VGA Output, Scalers, and CRTs

[deepthaw]

Per this issue: https://github.com/MiSTer-devel/ao486_MiSTer/issues/6

It looks like VGA output is only supported if it goes through the scaler. This means no way to have the monitor itself match the resolution of whatever software is running. This is really only important to people like me who are trying to get it working on a real CRT. The benefit of a CRT for me is that it'll natively display whatever resolution the game originally ran at, which is fantastic to avoid scaling artifacts. Using the scaler means the CRT is running at a fixed resolution, and the output is scaled to match.

In previous releases of the core, I was able to use native VGA, but the image was shaky and had sync problems, which increasing the core speed would improve (but not completely solve.) The latest core no longer displays anything over VGA unless I use a scaler.

I can understand why, since the vast majority of people are using modern monitors, and apparently the VGA timings are really trick. Still, I'd love to see true VGA output come to the core eventually.

Speaking of scalers, I've been playing with some custom resolutions to get it to work the best. I've noticed that even when the scaler is working at a resolution that should match up to the "native" output (either 1:1 or 2:1), there are still scaling artifacts. For instance, a custom mode of 720x400 looks perfect for text, except for a vertical line missing every so often.

o9Unhih.jpg (256.58 KiB) Viewed 18315 times

(look at the first "O" in the directory name.)

640x400 looks good in Doom (320x200) but there are still scaling artifacts (I have to look a bit to see them, since the nature of Doom's graphics hide them. They're most obvious in text.)

Here's my ini lines for 640x400 and 720x400 if anybody else wants to play with them.

video_mode=640,24,96,40,400,9,2,39,25175; 640x400 (Good for 320x200 games)
video_mode=720,32,120,32,400,7,6,8,32470; 720x400 (Good for text)

I imagine 320x240 games (Epic Pinball, I believe) would work best with 640x480.

I plan on continuing to experiment with what looks best on a CRT but right now I think a modern display is actually better suited due to the wild number of resolutions you may run into (720x400 for text, 320x200 and 320x240 for VGA games, 640x480 and 800x600 for Windows, etc.) and the ability of the scaler to look better working at 1080p.

(I care about text because I still BBS. ANSI art on a CRT is a thing of beauty.)

[Caldor]

Yeah, I have been hoping to do this as well... with the scaler it seems a bit pointless to use a CRT monitor I think. I did get VGA working with the variable refresh rate, but anything using SVGA would not work at all. But that was Cache 24 or something last time I tried using a CRT.

[deepthaw]

Yeah, I have been hoping to do this as well... with the scaler it seems a bit pointless to use a CRT monitor I think. I did get VGA working with the variable refresh rate, but anything using SVGA would not work at all. But that was Cache 24 or something last time I tried using a CRT.

Yeah - I love using my MiSTer with CRTs. The lack of shimmering during scrolling, the native resolution, etc. is beautiful. While I imagine there's a small number of people using it with CRT televisions, an even smaller number of people using it with VGA Monitors with scandoubling, there's probably only a handful of us trying to use it in this particular use case.

(My VGA Monitor with scandoubling is stunning for console games, btw. It's like having a PVM except not expensive. And it does 50Hz for Minimig.)

[Caldor]

Yeah, I have been hoping to do this as well... with the scaler it seems a bit pointless to use a CRT monitor I think. I did get VGA working with the variable refresh rate, but anything using SVGA would not work at all. But that was Cache 24 or something last time I tried using a CRT.

Yeah - I love using my MiSTer with CRTs. The lack of shimmering during scrolling, the native resolution, etc. is beautiful. While I imagine there's a small number of people using it with CRT televisions, an even smaller number of people using it with VGA Monitors with scandoubling, there's probably only a handful of us trying to use it in this particular use case.

(My VGA Monitor with scandoubling is stunning for console games, btw. It's like having a PVM except not expensive.)

Its one of the real benefits of using an FPGA for these systems I think... but a lot have happened with the AO486 core over the last month or so with the cache updates. Its amazing how capable the developers are, and of course its better to have a working VGA output than no VGA output. But I do hope to see it working in the future.

I have been looking a bit into FPGA development, and... well it does not seem much like the type of coding I usually do, but I think I will keep experimenting a bit and see if maybe I can get some simple stuff to work, to help me figure out the logic and process of it. I tried looking into how to add more drives f.ex., but... right now its using the primary of two controllers to get the two disks that are supporting, so it takes a bit more to get the slave drives to work for those two controllers. Also it seems right now these HDD controllers are somehow using the floppy controller, which I think might be why benchmark DOS tools do not recognize them as HDDs to do benchmarks for. Games do not seem to care though, as they just seem to check for drive letters and space available. It might be why there are some issues in Windows though.

Overall, I do not feel like I am close to being able to do something useful for FPGA cores yet.

[jrronimo]

Yeah, I have been hoping to do this as well... with the scaler it seems a bit pointless to use a CRT monitor I think. I did get VGA working with the variable refresh rate, but anything using SVGA would not work at all. But that was Cache 24 or something last time I tried using a CRT.

Yeah - I love using my MiSTer with CRTs. The lack of shimmering during scrolling, the native resolution, etc. is beautiful. While I imagine there's a small number of people using it with CRT televisions, an even smaller number of people using it with VGA Monitors with scandoubling, there's probably only a handful of us trying to use it in this particular use case.

(My VGA Monitor with scandoubling is stunning for console games, btw. It's like having a PVM except not expensive. And it does 50Hz for Minimig.)

I'm with you: I intend to use my MiSTer with a VGA CRT for computers and with Component input TVs for consoles. I have one of the HDMI to VGA adapters (rather than an IO board) and the last time I tried using it with my VGA CRT, I couldn't get the video to be quite right. I'd really love for there to be support for native resolutions. I bet that my HDMI to VGA adapter is going to affect that quite a bit, though...

For me, there's nothing like the warm glow of a CRT (except for how it compares to an LCD on my power bill. )

[thorr]

I am using a CRT 22" Mitusbishi Diamondtron SVGA monitor exclusively. I am using Cache 43 successfully at 90 MHz. The image shakes a little bit, but I can live with it. It broke with the official core in Doom, but it still works with Second Reality. I think it depends on which video mode is displayed whether it is out of sync or not. For now, I will just use Cache 43 as it works well enough.

[akeley]

I have yet to try this core myself, but if it's not working properly with VGA monitors then it's of no use for me.

Good catch with the scaling artifacts deepthaw (playing PoR, one of my favourite games ever is added bonus). It reminds me a bit of the Dosbox pixel quagmire. Guess I won't be getting rid of my DOS PC anytime soon yet.

[deepthaw]

I have yet to try this core myself, but if it's not working properly with VGA monitors then it's of no use for me.

Good catch with the scaling artifacts deepthaw (playing PoR, one of my favourite games ever is added bonus). It reminds me a bit of the Dosbox pixel quagmire. Guess I won't be getting rid of my DOS PC anytime soon yet.

The scaling artifacts aren't as bad as they could be. They're very noticeable in text mode stuff, much less so in games. Pool of Radiance looks and runs well for the brief time I was able to test it.

[akeley]

Maybe so, but the idea behind using FPGA (at least the way I see it) is aiming for 1:1, authentic reproduction of the original hardware. If this core produces display artifacts then I might as well stick with other solutions.

[ash2fpga]

Ahhh, I was about to pull the trigger on a de10 nano dedicated for computer cores, hooked up to a PC monitor.

I wonder if part of it is a limitation on when the main mister core will perform a resolution change? Or can a computer core (if programmed to do so), change resolution at runtime (the resolution the monitor sees, not [just] what the mister scaler sees)?

[NightShadowPT]

Ahhh, I was about to pull the trigger on a de10 nano dedicated for computer cores, hooked up to a PC monitor.

Don't let this stop you. The experience is amazing...

[Caldor]

Ahhh, I was about to pull the trigger on a de10 nano dedicated for computer cores, hooked up to a PC monitor.

Don't let this stop you. The experience is amazing...

Yeah.... RetroPie is pretty great, but I prefer the MiSTer. There are a lot of useful scripts, but would be nice with scripts that did a setup capable of working with CRT monitors Right now I just have two scripts for graphics setup. One is called "Optimal" and another is called "compatible" and I have no idea what each of them do. But there is a nice "ini" script that seems to support most of the ini file options the MiSTer has.

Its pretty certain I believe that the MiSTer will support CRT at some point, and until then... well its still more power efficent that a full size PC and probabably also the Raspberry Pi since it uses emulation, and its also smaller than PCs and laptops making it more portable.

The better power efficiency is great for making it more portable also. But portable and CRT probably does not go together well... unless maybe doing something like the SX64?

And while the VGA support is not as great as the original hardware, it is there and working with the right settings. It just depends quite a bit on the cores. I do have a 15khz CRT and a 15khz LCD, so I guess that could be used for a few things. My 15khz LCD is some cheap crap though. Cost about... 70 dollars? I think it was less even. The problem is it flickers like crazy at ANY resolution and setting.

The MiSTer overall is pretty amazing with how much it supports, especially all the arcade cores. Being this open source and so on, makes it the FPGA with the most potential by far I think. But on top of that it without doubt supports the most systems and in several cases I think it even supports some of the systems better than f.ex. Analogue and the Turbo Chameleon 64. But I will have to do some tests to see if that is the case. There are pros and cons with each of them for sure.

[SuperBabyHix]

@deepthaw I don't have a CRT to test, but I was wondering if using a higher horizontal resolution (1440x400) in conjunction with one of the scaler filters that only blur on the horizontal axis (e.g. gausionsharp_NN_6) would at least let you get desirable results for the most commonly used resolution an minimize scaling artifacts. I have not tried this on the Mister before in any way, so I'm not entirely sure the aspect ratio correction would work, but I have done this with a PC emulation setup and a 15Khz CRT before and it looked very good.

[deepthaw]

@deepthaw I don't have a CRT to test, but I was wondering if using a higher horizontal resolution (1440x400) in conjunction with one of the scaler filters that only blur on the horizontal axis (e.g. gausionsharp_NN_6) would at least let you get desirable results for the most commonly used resolution an minimize scaling artifacts. I have not tried this on the Mister before in any way, so I'm not entirely sure the aspect ratio correction would work, but I have done this with a PC emulation setup and a 15Khz CRT before and it looked very good.

I need to try that. It's an old 31Khz CRT so I'm not sure what resolutions it will support. Good tip on the particular filter to try though. My only worry is that 400 isn't going to to work well for 320x240 games.

[SuperBabyHix]

Yeah, it wouldn't help for anything other than 200/400 line resolutions. You could consider using a higher vertical resolution too, something like 1440x480 with vscale=1, which would let you have integer scaling 200/400/240/480 line resolutions, but the 200/400 ones wouldn't fill the screen all the way. You may be able to use the monitor's controls to fill the screen, but that might be a pain. Also, depending on your monitor, you may lose that scanline look.

[Caldor]

I have been experimenting, but I think I need do have something to compare to, something that shows how it is supposed to look with a real DOS resolution output for example. I got an old laptop that I setup Windows 98 on, so I guess that would be a good place to start.... but I also have some XP machines that I could probably get to use a DOS boot disk and it might even be possible to run Windows 95 or 98 on them. Since they have USB ports, CD drives and such that would make it easier to test stuff... but problem is likely lack of drivers. The Pentium 3 based Windows 98 laptop is probably the fastest solution, should already have what I need for a simple test.

But in my tests it seemed pretty good, except I began to suspect it had maybe mashed it to be too narrow, maybe because its set to 4:3 and expects a widescreen? But not entirely sure if it is doing that. But it does not fill out the screen even when I stretch it horizontally as much as possible... so it probably does do that.

I do also have a Commodore 1084S and a 15khz LCD, so that might help get the original output working without scalers and such.

[ash2fpga]

Ahhh, I was about to pull the trigger on a de10 nano dedicated for computer cores, hooked up to a PC monitor.

Don't let this stop you. The experience is amazing...

And ordered, lol.

I am curious what is causing the uneven scaling ("vertical line missing every so often"). I wonder if the scaling pipeline is using some math that is not always optimal (esp. where input actually matches output -- maybe it still uses division that does not always divide evenly)? Perhaps "superscaling" to a higher res would be a workaround? e.g., I think some of the pi solutions run at resolutions like 2048x240 for 240p outputs.

[thorr]

FYI - I put a suggestion in one of the open issues on the ao486 github page that could be a workaround. I suggest to have a feature that detects the resolution being set (640x400, 800x600, etc.) and tells the scaler to set it to that resolution automatically on the fly. To expand on that, it could be called something like autoscaler. There could be a table of resolutions for the autoscaler in the ini file, and it could really work with any core by setting auto_scaler=true for that core. If it detects resolution A, set Resolution A with these timings. If it detects resolution B that may be normally unachievable, set Resolution C with these timings in those cases. This would also help with various video modes and setting them to either 1280x720 or 1920x1080 whichever scales better, on flat/widescreen monitors, etc.

[SuperBabyHix]

I think that is definitely a good idea. With some of the computer cores (ao486, Amiga, Atari ST) supporting higher resolutions there is not always a good, one size fits all scaling solution. Whether it is, like you suggest, being able to specify multiple output resolutions, or possible being able to specify multiple vscale/scaler filter settings for various resolutions. That would also be beneficial for non-crt users.

For instance with the Amiga core I may want to run at vscale=1 with a scanline filter for all video modes less than or equal to 540 lines, but switch to vscale=0 and sharp interpolation filter for all modes greater than 540 lines.

[ash2fpga]

I suggest to have a feature that detects the resolution being set (640x400, 800x600, etc.) and tells the scaler to set it to that resolution automatically on the fly.

I like it! I imagine it would be nice as a main mister feature that could be added to other cores, like resolution-switching consoles (unless those already have features I do not know about).

[deepthaw]

I suggest to have a feature that detects the resolution being set (640x400, 800x600, etc.) and tells the scaler to set it to that resolution automatically on the fly.

I like it! I imagine it would be nice as a main mister feature that could be added to other cores, like resolution-switching consoles (unless those already have features I do not know about).

I like it in theory, but I've been seeing artifacts show up in the scaler even when theoretically doing 1:1 translations (see my photo at the very top...) Native VGA would be amazing.

[thorr]

I like it in theory, but I've been seeing artifacts show up in the scaler even when theoretically doing 1:1 translations (see my photo at the very top...) Native VGA would be amazing.

This may be fixable by adjusting your timings. It's not just the resolution, but the other settings that can affect how wide things show up on the screen, etc. Making your settings a bit wider with the same resolution may open up that missing pixel on the O in the scaler. I am not sure, but it is worth a shot.

Also, setting the resolution a bit wider by a couple of pixels may fix it too, like 722 instead of 720. The scaler might be adding its own border pixels causing the actual image to be squished into fewer pixels. Again this could be affected by the timings. Maybe setting the timings narrower at 720x400 rather than wider is the answer to eliminate those unwanted border pixels.

[thorr]

Also, is there a utility to affect the MiSTer video_mode settings from within DOS? If so, we could make batch files for our games to set the proper scaled resolution before the game starts.

[Televicious]

Pretty cool, dos text looks like illegible shit, and windows 3.11 is blown up in scale, but games look amazing at 15khz.

[akeley]

I wouldn't really say they look "amazing" if the scaling is wrong. You can see it even in this very picture.

This core is indeed amazing and I get it that people are excited about it, but we should not really settle for incomplete results. If there are possible solutions it's definitely worth researching. It is after all the display, something which you face at all times.

I'd appreciate if somebody could clarify if native VGA is simply not possible at all (and never will be) or is it question of dev interest. Sorgelig's explanation in that github issue thread is a bit too technical for me.

If native VGA really is a no-no then we can explore improving/tweaking the scaler perhaps.

[Televicious]

Well, the scaling is off because I'm running the 31k core on a 15k monitor with a custom expiramental video mode. It's not intended to actually function, but thanks to MiSTer it is magically working. I haven't tried native 31k on my 31k monitor because I use all sorts of cores on it that do need the scaling and it's easier to set the monitors native resolution as the end scale. It makes more sense that it switches the resolution on the fly internally outputting a constant native resolution. Which I might add 1280x960 seems to be perfect for a lot of the 640x480 stuff. Otherwise you have monitor signal searching, which you can miss a lot with LCD's doing that with games that do change resolution a lot, and need to reorient it constantly even on old vga crt's. I remember doing that with my 486's crt all the time, which is why they made those pot adjusters front and center in that era.

I'll give the scalerless option a go on the 31k just to see what you mean. Seems like it would work. It did the whole scrolling double image when i tried it on a 15k.

[Televicious]

Ok, so I tested it out. It's weird because I forgot the scalerless mister menu is like 240p which doesn't display without scaling on this monitor. Anyhow from what I can see is the main DOS mode works perfectly fine, the text actually looks much better unscaled. Now my 31k monitor is a dell 1908fp which won't display lower than 640x480 at a specific frequency. So anything that was intended to display at 200 or 240 does not sync. It would need an older vga or early svga crt. So I'm guessing it will work fine if you have the proper monitor. Though windows 3.11 did not show properly, but i had it set to a funky 480 setting that might not have the right frequency on the Dell. Though after reading that github thread it looks like it's designed to be scaled no matter what so it makes sense that the default dos resolution is the only thing that functions. Well, maybe someone will incorporate an unscaled vga mode down the line. I'd love a TTL output mode personally since I have a bunch of TTL monitors laying around, but ya know, it's a hobbyist product. Makes me want to learn how to solve it.

[akeley]

Could you, or somebody else post .ini settings for the unscaled VGA output? I've tried yesterday and was unable to do it. I'm using Direct Video though.

Are you sure it's really perect? Don't get me wrong, I really want to believe you but then we have this thread and git issue ticket. Also, not sure what exactly "proper monitor" means in this context. From my understanding VGA should display on any VGA capable monitor, and older 200/240 games were upscaled (though do not quote me on that )

[Televicious]

Oh I guess my post was confusing. You are correct. By perfect I mean the core boots and displays DOS commandline perfectly. However if I run anything that isn't that weird 720x400 DOS text resolution I get either a black screen or video garbage, and you are also right that VGA 200 or 240 should be scandoubled. I was just kind of speculating through the evidence to see what it was doing. The github post is correct and it is intentional that it works this way. Someone would have to program completely different video logic to handle native vga output, if even possible with the main mister output, and also maintain the current one to enable or disable or switch between to maintain that functionality with all the different displays that it does work on currently. Your best option is to set the scaler to the native resolution of your vga display and maybe someone will expand functionality eventually.

Btw, what kind of monitor are you using?

[akeley]

I have a few VGA monitors, mostly newer 17" ones. The one I've tried with MiSTer is SyncMaster 793df.

What mister.ini settings are you using for non-scaled VGA? I'd like to try it myself..

Overall, I have a bit of an OCD when it comes to displays, so will stick with my DOS PC for now. Hopefully one day there will be solution for this core too, stranger things have happened