15Khz 240p wavy top

[contemplator]

Hi,
I have a TV set capable of both NTSC and PAL via vga-to-scart. All other resolutions/cores are working fine in GA2021 except when it comes to Retroarch NTSC 240p output.

I chose generic_15 and arcade_15 monitor presets and the issue persists. When I select INI CRTswitchres mode with ntsc monitor preset, 240p cores do not display any output.

I did not have this wavy top image problem using switchres with standalone Mednafen, and ntsc preset in GA2019. Wavy lines also do not appear in GroovyMAME with ntsc monitor preset in GA2021. So the problem is definitely with Retroarch.

I saw a post where someone had a similar issue and managed to resolve it using arcadeosd by adjusting the values 15.6 - 15.7Khz.

Also, in RA log i can see that the generic_15 and arcade_15 preset are both using 15.6xx Khz [PAL] instead of 15.7xxKhz [NTSC] frequency.

Is this perhaps a bug or is it a problem with different preset values for ntsc 240p output in Retroarch?

[buttersoft]

OK, so, IIRC correctly, this is a sync timing issue. Which is almost certainly due to how programs are outputting (composite) sync and/or how you're combining sync for yourself. It is possible that your set has a pot or service menu option to help with this, but not likely.

Why only certain program are affected, IDK, but i've seen programs do all sort of weird stuff, including writing/forcing their own modelines. Technically GM does that too, I guess.

I'm almost certain there was a thread about this issue on Shmups a while back, and I'm hoping Zebidee sees this thread on here and can explain more

[Calamity]

Hi contemplator,

Make sure you get RA using the ntsc preset. It's certainly possible, please post a full log to help understand what's going on. In any case, it must be a matter of RA configuration.

[makya]

Hello, I saw this before on my tv. It was due to a too short vertical sync time iirc.

[contemplator]

So after many hours of testing with different cables, and even a different TV set - and after updating RA to 1.9.10, I finally have some conclusions:

1. I replaced the graphic card HD 6450 with HD 5450, and now I have output on RA with 240p regardless of preset (ntsc is working as expected).

2. The wavy lines persist on generic_15 preset only when using ntsc rom. I noticed that the only difference comes with these two lines from RA logs

generic_15 - wavy
[INFO] Switchres: Modeline "256x224_60 15.625691KHz 60.098812Hz" 5.172103 256 266 290 331 224 233 236 260   -hsync -vsync

ntsc - works
[INFO] Switchres: Modeline "256x224_59 15.704280KHz 59.940000Hz" 4.852622 256 263 286 309 224 236 239 262   -hsync -vsync

So I think the problem is that generic_15 preset is using 15.625691KHz, instead of 15.704280KHz for ntsc content, but I`m no expert on the subject.

Hope it helps for further troubleshooting if anyone cares having ntsc content running correctly under generic_15 or arcade_15 preset.

Thanks!

[makya]

Well, maybe your TVs don't like vertical frequencies above 60Hz and/or total lines below 262 and/or large horizontal back porches. Can't see by the modelines what else could be an issue. What TV sets are you running on?

[contemplator]

Sony Trinitron standard consumer set (not the 100khz one). I also tried on B&O but the problem is the same on both when it comes to generic_15 and arcade_15 presets.

Like Calamity said it is only manifested in Retroarch, GM is working ok.

Maybe this is a question for Retroarch forums, but I figured since its GA2021 maybe someone else experienced something similar..

Anyway, I greatly appreciate your inputs it took me in the right troubleshooting direction.

[Calamity]

Your TV needs a longer vertical back porch. You can solve that with a custom monitor preset.

[contemplator]

I wanted to try a custom preset, but I was not sure what values I need to change. It`s ok to switch presets when needed, but a uniform solution is definitely preferable.

I will try when I catch some free time.

[contemplator]

Increasing the generic_15 value for the vertical back porch to 1100 did resolve the issue for the NES cores, but not for Genesis and SNES. This applies to both TV sets.

For the latter we tried incrementally raising the value until display went into some sort of interlaced mode, but with no success..

Are there any other values that could be changed which are specific to these cores?

[Calamity]

Try raising the hfreq_min value to 15.72 kHz.

[contemplator]

Value for hfreq_min was already in range copied from generic_15 for the custom preset
   
      crt_range0  15625-15750, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.100, 0, 0, 192, 288, 448, 576

I tried "hardcoding" various single 15.7x values, without success. It seems that for anything above 15.625Khz it goes into interlaced mode.

[Calamity]

 crt_range0  15720-15750, 49.50-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.024, 0, 0, 192, 288, 448, 576

[contemplator]

That solved the issue!  Thank you Calamity 

[contemplator]

I need to add some observations for any noobs out there like myself. Changes to the values for a custom preset significantly improved overall TV geometry and performance on all RA cores (and there I was thinking that my TV set is not quite right).

- Image is no longer moved to the left, which I see is a common issue with rgb/scart type of input on consumer sets
- I no longer see a slight stutter in image scrolling (which I think was causing the Attract mode to freeze) so everything seems to be in sync

Once again, thanks for helping I`m sure someone else will find this info useful as well.