VGA Mode Changing for 720x400 and 640x400

[FoxbatStargazer]

I just use 1600x400 with wide/full aspect, that's a 5x scale for games and 2x for DOS. I use HV integer so DOS text ends up a little tall/squished at 2x but its' still perfectly sharp. Another approach is to go 1440x400 for perfect DOS text while using sharp interpolation for a 4.5 game scale, which still looks pretty good.

[akeley]

Can you post your modeline/settings? I might give'em a try. For now I don't mind swapping rbfs to use solution from this thread, but it's far from ideal. I actually tend to use this core on my consumer TV more these days anyway.

I really hope eventually we will see a permanent 1:1 solution (with approximations my CRT OCD flares up).

[Nikoh]

right, @FoxbatStargazer modelines would be appreciated

[FoxbatStargazer]

video_mode = 1440,40,136,176,400,3,10,7,52500
video_mode = 1600,40,160,200,400,5,2,28,58500

I mostly make lines from here, and if they don't work, just play with the blanking lines a bit, it's all rather arbitrary and will vary based on your display.

Keep in mind this is 400p so you will need refresh rate variable and be running 70hz DOS stuff. 60 hz and you will probably lose sync on a VGA CRT.

[tsowell]

Hey,

Sorry to leave you all hanging, but I finally got around to trying to giving this a more proper treatment.

https://github.com/tsowell/Main_MiSTer/ ... modes-file
https://github.com/tsowell/ao486_MiSTer ... c-polarity

The custom modes are configurable now. You set the custom_video_modes_file option in MiSTer.ini to the path to the file your custom modes are in.

And you define modes in that file like:

Code: Select all

WIDTHxHEIGHT=MODE

MODE is the custom video mode (same format as used in MiSTer.ini) to use when the FPGA resolution matches WIDTH and HEIGHT. If you assign different modes to the same target resolution on multiple lines, MiSTer will store both and use whichever one most closely matches the vertical refresh rate of the FPGA's video mode. This might be handy on a display with one 50Hz resolution and one 60Hz resolution - you could use one for PAL and one for NTSC.

You can also specify sync polarity in custom modes now by appending two numbers to the end of the mode (0 for negative, 1 for positive). See my custom modes below for an example. This works anywhere custom mode strings are used, but the sync polarity will only change if the core supports it, and I've only added support to ao486. I think the patch should apply cleanly to any core though.


Here's how I have mine configured for my IBM 8512 monitor.

In MiSTer.ini I have:

Code: Select all

custom_video_modes_file=/media/fat/custom_modes

And /media/fat/custom_modes file has the following contents (semicolons start comments):

Code: Select all

720x400=720,15,108,51,400,11,2,32,28322,0,1 ; 720x400@70Hz -hsync +vsync
320x200=640,16,96,48,400,12,2,35,25175,0,1  ; 640x400@70Hz -hsync +vsync
640x400=640,16,96,48,400,12,2,35,25175,0,1  ; 640x400@70Hz -hsync +vsync

This matches the configuration I hard-coded in the proof-of-concept last year. Note the optional "0,1" parameters at the end of the modes to specify negative hsync and positive vsync polarity. If they are omitted, both polarities default to negative.


Anyway, MiSTer and ao486.rbf binaries are attached. Like last time, you only need the rbf if you want to change sync polarity, but you'll need to use this version of the rbf with this version of MiSTer because I've changed the way sync polarity is set over SPI.

Let me know if this whole setup is sensible or if I'm missing anything. I plan to open a PR for it, but I thought it would be good to run it by you folks first.

[flynnsbit]

I want to thank you so much for doing this. I think this PR is a must at this point. I was still using your old version most of them time and glad you are still around! Please do submit the PR when you feel comfortable and I will run back through this setup with the version you attached.

[akeley]

Yes, your reappearance with a new build of this niche-but-crucial tool is one of the pleasant surprises I love MiSTer for Here's hoping it'll get merged sooner rather than later...

[FoxbatStargazer]

Best part of this approach, is that you can build a custom resolution that retains the correct aspect ratio for Jazz Jackrabbit's 199p/60hz mode.

[atrac17]

Hey,

Sorry to leave you all hanging, but I finally got around to trying to giving this a more proper treatment.

https://github.com/tsowell/Main_MiSTer/ ... modes-file
https://github.com/tsowell/ao486_MiSTer ... c-polarity

The custom modes are configurable now. You set the custom_video_modes_file option in MiSTer.ini to the path to the file your custom modes are in.

And you define modes in that file like:

Code: Select all

WIDTHxHEIGHT=MODE

MODE is the custom video mode (same format as used in MiSTer.ini) to use when the FPGA resolution matches WIDTH and HEIGHT. If you assign different modes to the same target resolution on multiple lines, MiSTer will store both and use whichever one most closely matches the vertical refresh rate of the FPGA's video mode. This might be handy on a display with one 50Hz resolution and one 60Hz resolution - you could use one for PAL and one for NTSC.

You can also specify sync polarity in custom modes now by appending two numbers to the end of the mode (0 for negative, 1 for positive). See my custom modes below for an example. This works anywhere custom mode strings are used, but the sync polarity will only change if the core supports it, and I've only added support to ao486. I think the patch should apply cleanly to any core though.


Here's how I have mine configured for my IBM 8512 monitor.

In MiSTer.ini I have:

Code: Select all

custom_video_modes_file=/media/fat/custom_modes

And /media/fat/custom_modes file has the following contents (semicolons start comments):

Code: Select all

720x400=720,15,108,51,400,11,2,32,28322,0,1 ; 720x400@70Hz -hsync +vsync
320x200=640,16,96,48,400,12,2,35,25175,0,1  ; 640x400@70Hz -hsync +vsync
640x400=640,16,96,48,400,12,2,35,25175,0,1  ; 640x400@70Hz -hsync +vsync

This matches the configuration I hard-coded in the proof-of-concept last year. Note the optional "0,1" parameters at the end of the modes to specify negative hsync and positive vsync polarity. If they are omitted, both polarities default to negative.


Anyway, MiSTer and ao486.rbf binaries are attached. Like last time, you only need the rbf if you want to change sync polarity, but you'll need to use this version of the rbf with this version of MiSTer because I've changed the way sync polarity is set over SPI.

Let me know if this whole setup is sensible or if I'm missing anything. I plan to open a PR for it, but I thought it would be good to run it by you folks first.

Outstanding work.

[thorr]

This is fantastic and greatly appreciated! I wish it was standard across all cores! Any chance to add interlaced support so we can use 480i on CRT TV's?

[FoxbatStargazer]

I don't think this is "direct" analog output, it's just changing the resolution of the scaler used across the Mister framework. The scaler currently has no interlacing support, so...

[thorr]

Correct but I was hoping the scaler could be improved by adding interlaced support since positive and negative sync was added. It could convert 480p to 480i. It would be missing half the lines drawn in 480p as it skips every odd line then every even line drawing down the screen but for static or slow moving images this could be acceptable. Then using integer scaling, 400p/i would be possible so it wouldn't have overscan issues.

[tsowell]

I wondered if it might be useful to change more than just the video mode based on different core video modes, so I'm looking at moving the configuration into sub-sections of MiSTer.ini, so you can do stuff like:

Code: Select all

[video=320x200]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.0]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

I think it will also make it a little more intuitive than having a whole new special file format just for this.

I'm thinking if there's an exact match between the core's resolution and vertical refresh rate, it will use those settings. If no sub-section specifies a matching rate, it will fall back to one that matches the resolution and has no rate specified. Otherwise it will finally fall back to the [MiSTer] and core-specific settings.

[flynnsbit]

Yeah, that's a really good idea.

[flynnsbit]

I wondered if it might be useful to change more than just the video mode based on different core video modes, so I'm looking at moving the configuration into sub-sections of MiSTer.ini, so you can do stuff like:

Code: Select all

[video=320x200]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.0]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

I think it will also make it a little more intuitive than having a whole new special file format just for this.

I'm thinking if there's an exact match between the core's resolution and vertical refresh rate, it will use those settings. If no sub-section specifies a matching rate, it will fall back to one that matches the resolution and has no rate specified. Otherwise it will finally fall back to the [MiSTer] and core-specific settings.

Do you use Discord? There's a nice community of like minded people that love talking about the computer cores and specifically AO486. https://discord.com/channels/6479093974 ... 8162279424

[tsowell]

Here's a version that supports video-mode-specific sub-sections in MiSTer.ini that can be used to override any configuration option. I'm much happier with this scheme.

https://github.com/tsowell/Main_MiSTer/ ... -overrides

Section names must follow the format "video=WIDTHxHEIGHT[@VREFRESH]". MiSTer will first look for an exactly-matching WIDTHxHEIGHT@VREFRESH section, and if one isn't found, it will fall back to a matching WIDTHxHEIGHT section if present.

Code: Select all

[video=320x200]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.1]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

There are a couple of caveats. One is that these sections should be the last sections in MiSTer.ini (so that they can "see" the preceding MiSTer/core options that they are not overriding).

The other is that in order to match by vertical refresh rate, the rate in the section name must match exactly the vertical refresh rate in video_info or the debug log. If MiSTer reports "640x480 31.47KHz 60.0Hz", the section title needs to be "[video=640x480@60.0]" in order to match. In other words, there's no fuzzy matching of refresh rate like in my previous attempt. (Though now you can at least use the existing video_mode_pal and video_mode_ntsc options in a video override section).

[akeley]

Fingers crossed: https://github.com/MiSTer-devel/Main_MiSTer/pull/567

[flynnsbit]

Here's a version that supports video-mode-specific sub-sections in MiSTer.ini that can be used to override any configuration option. I'm much happier with this scheme.

https://github.com/tsowell/Main_MiSTer/ ... -overrides

Section names must follow the format "video=WIDTHxHEIGHT[@VREFRESH]". MiSTer will first look for an exactly-matching WIDTHxHEIGHT@VREFRESH section, and if one isn't found, it will fall back to a matching WIDTHxHEIGHT section if present.

Code: Select all

[video=320x200]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.1]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

There are a couple of caveats. One is that these sections should be the last sections in MiSTer.ini (so that they can "see" the preceding MiSTer/core options that they are not overriding).

The other is that in order to match by vertical refresh rate, the rate in the section name must match exactly the vertical refresh rate in video_info or the debug log. If MiSTer reports "640x480 31.47KHz 60.0Hz", the section title needs to be "[video=640x480@60.0]" in order to match. In other words, there's no fuzzy matching of refresh rate like in my previous attempt. (Though now you can at least use the existing video_mode_pal and video_mode_ntsc options in a video override section).

Congrats on the merge! This is my favorite feature, hands down.

[HMPoweredMan]

Wooh! Finally congrats!
Is there a list of common resolutions used in the 486 core with the appropriate video_mode equivalents?

[Shogun]

Yay thanks for this! Agreed we could use a list of common resolutions. I've just been using the two in the example so far which has worked fine and then default to 640x480 modeline built into Ao486 for everything else.

[cursedverses]

@HMPoweredman http://tinyvga.com/vga-timing is a useful resource here - you can use its tables (minus whole line/whole frame) and the pixel clock number multiplied by 1000 to create your mode lines. You may need to lower clock speeds for certain lines though (e.g. 720x400@85Hz, you want to lower to bring the clock down to 70Hz)

Of course, if anyone has a better resource...

also, @tsowell thanks so much for this! I've literally just acquired a CRT and was wondering if there was this exact functionality available in MiSTer!


I do have a question though, does the screen mode change regardless or does the code check to see if the mapping is the same as current?

[cursedverses]

Also, https://www.epanorama.net/faq/vga2rgb/calc.html for altering screen modes, and https://courses.cs.washington.edu/cours ... mation.pdf seems to be a decent resource.

[Shogun]

I wrote a brief guide on modelines a while back but haven't messed with any of that in a while so I'll have to do some reading again - viewtopic.php?t=3249

Oh yea also also a ton of modelines here: https://github.com/glopgar/MISTer_video_modes

[geiger9]

so I have tried this new option but my VGA CRT keeps reporting it is being fed 15khz. I thought setting the vga_scaler=1 would solve that problem? Is there something else besides the code above that I should be entering in my ini file?

[thorr]

I finally got around to trying this. It is an amazing feature, and now I am very happy to share my new modelines that I have generated so far. Dos text and 320x200 games are pixel perfect and spot on synchronized to the correct refresh rate and look absolutely fantastic.

To be clear, this is actual 320x200 with scan lines, like how it looked on hardware back then. Not upscaled to 640x480. It looks way better in my opinion. It doubles the frequency to 140.2 Hz so the monitor can display it. Also the DOS text mode is actually 70.1Hz. The suggested modeline above is not.

[ao486]
; Set it to "Variable" in the video settings in the menu of the core
video_mode=1600,64,192,304,1200,1,3,46,162000 ; 1600x1200x60Hz I need to update this one to 70.1 Hz too just for good measure
direct_video=0 ; use the scaler
vsync_adjust=2 ; minimal lag
vscale_mode=1 ; integer scaling
video_info=3 ; show resolution information for X seconds
hdmi_limited=2 ; 1 - use limited (16..235) color range over HDMI
; 2 - use limited (16..255) color range over HDMI, for VGA converters.

[video=320x200@70.1]
video_mode=320,24,49,38,200,2,2,20,13535,0,1 ; 320x200@140.2Hz@31.4kHz DOS Games

[video=720x400@70.1]
video_mode=720,15,108,46,400,13,2,34,27983,0,1 ; 720x400@70.1Hz@31.48kHz DOS Text

A special shout out to akeley: Give these a try on your VGA monitor. You may like this better than your CRT TV!

Here are pictures from my VGA monitor using my phone. It looks way better in person. (open in a new tab to see native resolution):

Edit: Ignore my Monkey Island 2 screenshot, because the 320x200@140.2Hz modeline is for EGA and CGA games (at most 16 colors).

[Schyz]

Hi,

I use AO486 with a CRT monitor, if this has been merged, is there any documentation about this feature?

Do I only have to add the following under the [ao486] section

Code: Select all

[video=320x200@70.1]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.1]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

And set Wider HV-Integer scaling?

[thorr]

Hi,

I use AO486 with a CRT monitor, if this has been merged, is there any documentation about this feature?

Do I only have to add the following under the [ao486] section

Code: Select all

[video=320x200@70.1]
video_mode=640,16,96,48,400,12,2,35,25175,0,1
vscale_mode=2

[video=720x400@70.1]
video_mode=720,15,108,51,400,11,2,32,28322,0,1

And set Wider HV-Integer scaling?

See my post above yours. I recommend my modelines instead. I also provided all of my other settings. You need to set it to "variable" in the menu.

[FoxbatStargazer]

What I really want to confirm is whether supplying a list of resolutions is framework-wide now, and can be used in other cores? Or is it specific to AO486?

[thorr]

Update: So, for 320x200 games, if they are CGA/EGA era games (earlier Sierra games), use the 320x200@140.2Hz modeline I provided. If they are VGA era games, there should not be scan lines. I created a new modeline that is perfect for many VGA era games. These resolutions are 320x200, 320x400 and 640x400. They all can be integer scaled to 640x400@70.1Hz. I tested with Second Reality and it makes it all the way through and there are no audio glitches except at the beginning. Here is the latest:

[video=320x200@70.1]
;video_mode=320,24,49,38,200,2,2,20,13535,0,1 ; 320x200@140.2Hz@31.4kHz DOS CGA/EGA/Adventure games with scanlines
video_mode=640,7,108,30,400,13,2,34,24708,0,1 ; 640x400@70.1Hz@31.48kHz VGA era games including 320x200, 320x400, 640x400 @70.1Hz

[video=320x400@70.1]
;video_mode=320,15,108,46,400,13,2,34,15392,0,1 ; 320x400@70.1Hz@31.48kHz This is not finished (not wide enough), but also not needed
video_mode=640,7,108,30,400,13,2,34,24708,0,1 ; 640x400@70.1Hz@31.48kHz VGA Games including 320x200, 320x400, 640x400 @70.1Hz

[video=640x400@70.1]
video_mode=640,7,108,30,400,13,2,34,24708,0,1 ; 640x400@70.1Hz@31.48kHz VGA Games including 320x200, 320x400, 640x400 @70.1Hz

[video=720x400@70.1]
video_mode=720,15,108,46,400,13,2,34,27983,0,1 ; 720x400@70.1Hz@31.48kHz DOS Text

[thorr]

What I really want to confirm is whether supplying a list of resolutions is framework-wide now, and can be used in other cores? Or is it specific to AO486?

I don't know yet, but I am guessing it is global. It can be easily tested by running another core, showing what resolution it uses, and then define a modeline that it can upscale to, like 1600x1200 in the ini file for it and see if it uses your modeline.