Sunday, 10 May 2015

Capcom CPS1 - Part 2

Welcome to the second post in the Capcom CPS1 reverse engineering series, you can find Part 1 right here.

The roots of CPS1

Everything we know has an origin and predecessors, Capcom's arcade platform CP System 1 is no exception to the rule.

For many years arcade manufacturers battled for market share in release cycles that saw games burning out of distribution in just a few months. This intense competition demanded manufacturers faster releases and better games in a never ending market race.

According to an interview by LCSM to Kouichi "Isuke" Yotsui, father of Capcom's hit title "Strider", the Capcom Play System (CPS1) was originally developed with the need to bring better and bigger graphics into new games.

Isuke: "PCBs back then did not hold an abundant amount of data for graphics. The CPS was developed to free ourselves from that."
Isuke circa 2011. Source: Striderpedia

With full 16 bits capabilities, plenty of hardware sprites, tiles and graphic layers, CPS1 extended game asset and code storage capacity beyond its lifetime needs. No game ever released on CPS1 used the 4 megabytes of rom capacity found in the system.

The availability of the new system sparked the production at Capcom of a new generation of games developed almost in parallel. The three initial titles under development consisted in Daimakaimura (Ghouls'n Ghosts), Forgotten Worlds, and Strider, in that order respectively. In the end Forgotten Worlds made it first to market and got to be the first official CPS1 release title.

The Chocolate Factory. Capcom's production line, circa 1992. credit: Super Power magazine


But how did CPS1 and its specs came to be? An early 1990s interview extract from the french magazine "Super Power" seems to confirm the prevalent expert arcade community opinion: CPS1 base specs came straight from a computer commercially unknown to the western world: Sharp's X68000 a.k.a. the god computer.

Isuke: “I have participated to the development of the CP system and yes absolutely, the X68000 is the base of the CP system." (Thanks to Denis Lechevalier for the interview extract and photos)
Capcom offices. Circa 1992. credit: Super Power magazine


X68000: The God Computer

In March of 1987 Sharp released the X68000 home computer to the Japanese market, a multimedia computer so strong and powerful it had no immediate rivals. The new system wasn't even matched by the highly awarded Commodore Amiga 500 released six months later.

Sharp X68000

The X68000 featured full 16 bits capabilities thanks to its Motorola 68k cpu running at 10Mhz, came with 1 megabyte of memory upgradable to 12 megabytes, advanced sound and high resolution hardware graphics with a 65k color palette, a device better than any arcade game platform at the time. Full specs.

Personally whenever I try compare the X68000 with the humble specs of my first computer back then, the Amstrad CPC 6128, I really feel the X68000 earned its "god computer" nickname well. Indeed a device sent from the future.

With the introduction of the X68000 Sharp leapfrogged the market in such a way it remained the most capable gaming platform until the early 1990s. Even today the X68000 with its distinct double tower design is still undeniably appealing in terms of aesthetics. PS4 anyone?

With a whopping price tag of 369,000 Japanese Yens, $2,434 USD in 1987 money or more than $5000 USD in today's money, Sharp sold millions of units in the Japanese market until its final update in 1993. The reasons as to why Sharp didn't release this system outside of Japan are unknown to me, please contribute any information by commenting below.




According to what is known, Capcom used the X68000 as a benchmark for its CPS1 hardware design and also as game development workstation. Capcom wasn't the only arcade game design company known to have used the X68000 for the production of videogames, for example Toaplan used it to develop games like Outzone, Truxton, and all of their 68000 based releases.

Capcom's sound and music design team at work. X68000 compact workstation. Super Power magazine.

Thanks to its involvement in content and game creation and its strong market share, the X68000 enjoyed plenty of pixel perfect arcade ports. Titles such as Final Fight or Daimakaimura (Ghouls'n Ghosts) were released on the X68000 and are still in high demand by todays collectors. Ironically, putting your hands today on a copy of Final Fight for the X68000 will cost you twice as much as the original arcade game board.

Although commonly referred as a pixel perfect port, ports like Final Fight aren't exactly perfect. For example Final Fight for the X68000 will only display a maximum of four concurrent enemies on screen where as the arcade version will do as many as nine. This is due to CPS1 being more capable in terms of hardware sprites: 256 vs 128.




The Chocolate Factory Suppliers

Now we know how Capcom got its base specs for the development of CPS1. How about hardware suppliers?

Many companies contributed to the making and supply of CPS1 parts, although one particular company contributed the most significant number of them. Hitachi, the Japanese multinational, was the most notable supplier with multiple parts including TTL chips, memories, and the main system CPU.

Capcom's CPS1 featured the CMOS version of the Motorola 68000 CPU running at 10Mhz (later upgraded to 12Mhz). The CPU introduced in 1985 was a joint development of Motorola and Hitachi after a long term relationship between the companies.

This special relationship was recently discussed in an interview with Bill Walker, a now retired SVP at Motorola:
"Our manufacturing practices were pretty bad back then, low yields, long cycle times and poor productivity. In 1978, Motorola and Hitachi entered into a technology exchange venture. We brought a lot back and injected it into our manufacturing and it helped greatly, especially when we built our newest factory in the early eighties. That became the factory that built most of the 68K products – a new 5 inch factory, MOS-8."
The original CPS1 main cpu: Hitachi Motorola 68000 2-micron CMOS process

Other significant parts found inside CPS1 boards are the secondary cpu dedicated to running the sound program, a standard Z80 type cpu by Zilog running at a speed of 3.5Mhz, or multiple rom chips sourced from a variety of vendors such as Intel, AMD, Hitachi or Sharp.


The Graphic Customs

One of the most intriguing questions we had at the time of starting the reverse engineering effort on CPS1 was identifying who developed the two mysterious customs found on the A and C boards. None of them showed any identifiable manufacturer marks or logos besides the CAPCOM mark and production id numbers.

CPS1 custom chips, B custom on the left, A on the right.

In our mind the most probable vendor responsible for these customs could had been Hitachi, not only we knew it to be a high contributor to CPS1 parts, but also at the time of the making of CPS1 Hitachi had a good number of popular custom ASIC products in the market.

Uncovering the custom secrets and helping the arcade community overcome the popular CPS1 security issues led us to begin the reverse engineering efforts on these customs. Once digshadow got his hands on the CPS1 parts I sent him the wait to understand who was behind the customs came to an end. At his lab and with the aid of a powerful metallurgical microscope the truth got revealed: the vendor of choosing for the CPS1 custom parts was Ricoh.

Partial photo of CPS-1 custom B-21 under the microscope, credit: digshadow

This finding went against all our bets, but research revealed Ricoh was in the business of producing a range of CMOS based products including memory products and gate array or standard cell based custom chips. According to specifications found in Ricoh's 1988 product databook, both custom chips found in CPS1 belong to the RSC-15 CMOS standard cell series made with a 1.5 micron process.

[Update May/13th 2015] Thanks to everyone who pointed out Ricoh is the company behind the original Nintendo NES cpu, a variant of the popular 6502 cpu. More on this here.

Thanks to this integration effort Capcom introduced plenty of new graphic hardware functions packaged inside these customs, and managed to substantially reduce overall pcb complexity by eliminating legacy parts used in previous designs.

With them also came a number of security measures that have been a nightmare to today's arcade collectors and a barrier to fully preserve a good number of arcade titles in the CPS1 series.

This is all for now, I hope you have enjoyed Part 2 of the CPS1 reverse engineering series. On the next post we will explore custom B-21 in detail and discuss how the custom chip got dissected and analyzed. Stay tuned.

Update: Part 3 now available