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: Manuel Polik <cybergoth@xxxxxxxx>
Date: Sat, 10 Nov 2001 12:55:18 +0100
Hi Eckhard!

>This is an answer to the messages of Thomas, Andrew and 

So I'll pick my part to answer to :-)

>> Ok, after I stopped paniking, I probably found a 
>> & 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 
>switching between 261 and 262 lines, the new binary 
>a stable 262 lines. So I think it should work alright 
>a real system.

Phew. Fine. Passed another hurdle :-)

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

This might happen, since I'm just jumping into the reset 
routine, not really caring where I'm coming from.

What does this behaviour do to the TV picture? A little 
one-frame-jump or something more severe? (Does it look 
unprofessional? :-))

>> 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. 

Aha. Most. So I'm better gonna do a proper PAL picture? 

But... #1

>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, 
>> 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 
>Then you could see the difference. You are probably 
>the gameplay doesn't really feel different. But maybe 
>could adjust the lenght of the notes for the song, to 
>the same playing speed as in the NTSC version?

Hm... the same speed would be next to impossible, since 
the music is driven once per frame.

But really, the speed of the music is more or less 
happening by accident anyway, by some weird 
constellation of processor MHz + some power-of-2 timers 
per frame, so it doesn't matter if the PAL one is 
slower, since there isn't any *right* speed anyway. 
Maybe a slower PAL music is coming even closer to the 
original Johnny Cash timing? One is Johnny Cash live, 
the other is the studio recording, I don't know and I 
don't (want to) care :-)

#1 ...wouldn't a 262 lines PAL colored cartridge have 
the same running times as the NTSC one, i.e. play the 
music at the same speed? (Please say yes, or I fear my 
picture of the world is crumbling to dust...)

If yes, so how many XX% of TVs are 'most'?
Is any PAL game sold with only 262 lines and was there 
any negative feedback so far?

What should I do?

My own TV can display 50/60 Hz too, but I experienced a 
flickering picture on a few NTSC cartridges as well. And 
I really don't want someone else to pay 16$ + shipping 
around the globe for a catridge that doesn't work...

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

Ok, I'll defintely will fix this, when doing a full PAL 

My favourite solution at the moment would be doing that 
fix by shifting another 20 lines from the overscan to 
the VBLANK, optimize the music tables for NTSC and 
ignore any frequency differences and the 50/60 Hz 

This'd produce a stable picture on both versions and I'm 
sure that both PAL and NTSC people will get used to 
*their* version.


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