Scanline limits for NTSC and PAL TVs

[+stephena]

I'm considering adding better limits for the TV/TIA emulation, since quite a few people have been messaging me about it. Basically, Stella treats a ROM as NTSC or PAL, with an upper limit for scanline count for each mode. Problem is, all counts are treated equally. For example, if a game runs at 262 lines, then it's a proper NTSC signal at 60Hz. However, if it runs at 280 lines, it's still an NTSC signal, and is rock-solid in emulation. On some TV's, though, this will cause a roll.

 

So my question is, what are the upper limits for screen roll? I know it won't be a single number (some TV's will have different behaviour), but I need a number to default to.

[Thomas Jentzsch]

I doubt you will get a good answer here.

 

I know that some NTSC displays roll(ed) on a version of Artillery Duel, which displayed just 239 scanlines. And then there are PAL TVs which can handle those 239 scanlines.

Sometimes it depends on the input. E.g. my Sony PAL rolls NTSC games via antenna. But not via composite or SCART (from a VCR with antenna input). Desert Falcon display 281 scanlines and IIRC a very few people reported rolling here on AtariAge.

 

The other extreme are late PAL games like Pick'N'Pile (or was it Acid Drop?) which display 340 scanlines. No problems on my PAL here.

 

So while some systems and setups are very tolerant, others can handle only minimal deviations.

[Omegamatrix]

If you make the off count scanlines less tolerant, then some games that are currently emulated while break. Some games have big jumps in scanline counts between there title screens and playing screens. I think Buck Rogers is one of them. The real problem is some TV's can't even handle being 1 or 2 scanlines off spec, while some TV's can handle it no problem. By spec, I mean the 262 scanline count we aim for on the 2600 for NTSC games.

 

 

I think the emulator should still be able to play games like Buck Rogers, Air Raid, and so on. When it comes to developing, it is really the responsibility of the programmer to use ALT-L to check their game.

[+stephena]

Fair enough, best to leave well enough alone. Besides, there's much more work to do in other areas ...

[Joe Musashi]

How about rolling the screen shortly only when the scanline count changes?

 

I recently had the problem that going from one kernel to another caused the number of scanlines go to 263 for a single frame (because of the initialization). I only saw it when I tried on a TV where it rolled for a split second.

 

Such a feature could be turned off by default, it would also not require a defined limit, just a scanline count change would trigger it.

 

Of course, for developers, Stella could just show a warning (and I think this is planned), but a shortly rolling screen would be much more fun. Though I would agree that this nothing which should have a high priority.