Re: [stella] Megacart Specs

Subject: Re: [stella] Megacart Specs
From: Glenn Saunders <krishna@xxxxxxxxxxxx>
Date: Mon, 13 Apr 1998 01:53:20 -0700 (PDT)
On Sun, 12 Apr 1998, Chris Wilkson wrote:
> I'm not sure how that guy works.  But I don't think it directly affects the
> graphics.  However, it might free up processor cycles, which would allow more
> time to do graphics stuff.  Can anyone enlighten me here?

>From what Crane said in his interview, I gather that the DPC chip acts
almost like a coprocessor, making simple repetitive calculations (like the
pointer example given) which would normally take a lot of CPU time away
during the display portion of the kernel.

These cycle savings can then be put to use in the form of more color
changes and changes to the sprites per scanline.

That's why Pitfall II almost looks more like an Atari 800 game than a 2600

The DPC chip could also be thought of as bridging the gap between the
all-software kernel of the 2600 and the all-hardware "display list" 
system of the Atari 800, as it provides some hardware support to take the
burden off of the software kernel.

The sound circuitry is a whole other animal.  The DPC chip is by far the
most elaborate piece of hardware designed for the 2600, more outlandish
than the Supercharger by far, and surely secures Crane's reputation as
the most amazing single individual in VCS history.

> Now that I think of it, I'm pretty sure that the Pitfall2 chip is a ROM
> chip, not RAM.  Therefore it is specific to Pitfall2 and couldn't be used.
> Maybe a POKEY could be added.  But again, not until Release 2 of the Megacart.

The DPC chip is a special custom chip, not ROM or RAM.  It was general
purpose and was meant to be used in more games than just Pitfall II.  The
crash prevented that from happening.

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