RE: [stella] Help (Timing problems?)

Subject: RE: [stella] Help (Timing problems?)
From: Nicolás Olhaberry <nolh@xxxxxxxxxxxxx>
Date: Mon, 2 Aug 1993 06:47:42 -0300
----- Original Message -----
From: Erik Mooney <erik@xxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Monday, July 30, 2001 11:17 PM
Subject: Re: [stella] Help (Timing problems?)

> Unless I'm missing it, you have no loop to wait for the end of VBLANK
> (should look like Wait: LDA TIM64T / BNE Wait).  The emulators will
> forgive that and start displaying on the PC screen as soon as you write
> the zero to VBLANK, but a real TV on a 2600 video signal won't.

Hi to all! Thanks to Erik for answering my last question.

Since the subject of frame construction has been touched, I want to know if
really is important to follow the 3 VSYNC, 37 VBLANK, 192 DISPLAY, 30
OVERSCAN programmers guide recomendations. At first I thought I would be
important for a correct display to follow these guides, but a lot of games
doesn´t do that.

Here are a few examples, I´m always refering to NTSC versions:

Alien: Doesn´t even use a whole line for VSYNC, just 22 cpu cycles, and 73
lines for VBLANK (that seems way too much for NTSC, but the game uses less
than 200 lines for display, so...).

Combat: Uses 42 lines for VBLANK and slightly more than 200 lines for
display after that.

Math Grand Prix: Uses almost 2 lines for VSYNC and 40 for VBLANK.

Superman: Uses 6 lines for VBLANK. And VBLANK is started 3 lines before
VSYNC, and finished right after the end of VSYNC.

And there a lot more games like these, so, how important is all this for a
proper frame display on a T.V. set?



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