Model 2 | Code Like It's 198x

In 1994 an arcade driving game borrowed its looks from military flight simulators. Sega’s Model 2 board, which made its debut with Daytona USA, painted its polygons with texture-mapping chips from the American firm that built simulator graphics for the defence industry, first as part of General Electric and then of Martin Marietta and Lockheed Martin. “As defence spending has been cut, we decided to take our technology into the arcades,” that company’s marketing manager told Edge in 1995. A year earlier, one of Daytona’s creators had told the magazine that the game “throws 300,000 texture-mapped and shaded polygons around every second”. “Enough to knock anyone’s socks off,” Edge added.

Fast facts

Partners: Sega and General Electric Aerospace, from August 1992; the GE division passed to Martin Marietta, which merged with Lockheed in 1995.
First game: Daytona USA, shown finished at the AOU show in Tokyo in February 1994.
Main processor: a 32-bit RISC CPU at 25 MHz, Intel’s i960.
Throughput: 300,000 textured polygons a second, against about 180,000 untextured ones on Model 1.
Display: 496×384, 65,536 colours from a 1,024-colour palette.
Revisions: Model 2A-CRX, 2B-CRX and 2C-CRX.
Successor: Model 3 (1996), built on Lockheed Martin’s R3D/PRO-1000.

How it was built

Sega’s first polygon board, Model 1, ran Virtua Racing and Virtua Fighter with flat, untextured shapes. For the next board, Yu Suzuki, head of Sega AM2, told Edge in June 1994, the offer came from the other side: “General Electric Co. approached us because they had realtime texture-mapping ASICs [application-specific integrated circuits] and we entered a commercial partnership with them in August 1992. We co-developed the Model 2 board with them over a period of a year, and Daytona GP took a further year to develop.” Daytona GP was Edge’s early name for Daytona USA.

Edge later told a less tidy story. Sega’s own engineers, it reported in October 1995, had “failed to make significant progress towards an advanced texture-mapping version” of Model 1, so the American company “was called in to lend assistance”. The group sat in Daytona Beach, Florida, “across the street from the Daytona International Speedway”, and had already worked with Sega on Model 1. After that board was finished Martin Marietta bought GE Aerospace, and in 1995 Martin Marietta merged with Lockheed. In Edge’s summary, Model 2 was “a combination of Sega’s Model 1 polygon engine technology and a Martin Marietta-designed texture-mapping board”. The American side supplied the texture-mapping chips and its TARGET system for building 3D databases.

How it draws a frame

The work is split between a host and a graphics part, as Edge explained for arcade image generators in general: a “host” that “basically runs the game”, working out collisions and telling the graphics hardware where to put the polygons, and a graphics part that draws the scene. On Model 2 the host is the 25 MHz 32-bit RISC processor in Edge’s 1994 specification, which MAME, the arcade emulator, identifies as Intel’s i960KB. Beside it sits the geometry engine, listed by Edge as a “3D matrix” coprocessor, which rotates and projects each shape’s corners; MAME’s emulation uses Fujitsu signal processors, the TGP, on the first boards. The Sega and Lockheed Martin rasteriser then fills each polygon with texture. Alongside the polygons, two scrolling layers of flat tile graphics come from the design of Sega’s older System 24 board.

Edge‘s specification box lists what the board could do to a polygon: flat shading, texture mapping, “micro-texture” and two reflection modes, one “spread” and one “mirror”. Suzuki picked out the reflection of the sky in the cars’ windows, “all handled in hardware by separate algorithms”. He was also open about what Daytona left out. It “only uses Gouraud shading in the attract sequence — the actual game uses flat shading, which is much faster”. Shading the whole game smoothly would, he thought, have made it “between three and five times slower”, and he was “pretty sure Ridge Racer has been programmed in the same way”. Asked whether Model 2 beat Namco’s System 22, the board behind Ridge Racer, he answered: “Personally, yes.”

Daytona USA

Edge saw Daytona at 5% complete in its April 1994 issue. Its source put Model 2 at 300,000 textured polygons a second and Model 1 at “about 180,000 plain polygons”, and promised up to eight players in linked cabinets. Suzuki had wanted more: “Originally, I had wanted to have 40 cars linked up, just like in a real race, but it just wasn’t feasible.” At the AOU show in February, Sega linked 13 cabinets together, and Edge reported that the first reaction was that the game was “better than Ridge Racer”. The spec box gave Daytona 178 of the board’s maximum 248 megabits of ROM.

The gap between the board and a home console showed a year later, when Edge previewed the Saturn version. In the arcade, “Daytona’s dedicated graphics processors generate an amazing 5000 polygons per frame, every 1/60th of a second”. AM2 was aiming for 30 frames a second on the Saturn, with each car “around 160 polygons”, and the coin-op’s “crisp 496x384 display”, its micro-texture and its reflections would all be missing.

Virtua Fighter 2 and Virtua Cop

At Japan’s Amusement Machine Show late in 1994, Sega showed two more Model 2 games. Virtua Fighter 2 ran “at 60fps (twice the speed of the original)”, and Edge learned that the board used for it “has been speeded up and now includes extra memory, enabling the screen to draw further into the distance. This was one of the most noticeable problems that Daytona USA suffered from.” AM2’s Virtua Cop, a light-gun game, had “fantastic Model 2 visuals which put it way ahead of the pack”, though some observers called it “Lethal Enforcers with polygons”.

2A, 2B and 2C

The board was revised three times, and MAME’s emulation sorts the games by revision. The original Model 2 ran Daytona USA, Virtua Cop and Desert Tank, the last credited jointly to “Sega / Martin Marietta”. Model 2A-CRX, with Sega’s SCSP sound chip in place of the Model 1 sound board, ran Virtua Fighter 2, Sega Rally, Virtua Cop 2 and Manx TT Superbike. Model 2B-CRX replaced the Fujitsu geometry processors with Analog Devices SHARC signal processors and ran Virtua Striker, Fighting Vipers, Cyber Troopers Virtual-On, Indy 500 and Last Bronx. Model 2C-CRX used Fujitsu’s newer TGPx4 and ran Sega Touring Car Championship, The House of the Dead and Top Skater.

The period press was looser with the names. Edge described Indy 500’s board as “Sega’s enhanced Model 2B board (first seen in Sega Rally)”, and Sega Saturn Magazine said Sega Touring Car pushed “the Model 2B arcade graphics board to its limit”. Some games needed more than one board. Virtual-On’s designers told Edge in 1996 that two players on separate monitors needed “two Model 2B boards”, and an optional spectator screen “uses one more Model 2 board”. Sega also sold the hardware to other companies: Tecmo’s Dead or Alive, Psikyo’s Zero Gunner and Jaleco’s Super GT 24h all ran on Model 2 boards.

Model 3

Suzuki was already naming the successor in June 1994: “the only one I can mention is Model 3. Compared to Model 2, this is a very high-performance board.” It was late. In October 1995 Edge reported that Indy 500 had been “originally targeted for Model 3, but delays in the board’s progress meant it was coded up for Model 2 instead”, and that the new board “has little in common with its forerunner”: it was based on Lockheed Martin’s R3D/PRO-1000 rather than Model 1’s engine. Virtua Fighter 3 made its debut on it in 1996.

Model 2 carried on beside it. Sega’s AM3 team, interviewed by Sega Saturn Magazine in January 1998 about The Lost World, drew the line between the boards: “Model 2 is okay for Virtual stuff like robots and zombies”, but living creatures needed Model 3’s colour texture maps. Virtual-On’s robots and The House of the Dead’s zombies were both Model 2 games. Nor could code simply be moved across: “The Model 3 has a different Operating System (OS) to the one we used for the Model 2. We use a Windows ’95 package for the Model 3.”

Sources

Edge issue 7, April 1994: Daytona prescreen (300,000 texture-mapped polygons, Model 1’s 180,000, eight linked players).
Edge issue 8, May 1994, p. 8: AOU show report (Daytona USA finished, 13 linked cabinets, “better than Ridge Racer”).
Edge issue 9, June 1994, pp. 45–49: “Yu Suzuki: Sega’s driving force” (the General Electric partnership, the Model 2 specification box, reflections, flat and Gouraud shading, System 22, 40 linked cars, Model 3).
Edge issue 15, December 1994, pp. 11 and 31–32: Amusement Machine Show report (Virtua Cop) and Virtua Fighter 2 prescreen (60 frames a second, the faster board with extra memory).
Edge issue 19, April 1995: Saturn Daytona USA prescreen (5,000 polygons a frame, 160-polygon cars, 30 frames a second, the missing effects).
Edge issue 22, July 1995, p. 11: Lockheed Martin’s Real3D (the texture-mapping chips and TARGET for Model 2; Carlton Caldwell on defence spending and the arcades).
Edge issue 24, September 1995: Indy 500 on “Sega’s enhanced Model 2B board”.
Edge issue 25, October 1995: Saturn 2 news feature (GE Aerospace in Daytona Beach, its work on Model 1, Martin Marietta and Lockheed, Sega’s stalled texture-mapping work, host and graphics hardware, Model 3 and the R3D/PRO-1000, Indy 500).
Edge issue 30, March 1996: Cyber Troopers Virtual-On interview (two Model 2B boards and a third for the spectator screen).
Edge issue 37, October 1996: Virtua Fighter 3 prescreen, Model 3.
Sega Saturn Magazine issue 12, October 1996: Sega Touring Car Championship and “the Model 2B arcade graphics board”.
Sega Saturn Magazine issue 27, January 1998: AM3 interview on The Lost World (Model 2 and Model 3, the operating system); House of the Dead developed by AM1 on Model 2.
MAME source code (web, secondary), src/mame/sega/model2.cpp: the i960KB host, the TGP, SHARC and TGPx4 geometry processors, the Sega/Lockheed Martin rasteriser, the System 24 tilemaps, the sound hardware of each revision and the games assigned to each. https://github.com/mamedev/mame