SpiceWare's Blog

Ok, now I'm confused. I thought DPC was the chip in Pitfall 2, but here it seems to be a sophisticated bank switching mode. The ARM is the extra processor on the Melody boards, right?

DPC

a co-processor chip created by David Patrick Crane. It speeds up things like the drawing of players, making it possible to draw a multicolored player(sprite) in 14 cycles instead of 26 (there's only 76 cycles per scanline, so freeing up 12 cycles allows you do additional updates on each scanline, resulting in a better looking game). Adds ability to use one of the Atari's voices to do in-game 3 voice music, leaving the other voice free for sound effects. It was used for Pitfall II. It can do a number of other things, like line drawing, which weren't used in Pitfall II. It would have been used for additional games, but the console market collapsed*. In Pitfall II the game uses bankswitching for 8K. It's probable that later DPC games could have used more ROM, we don't know. There's an additional 2K of graphic data that can't be directly accessed by the 6507, the DPC co-processor must be used to hand that data over to the 6507.

 

DPC+

An updated version of DPC. It speeds things up even more - that 14 cycle multi-color player(sprite) is now down to just 10 cycles. Takes away the "unused features" and replaces them with new ones, like the ability to manipulate the graphic data (in DPC the data is in ROM, in DPC+ it's in RAM). The bankswitching ability was expanded to 24K, the Graphics Data was expanded to 4K. The ARM chip emulates the DPC+ co-processor, just like it emulates the DPC coprocessor if you use a Harmony/Melody to play Pitfall II.

 

The ARM only needs to work as the co-processor when the visible portion of screen is being generated. So we added the ability to call ARM code during Vertical Blank and Overscan. You don't have to use it, but the ARM's a 70 MHz 32 bit CPU so it's able to do significantly more calculations than the Atari's 1 MHz 8 bit CPU.

 

*A big part of that was home computers had just become affordable in the USA - my friends and I all put away our consoles and were gaming on our new home computers.

 

 

In spite of that, work was progressing on another holiday game - one that I hope will bear fruit (hehe) in the future.

I've posted an update on my profile, but no good news.

That's a bummer

Sorry to hear that, Zach. I enjoyed collaborating on projects with you. Hope we can do it again sometime.