[atari7800] Re: Some questions..

  • From: "Andy Mucho" <m00@xxxxxxxxxxxxxxxxxxx>
  • To: <atari7800@xxxxxxxxxxxxx>
  • Date: Wed, 15 Sep 2004 10:23:37 +0100

I missed on on the whole CC2 thing :(
Still, somewhere around the house or loft I've got an original Atari devcard
from when I was writing StarBreaker on the 2600, but I've no idea where it
is, or if it's been lost in a move or something.. =\

My only thoughts were that possibly by writing to the zone list pointers, as
referred to in Maria Specds, to manually extend the screen for how ever much
I needed beyond the 512 byte memory constraint, by firing NMIs off at the
end of each extended zone then manually setting up the zone pointers for the
remainder of the extended screen..

The Maria Specs referred to separate Zone Pointers, and DL pointers, which I
was hoping the zone pointers could be "manipulated", but I can't find them
in the memory map..

Anyway, I'll forget about the longer DLLs for now, as it's not priority #1
right now :)


> -----Original Message-----
> From: atari7800-bounce@xxxxxxxxxxxxx [mailto:atari7800-
> bounce@xxxxxxxxxxxxx] On Behalf Of Eric Ball
> Sent: 15 September 2004 00:17
> To: atari7800@xxxxxxxxxxxxx
> Subject: [atari7800] Re: Some questions..
> I have my CC2 (way cool, thanks Chad), but haven't found the time to start
> using it for development.
> I'm fairly certain that there is nothing you can do to effect the DLL
> pointer during the frame.  The DPPL/H registers get latched at the
> begining
> of the frame to an internal working register.
> However, there is nothing that prevents you from having multiple DLLs in
> RAM, or creating one on the fly.
> As Dan said, typically each DLL handles 8 or 16 scanlines, using the same
> display list for each.  This minimizes the number of display lists requied
> (and thus the amount of RAM and the number of updates required to move the
> sprites around).
> From a demo I did last year - "The following is a rough guide: 2 cycles /
> RAM byte, 3 cycles / ROM byte, approx 400 cycles available per line."
> And if you exceed the number of cycles available, the 7800 just starts on
> the next line.

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