Weird emulation problem. SNES & Genesis

[stinky180]

So I finally got FreeMC Boot installed and started to mess around with my PS2. I love all the homebrew stuff that is available. I decided to get a network adapter so I can use a hard drive. I finally got the HDD set up and figured I would test out an emulator. So I went ahead and downloaded PGEN and SNES-Station from sksapps.

Games do work fine except for one problem.

Whenever there is movement on the screen (character moving around) the screen literally flickers. In A Link To The Past, after link gets out of bed and you move around; the screen just flickers. You can still see what is on the screen but the screen flickers. When there is no movement, the picture is perfectly fine.

At first I thought it may be SNES-Station was at fault, so I tried the PGEN Genesis emulator. The same flickering light thing is here too!

Has anybody experienced this type of problem?
The emulators work great except for this light flicker while moving around...
Anyone have any suggestions for me?

Details:
PS2 Fat 31000R
Modem & Ethernet Network Adapter
Seagate 10gb HD
FreeMC Boot noobie package

The settings in both emulators are set to USA as well. Please oh please help me.. thanks!

[lee4]

We need know video cable are you using and TV type you got.

[stinky180]

Using OEM Sony Component Cables; 3x video 2x audio
37" LCD TV; 1080i

[lee4]

Manufacturer & Model?

I do not any video problem on my Tashiba LCD TV using Component Cable.

You try change SNES-Station settings (/\ button)

you sure that you change
Display Mode : AUTO
to NTSC?

lastest of the two emulators
http://psx-scene.com/forums/showthread.php?p=447296

[stinky180]

Manufacturer & Model?

I do not any video problem on my Tashiba LCD TV using Component Cable.

You try change SNES-Station settings (/\ button)

you sure that you change
Display Mode : AUTO
to NTSC?

lastest of the two emulators
http://psx-scene.com/forums/showthread.php?p=447296

Dynex; unsure of the model but there is only one 37" LCD they have

Yes, it is set to NTSC and I'm still getting the weird flickering problem. Maybe I'll take a video... I'll also try out the latest SNES-Station (sksapps may be outdated??)

[lee4]

you got lo-end TV.

you try other emulators infoGB, FCEUX, etc. even PS1 games to see this flicker still exist.

[stinky180]

All emulators flicker

PS1 and PS2 games work perfectly fine

[dlanor]

All emulators flicker

PS1 and PS2 games work perfectly fine

It sounds to me as if this TV set has a problem with non-interlaced SDTV modes, which are the natural modes to use in emulating an old console type with low resolution video.

I've heard of this kind of problem before with some HDTV sets.

In dealing with normal PAL or NTSC video they assume it is interlaced and insist on using two alternating buffers filled with odd and even half-frame data respectively, but base the choice not on frame counting, but on the frame timing. So depending on where in a scanline the VSync occurs it is judged to be either odd or even. For a non-interlaced PAL or NTSC mode this leads to all half-frames being considered to be the same, either odd or even, filling only one of the buffers. And then the other buffer contains either garbage or some old screen data but is still displayed alternately with the working buffer. This results in 25 or 30 Hz flicker in alternation between correct screen data for one half-frame set and garbage/old data for the other half-frame set.

This is simply a stupid error on concept level in the design of such a TV set.

You could try using GSM to enforce either NTSC or PAL mode with normal interlace.
This works rather well for me, though I don't need it for your reasons.

This should work, though you may need to 'tweak' the DH and DY settings a bit to get a proper combination of vertical scaling and positioning, if using NTSC on a Euro console (or any case where SNESstation may 'want' to normalize the requested resolution for PAL standards). One good way to do that is to start from base NTSC mode and then raise DH by 64, from 447 to 511, and then lower DY by half that amount, from 46 to 14 or so to compensate for correct centering. Some additional DY tweaking may be needed for perfect centering after tests. And then you can save the resulting video mode in the user mode array of GSM and save that to GSM.CNF for simple future reuse.

This should allow both the SNESstation GUI and all emulated games to display correctly.
(I just tried it with "Chrono Trigger" here and it looks fine to me.)

And since the enforced mode is normal interlaced NTSC, your TV set should not flicker at all.

Best regards: dlanor

[stinky180]

You could try using GSM to enforce either NTSC or PAL mode with normal interlace.
This works rather well for me, though I don't need it for your reasons.

This should work, though you may need to 'tweak' the DH and DY settings a bit to get a proper combination of vertical scaling and positioning, if using NTSC on a Euro console (or any case where SNESstation may 'want' to normalize the requested resolution for PAL standards). One good way to do that is to start from base NTSC mode and then raise DH by 64, from 447 to 511, and then lower DY by half that amount, from 46 to 14 or so to compensate for correct centering. Some additional DY tweaking may be needed for perfect centering after tests. And then you can save the resulting video mode in the user mode array of GSM and save that to GSM.CNF for simple future reuse.

Best regards: dlanor

Thanks for the suggestion dlanor! I'm in the US so its NTSC. I'm trying to play around with GSM but I'm quite a noobie at all of this. If i understand correctly;

Under 'PREDEF VMODES'
CURRENT: *should be set to NTSC by using the O button
(I'm not exactly sure which one to choose..)

Should the Interlace=1 or 0?

I've been trying different VMODES but the screen always tends to be way off center (can't see anything sometimes).

If you have any tips, that would be great! Thanks for providing such great software to the homebrew community!

-180

[dlanor]

Thanks for the suggestion dlanor! I'm in the US so its NTSC. I'm trying to play around with GSM but I'm quite a noobie at all of this. If i understand correctly;

Under 'PREDEF VMODES'
CURRENT: *should be set to NTSC by using the O button
(I'm not exactly sure which one to choose..)

The 'O' button is used to step through the list of SDTV video modes, with the first entry in that list being normal NTSC, displayed as "NTSC-I Full Buffer". And that mode is the only one you really need to use, for the purpose we've discussed.

If you've messed around with other buttons you can always get back to that setting by first pushing a button intended for video mode lists of other video mode groups (Triangle==VGA, Square==HDTV, X==PS1 support (via HDTV)). Whenever you've used a mode group button, all of the others are reset to their first entry, so pushing the 'Triangle' button for a VGA mode means that the 'O' button is reset to give the base NTSC mode when next you press it, no matter what it was earlier.

Selecting a video mode this way does not activate it though, which only happens when you press the Dpad_Down button (alone).

So if you mess up and lose visibility, a simple way to get it back is to just press three buttons, one at a time, like 'Triangle', 'O', 'Dpad_Down'. That will select and reactivate normal NTSC mode, with all default settings, so you can start over.

Should the Interlace=1 or 0?

Since your TV has a problem without interlace, that should be on == 1, which it always will be for the setting I told you how to reach above.

I've been trying different VMODES but the screen always tends to be way off center (can't see anything sometimes).

Well, for any TV/Monitor there are always some modes it can't use, and some PS2 bios versions don't support all modes anyway (many crash if trying HDTV 576p).

But assuming you are using normal SDTV modes that your TV can sync to, you should always be able to center the display, and if that fails then you need to learn how to control it.

The size of the screen, as used for rescaling, is set by the right joystick, affecting DW and DH values in the presets (Width-1 and Height-1), while the positioning of that used screen is set by the left joystick, affecting DX and DY values in the presets. The size controls are also modified in magnitude by L1 and R1 buttons. L1=>Steps of 1 unit, R1=>Steps of 16 units, neither=>Steps of 4 units. The modifiers need to be pressed while pushing the joysticks. Thus holding down R1 while pushing the right joystick to the right three times will increase the DW value by 3*16 == 48 units (VCK units, normally 4 per pixel in standard 640x448).

Tweaking size and position like this is in a way like the basic mode selection, in that it only affects the numbers held in the preset values, until you activate the current preset data by again pressing Dpad_Down (alone).

Btw: Note that Dpad_Down is sometimes used as a command modifier, for commands started by first holding another button, so to use it for the activation command all other buttons should be released.

So normally 'tweaking' is done by first handling a joystick to modify one or more of the values, and then pressing Dpad_Down to inspect the result on effective centering and fillout (though game fillout may differ, its centering never should). Keep this up until you are happy with the results, and then either save the mode in the user array and GSM.CNF for the future, or just exit to use the mode directly.

The fillout of the screen will not be done identically for a game, because they always use standard resolutions which can't always be scaled well for an enforced video mode. But the centering should always be the same as displayed in GSM, unless a game is badly incompatible.

Also, the scaling should not be much of a problem for you, if you stick to normal NTSC. For many NTSC games this is the native mode, while lowres non-interlaced games (the ones you had trouble with) have half of that, so their pixels will simply be doubled for perfect fillout. But there will be a problem with Euro games using PAL, since they have larger video height than their NTSC counterparts. So with standard NTSC settings GSM will be unable to double the pixels, as that would require a raw DH value of at least 511, to cope with vertical doubling of non-interlaced PAL using 256 pixels' height.

And that is what I was talking about in an earlier post. If a game or an emulator 'wants' to use a PAL mode (maybe because of a Euro ROM to be emulated), then you need to have DH raised to a value normal for PAL, which is 511 (for a height of 512) and with that done you will need to compensate for this change by decreasing DY, so as to keep the picture centered.

Some of this enlarged picture will be outside of the visible screen, even in the GSM GUI, but this does not matter. Games using normal NTSC mode should display scaled and centered as usual (subject to DX and DY tweaks), while PAL games should display as well as they can. Some of their lines will be above and/or below the visible range, but that is unavoidable when trying to display 512 lines with only 448 lines available (and without fractional scaling available).

This is still a great improvement over the case without enlargement, where a non-interlaced PAL game would be displayed at effectively half height (no doubling allowed by the low DH value), with appx 42% of the screen filled with black borders (21% each at top and bottom).

Best regards: dlanor