half the bandwidth.

Most VGA DOS games are 320x200, including the vast majority of point n clicks. Something about the memory structure made that convenient for a while. On a VGA monitor they are just getting line doubled to 400p, so it "fundamentally" does not matter much. You can easily fit 200p into standard definition if you just get the downscaling set up so that every pixel of game art is represented 1:1. After that it's purely a matter of taste whether you find scanlines offensive or not.

That said it is preferable to hit 70hz for 200p if you can, which can be tricky on SD displays. I managed to get an Atari SC1224 to do that, I would bet with the right modelines some professional monitors could probably sync to 70hz as well.

Malor wrote: ↑Mon Jul 04, 2022 10:57 am

If you try to run things with much detail, it'll probably be pretty blurry. Adventure games that are more pixel-hunty than MI2 could be problematic, for instance; the King's Quest games might be harder than they normally would be.

I'm not sure why you continue with this silly derail, since you clearly have no first hand experience with the subject and are now inventing absurd arguments just for the sake of it. Personal preference is perfectly fine - if you don't like how it looks, then so be it (though since you have never tried it yourself it does not matter much anyway) but nobody forces you to use it.

Some other people are interested in this though, and trying to spread misinformation here based on pure speculation could constitute trolling at this point. So, once again, the real image is in no way impaired, blurry, too big (lol), doesn't cause problems in adventure games, or any other such guff. The lack of 70hz might cause some hitches in action games but I'm not really seeing it myself (plus you can try this modeline from FoxbatStargazer). And many games from this era were not written just for PC, but also available on Amiga/ST, so using 15kHz is perfectly natural.

Anyway, I'm not going to argue with you any further since it just generates noise in this thread. But, it's a good excuse to post more photos of ao486 in all its 15kHz glory, so at least there's that

Note to the curious: it's extremely hard to capture CRT image correctly, and I haven't post-processed these images so some colours and details might be off (and the images are best viewed full-size) - but you can take my word for it that it looks even better live. In any case, you can always try it out for yourself if you have a 15kHz set: all it takes is copy-pasting a few lines into your config.