Not understanding video: 640x400 from HDMI port?

[callanabrown]

Ok so I am trying to use my Mister with a max 1600x1200 VGA CRT. My understanding that a regular old DOS mode would be 320x200 but then is typically scan-doubled by the VGA card to 640x400. So I assume when I turn on my real Pentium II machine, 640x400 is what I see.

So, using the HDMI port and an HDMI to VGA converter, is there any way to get 640x400? I do not have an I/O board since everything else I do is through direct video to another 15 kHz monitor.

I have tried all the combinations of forced_scandoubler, vga_scaler and direct_video, and I've also tried them with a custom video_mode line. I get solid signals with forced_scandoubler on, but the scaling is all messed up.

Any ideas? Do I have my facts straight about the DOS resolutions? To be honest before looking into this I assumed DOS was 640x480.

[mapf]

Hi,

I think you got all the important facts right. In my setup with both a VGA CRT and a TFT (for "tate" arcade games), I use the following mode with the CRT connected to analog I/O. It should also work with direct_video.

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[ao486]
;use with external filter "interpolation sharp" for readable text
vga_scaler=1
video_mode=640,24,96,40,400,9,2,39,25175; 640x400 (Good for 320x200 games)
custom_aspect_ratio_1=16:10 ;for proper scaling to the 640x400 resolution (but using "fullscreen" also works)

This gives a nice picture for 320x200 DOS games. Be aware that some of the later DOS games use 640x480 SVGA resolutions and will not look right with this mode. Depending on your setup you should experiment with

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vsync_adjust 

as well, as DOS uses higher refresh rates in text mode and this can lead to a lot of refresh rate changes.

[callanabrown]

Thanks for the suggestions but it doesn't seem to help my case. It seems like no matter what, the HDMI output (that I'm converting to VGA) is locked to a 31 kHz mode that does this strange scaling. Hopefully direct video can be implemented in the future in a way that mimics an original system with resolution switching.

[mapf]

That is perfectly normal. The mode line I gave is for a 31KHz VGA signal.

DOS VGA text mode is 720x400, and that does look squished like in your picture when scaled to a 640x400 resolution (you can improve the readability with the interpolation filter in the OSD). When running a game, resolution switches to 320x200 and all is fine.

[FoxbatStargazer]

Try 1440x400, most CRTs can handle it and that is a clean integer scale for 720 wide command prompt and a fairly clean 4.5x scale for 320 wide games. (try billinear sharp or horizontal-only filters) Or 1280x400 or 1600x400 if you want razor sharp games with less garbled command prompt. Set aspect ratio to "wide" in the core's HUD menu, the CRT will take care of squishing these odd resolutions to a 4:3 aspect ratio.

[callanabrown]

I eventually figured out my problem was the option in the ao486 menu - I had to switch aspect ratio from normal to full screen I believe. The modeline previously mentioned for 640x400 works great.