Limit Scandoubler to 15kHz Modes?

[mapf]

Hi all,

my MiSTer is connected to a Dell VGA CRT monitor. I am using the analog output of the I/O board. The settings have forced_scandoubler=1, so all 15KHz signal get doubled to 31KHz signals that work with a modern VGA monitor.

On the minimig, this is working fine for all PAL or NTSC modes.

But with the higher resolution RTG modes, the scandoubler apparently also doubles the frequency. The screenshots show that for the 1024*768 RTG mode, a 62KHz signal is generated. The monitor menu shows it as 66KHz.

Is there a way to limit the scandoubler to 15KHz modes, so that native 31KHz signals are left as they are?

[mapf]

I connected an additional HDMI monitor to my MiSTer and removed the forced_scandoubler setting. On HDMI, everything works as expected.

But VGA is weird: MiSTer on-screen information shows that the signal is supposed to be 31KHz, but my CRT OSD shows exactly the same 66KHz signal as with the forced_scandoubler active (see picure above). Too me, this implies that the wrong 66KHz analog signal is generated by the RTG mode, and not the scandoubler.

Is anyone else using minimig with a CRT and has the high-res modes working without falling back to the vga_scaler?

[DoubleA]

I can confirm that, Minimig RTG modes, VGA and scandoubler are currently not a good combination.
Not only with CRTs, LCDs with VGA input have the same issues.

[Lisko]

As the RTG uses the scaler to draw the images, try removing scandoubler option, set a compatible screenmode for your monitor with the same resolution rtg will use and also set vga_scaler = 1
Unfortunately I don't have a crt to test with but could work.

[mapf]

Yes, it works with a fixed resolution and vga_scaler - but this defies the purpose of using a CRT monitor that can easily switch between hi-res RTG and the traditional NTSC/PAL modes.

[FoxbatStargazer]

Isn't 1024x768 supposed to be around 48khz? If you want to blame scandoubler for 66khz it wouldn't be due to doubling the vertical resolution, which its not because it looks like it only gets to 990 px vertical? If it were the scandoubler's fault it would be like it was adding only 222 resolution or roughly 15khz worth, which would have to be some kind of bug.

Can you verify unwanted artifacts from only some lines being doubled? Maybe this extra "resolution" is placed in the overscan area?

[mapf]

I agree it is most likely not the scandoubler, but something else. See my second post in this thread - if the scandoubler is disabled, the weird 66KHz signal is still the same. So the thread title is now a little misleading.

Then again, I would love to have a regular 1024x768 signal when using RTG with a CRT.

[DoubleA]

Isn't 1024x768 supposed to be around 48khz? If you want to blame scandoubler for 66khz it wouldn't be due to doubling the vertical resolution, which its not because it looks like it only gets to 990 px vertical? If it were the scandoubler's fault it would be like it was adding only 222 resolution or roughly 15khz worth, which would have to be some kind of bug.

Can you verify unwanted artifacts from only some lines being doubled? Maybe this extra "resolution" is placed in the overscan area?

What i can confirm is that an Amiga Mister-RTG screenmode of 640 x 480 resolution is doubled to 1280 x 960 with scandoubler ON (and vga_scaling = 2).
Mister RTG-resolutions with more than 540 lines are non-integer scaled AND use weird frequencies on a Full-HD display and the Amiga OS guru meditates after a few seconds when switching to such resolutions.

Mister RTG resolutions should just ignore ALL scandoubler and scaling options to work as expected.

[FoxbatStargazer]

Not sure if vga_scaler=2 does anything different, I thought it was 1 or 0.

Also the horizontal resolution doubling is strange, because normally the scandoubler only changes the vertical resolution.

Check mapf's claim if you can, what happens to these RTG resolutions with scandoubler off? (Also make sure scandoublerfx are disabled?) If you can't boot into RTG and don't have an HDMI display around to navigate, you might be able to start the core with a scandoublerfx on, then disable it after you switch to RTG.

I guess what is further weird is that "guru meditation" = internal Amiga error, right? Is the Mister display even relevant for that? Does it crash the same under vga_scaler?

[DoubleA]

I guess what is further weird is that "guru meditation" = internal Amiga error, right? Is the Mister display even relevant for that? Does it crash the same under vga_scaler?

To guess a little bit more, this could be a hint, that the Mister monitor device is not perfectly Amiga OS friendly.

That's my Minimig config for a Full-HD monitor and VGA input (works perfectly for native PAL Amiga screen modes):

[Minimig]
vga_scaler = 1
forced_scandoubler = 1
vscale_mode = 2
video_mode = 9
key_menu_as_rgui = 1
vsync_adjust = 0