RE: [stella] VBLANK or VSYNC first?

Subject: RE: [stella] VBLANK or VSYNC first?
From: Nicolás Olhaberry <nolh@xxxxxxxxxxxxx>
Date: Mon, 29 Oct 2001 23:07:47 -0300
> 1. The docs all show VSYNC as the top of the frame (3 lines) and then 37
> lines for VBLANK.  So isnt the scanline counter reset when VSYNC is
> to, not when it is turned off?  Doing it as you suggest would be 3 lines
> too late, yes?

You can restart the counter when VSYNC is turned on or off, it´s just a
matter of taste, you´re gonna have those 3 lines either way (at the start or
at the end of the frame). Anyway, since those lines will not display
anything, is not really important.

> 2. What is the beam counter actually used for?  Only for reference?  If I
> understand it, RSYNC controls this, but RSYNC seems hardly ever used :/

The TIA handles all the horizontal sync internally, but if you want to write
an emulator, you have to do it yourself, of course. A few examples: you
increment the scanline counter until the horizontal counter reaches 228,
another... when RESP0 is written to, you use the counter to know where in
the scanline is going to be displayed, etc... As you can see, you´re going
to use it all the time ;-)



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