JOTEGO

Why not a single core for all CAPCOM pre-CPS games?

Added 2019-09-02 14:00:03 +0000 UTC

As I said in twitter, all pre-CPS CAPCOM are so similar we could call them CPS0. However, this is more a statement about design principles followed by the engineers than about the actual hardware.

Most of these games have exactly the same screen resolution, generated by the same pixel counters. Most of them have character and background tile sets, controlled in almost the same way. Most of them will have two CPU's communicated via an 8-bit latch. Most of them use 2xYM2203 for sound. Most of them have very similar memory maps. Most of them have a sprite DMA circuit (which MAME thinks is a watchdog!).

But some games have M6809 CPU's, others Z80's others M68000. Some games have special hardware to drive the background tile map directly from a map ROM. Some games have 3 bit per background pixel, whereas others have 4 bits. Some games use palette PROMs in many places, others only at the colour mixer, others don't use them at all. Some even have variable sprite length. Some have no tile map hardware but others have two background planes. Some have memory banks for CPU code. Others don't. Some even have a third CPU for extra sound processing. Some have encryption or even a microcontroller to act as a copy protection device.

Indeed the variation is very large around a common CPS0 theme, which is why I think we will have many FPGA cores, albeit some of them capable of running more than one game.