Re: Z26, VSYNC, Timers, somebody HELP ME! (was: Re: [stella] Gunfight Release Candidate(s))

Subject: Re: Z26, VSYNC, Timers, somebody HELP ME! (was: Re: [stella] Gunfight Release Candidate(s))
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Fri, 9 Nov 2001 17:00:00 +0100
This is an answer to the messages of Thomas, Andrew and Manuel.

> Are the values between NTSC and PAL different?

The TIA changes the sound output twice per scanline, and the
PAL VCS operates at a slightly slower clock frequency than
the NTSC one. So the sound frequencies are a little differerent
between both consoles as well. But I don't think it's bad enough
to make it nessessary to change the sound effects in a game.
BTW, z26 and the other emulators don't do the exact frequency
of either console, so there might some marginal differences
in the sound as well.

> When I have some extra time I will give that a try (but the little free
> computer time I have seems to all be sucked up feeding bits to the
> box sitting next to my computer).

If you don't do it, nobody else will. And then we all will have
to live with visually imperfect versions of your games. ;-)

> Is there any plan to port z26 to Windows. It's a great program (especially
> the log feature) but as a DOS program, the performance under Windows XP is
> little disappointing.

Weeelll, John and I have been thinking about that for quite a
while now, and we even found someone who is willing to do all
the Windows interfacing code, so that we can concentrate on
porting the emulator core. But that person is currently very
busy with his job, John is very busy with his move, and I can
easily make up an excuse too, if I have to. ;-) So unless one
of us eventually buys a new computer with XP on it and gets
dissatisfied with the performance of z26 as well, it might
still take quite a while before we'll be able to present a
usable version of gz26 for XP. ;-) (Did anyone actually get
that joke on the emulator/OS name? ;-) )

> Ok, after I stopped paniking, I probably found a simple
> & suitable solution. Can someone please test if the
> attached NTSC bin produces a stable picture on a real
> NTSC TV/VCS combination for me?

I don't have a NTSC VCS, but I implemented the scanline
display in z26, and while the old version was constantly
switching between 261 and 262 lines, the new binary does
a stable 262 lines. So I think it should work alright on
a real system.

One think I noticed though, when the game ends and the game
jumps back to attract mode, it seems to be skipping a VSYNC
and does a double-frame or something like that. Maybe you
should have a look at that code again.

> If I get that right, you want me to use the same line
> numbers in both versions?

> So it is supposed to work on a PAL TV, when ~70 lines
> are just missing?

This is correct. As Andrew has already mentioned, most
PAL TVs should be able to display this nicely. The screen
will be centered, so you'll get black bars above and below
the picture. But that's what your normal PAL version should
do anyway. BTW, it's exactly 50 lines that the PAL VCS
screen is longer than the NTSC VCS screen. ;-)

> Hm... in all my (Mega Drive / Super NES) experiences, a
> difference between 50/60 doesn't make any difference,
> neither in sound nor in gameplay.

You should run the PAL version with the -5 switch in z26.
Then you could see the difference. You are probably right,
the gameplay doesn't really feel different. But maybe you
could adjust the lenght of the notes for the song, to get
the same playing speed as in the NTSC version?

> My train of thought was like this:
> - The manual says do 38 PAL VBLANK lines.
> - I wanted to keep 192 visible lines.
> - Now I thought I've to add all the missing scannlines
> to the overscan.

This is basically correct, but if you do this, then the
picture will start at the top of the TV screen. And since
you are displaying less scanlines than you should for
a normal PAL picture, you'll get all thos blank lines at
the end of the display. This doesn't look too nice.

Ciao, Eckhard Stolberg

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