Super FX Chip | Code Like It's 198x

In 1993 the Super Nintendo drew a 3D space battle in filled polygons, and the hardware that did it came in the box with the game. The Super FX was a graphics processor designed by the London company Argonaut and mounted on the circuit board of the Star Fox cartridge, so a player got the extra power by buying the game, not an add-on. It shared the cartridge’s memory with the console, ran several times faster than the console’s own processor, and did the one thing the Super NES picture hardware could not: put a pixel at a coordinate. Before the chip, Edge reported in 1998, the game had run at one frame a second.

Fast facts

What: a Graphic Support Unit (GSU) in the game pak: a RISC-style processor with sixteen 16-bit registers and a 512-byte instruction cache. The instructions used most are one byte long and run in one cycle from the cache. PLOT, COLOR and RPIX handle pixels, alongside the usual loads, stores, arithmetic and branches.
First name: the MARIO chip, for Mathematical Argonaut Rotation I/O. Early Star Fox boards carry chips marked “MARIO CHIP 1”.
Clock: 10.74 MHz in the first version, which Nintendo’s manual calls “six times as fast as the Super NES CPU”. A clock-select flag lets later chips run at 21.4 MHz; the magazines called that version the Super FX 2.
Memory: no program ROM of its own. It runs from the game’s ROM and draws into the cartridge RAM, both shared with the console’s CPU.
Designers: Argonaut Software. The patent, filed in January 1992, names Jeremy San, Ben Cheese, Carl Graham and Peter Warnes as inventors.
Games: Star Fox (1993), Stunt Race FX and Vortex (1994), Dirt Trax FX, Dirt Racer, Yoshi’s Island and Doom (1995), and Winter Gold (1996).

Where it came from

Jez San told the story to Edge in 1994. Argonaut had built “a prototype of the Starglider game, which we called NESGlider”, after its 1986 polygon game Starglider. “We showed it to Nintendo and they said this is really cool, we like the technology, and we’d like to see you do something on our new machine. So they gave us an early SNES machine, and within a week we’d ported NESGlider onto it.” He gave Super Play the date in 1993: “Our original idea was to do something not unlike the Super FX chip, but actually for the NES. This was back in 1990, before the Super Famicom had even been released in Japan”. Argonaut “were given a Super Famicom back in June 1990, which was about six months before it went on sale in Japan.” That July, at a round-table of 3D programmers in ACE, San said: “Every hardware designer I meet I ask to put a polygon chip into their next machine. One day they will.”

Nintendo judged NESGlider “a bit too ‘cult’”. San: “To get a 3D game to appeal to people you have to spend time introducing them to the 3D concept and easing them in gently, which is of course the whole idea behind StarFox. We limited your movement to more or less straight ahead.” The division of labour, in his words: “we did all the technical stuff and all the technology and we designed the chip, but we learned a lot from Nintendo about how to write mass market games.”

San told Retro Gamer in 2006 that Nintendo “jumped at the chance and financed the creation of the MARIO chip (Mathematical Argonaut Rotation I/O chip), which was designed by Rob Macaulay and Ben Cheese … and was later renamed Super FX”. The chip and the 3D software were developed in England, with James Hakewill also on the hardware and Carl Graham and Pete Warnes on the 3D software, while Dylan Cuthbert, Krister Wombell, Giles Goddard and later Colin Reed worked on the game in Nintendo’s offices in Kyoto. The patent Argonaut filed on 30 January 1992, granted in 1995 and now held by Nintendo, names San, Cheese, Graham and Warnes as its inventors.

What it does

The Super NES draws its backgrounds from 8×8 characters, not from a bitmap. A program that wants to plot a point, draw a line or fill a polygon has to build the result as character data before the picture chip can show it, and on the console’s 65816 processor that conversion is slow. Nintendo’s Development Manual for licensees calls the Super FX’s answer “bitmap emulation”. The PLOT instruction takes a coordinate and a colour and writes the pixel into character data in cartridge RAM. The chip can lay the result out as a background 128, 160 or 192 dots high, or as an array of sprites, and the console’s CPU then copies the finished frame into video memory.

The two processors run in parallel but take turns with the memory. The manual says they “can not access either simultaneously”: a flag set by the console’s CPU decides which side has the cartridge ROM, and another the RAM. While the Super FX has the ROM, the console cannot even read its own interrupt vectors from it, so the chip answers those reads with dummy vectors that point into the console’s work RAM at $0100–$010C, and the program has to keep its interrupt handlers there. The 512-byte cache lets the Super FX keep running its inner loops while the bus is busy; the manual says code is read from it “six times as fast as reading from game pak ROM or RAM”. A cycle table published by the SuperFamicom.org wiki shows the difference: an ADD takes three cycles from ROM or RAM and one from cache.

The instruction set shows what the chip was for. Next to the basics sit FMULT and LMULT, multiplies for the fixed-point sums of 3D rotation, and PLOT, which takes anywhere from 1 to 48 cycles from cache in the same table, depending on what it has to do. There was an electrical cost too. The manual requires a Super FX game to check which accessories are plugged in and to halt the chip if it finds, for example, the Multi Player 5 adaptor, because together they “would exceed the maximum current rating” of the console’s power supply.

Nintendo Power explained the idea to its readers in January 1993: “The Super FX is what engineers and programmers call a RISC which stands for Reduced Instruction Set Computer. What it does in simple terms is to make a lot of very specific types of calculations very fast”, like a kicker who “could boot it through the uprights 100% of the time from as far away as 100 yards, and he could do it 60 times a second!” Super Play compared it to the “RISC technology, as found in the Archimedes home computers”, and San put its speed at 3D polygons and texture mapping as “faster than a 286 PC, and about on a par with a 386 PC”.

Announcement and Star Fox

Game Informer carried the announcement in September 1992: “Nintendo of America Inc., announced the launch of their Super FX custom chip … based on RISC technology and includes digital signal processor functions. The result is new features such as texture mapping, shading and real time 3-D perspective. Nintendo’s first cartridge utilizing the new chip is anticipated to reach the shelves by February 1993.” Nintendo Power promised “games in which you can move about freely in a real time 3-D universe”, then in January 1993 named the game: “Nintendo’s Star Fox will be the first game to make use of the custom Super FX chip. Since the chip itself is buried inside the Game Pak, the only evidence of this miniature marvel will be on the screen.” Its advantage over Mode 7 was that “not only can large backgrounds be rotated … but even sprites can be manipulated individually”, and “polygons are the most impressive of rotating images, however, because you can spin them around any axis for a true 3-D effect.”

The chip had a price. Super Play reported that it had “boosted the cart price to 9,800 Yen (approx £40)” in Japan, and saw Star Fox at the Consumer Electronics Show inside a dome, “the Argonaut developed 3D shoot-em-up which is the first game to use the new Super F/X chip”. San described the split of the work: “the 3D maths routines and the basic game engine – was done by Argonaut, both here in the UK and also by some of our guys who are working at Nintendo’s HQ in Japan”, with character and spaceship design by Nintendo under Shigeru Miyamoto. Edge put the game’s sales at four million copies in 1998.

The faster chip

Nintendo’s manual describes a clock-select register: with its flag at 0 the Super FX runs at 10.7 MHz, with it at 1 at 21.4 MHz. Edge went to Argonaut in April 1994 “to set the record straight” on this Super FX 2, then due in Stunt Race FX (“originally called XLR8”) and Elite’s PowerSlide: “The Super FX2 operating system is rated at 21.477MHz (one instruction per cycle, so 21.477 Mips), and can generate between 5,000 and 10,000 polygons per second (a 30% increase over the first FX chip). It has also been seen to handle up to 32,000 small triangular polygons per second in complex shapes.” Nintendo Power called it “twice as fast as the chip that was used in StarFox” in February 1995, and named Stunt Race FX and Vortex as the games that had used it so far.

The chips themselves carry different names. According to public accounts of the boards, the earliest Star Fox cartridges hold a “MARIO CHIP 1” that divides its 21.47 MHz input clock in half, later revisions marked GSU-1 run at the full speed, and the GSU-2 and GSU-2-SP1 can address a ROM larger than 8 megabits.

Edge also compared the chip with Sega’s SVP, the processor in the Mega Drive Virtua Racing cartridge: “the Super FX supports all SNES screen modes: 4, 16 and 256 colours, whereas the SVP only has 16 colours … while Stunt Race FX … runs at about the same speed, it’s actually doing twice the processing to run in 256-colour mode.” And on cost: “The SFX also has no built-in masked ROM; it contains purely task memory so it runs its program from the same ROM the game does. Different games merely need different ROMs; you don’t need to change the SFX chip.”

The games

Only eight games with the chip came out during the Super NES’s lifetime. Nintendo Power admitted in January 1996 that “Super FX games just aren’t common enough”.

Star Fox (Starwing in Europe), Nintendo and Argonaut, 1993.
Stunt Race FX, Nintendo, 1994: polygon cars and tracks in 256 colours.
Vortex, Argonaut, 1994, published by Electro Brain in America and Sony in Britain. Nintendo Power called Electro Brain “the first licensee to make a Super FX game”, and Nintendo Magazine System said Vortex had “some of the most complex 3D in any Super FX game”. San told Edge in 1998 that it “played really well, but obviously it didn’t sell as well as Star Fox”.
Dirt Trax FX, Sculptured Software for Electro Brain, 1995: polygon tracks with sprite motorbikes, and a two-player split screen that Nintendo Power said needed “the raw power of the Super FX”.
Dirt Racer, Elite, 1995: Edge called it “the second SFX offering from Elite” after PowerSlide.
Super Mario World 2: Yoshi’s Island, Nintendo, 1995. It used the chip for sprites rather than polygons: “Just about all of the bosses in Yoshi’s Island take advantage of the Super FX chip,” Nintendo Magazine System explained. “This means that they’re unusually big and daunting while not suffering any horrid slowdown.” Nintendo Power credited the chip with “the huge bosses and morphmation effects”.
Doom, Sculptured Software for Williams, 1995. Nintendo Power reported that Sculptured was “working with Williams and id software” on it, and Super Play said it “needs the help of a Super FX Chip” for its 3D levels.
Winter Gold, Funcom, 1996, a winter-sports game in polygons. “The Norwegian developer, Funcom, used the FX chip to power Winter Gold.”

Others were shown and never released on the Super NES at the time. Elite’s PowerSlide was one. Nintendo Power previewed Argonaut’s polygon fighting game FX Fighter in February 1995, alongside a Super FX Comanche built on NovaLogic’s voxel landscapes, which Edge had called “another unimpressive Super FX game”. Star Fox 2, on the faster chip and “now a simultaneous two-player one”, was finished but held back; Nintendo released it in 2017 on the Super NES Classic Edition.

The cartridge-chip family

The Super FX was one of several processors Nintendo licensed into game paks; an Edge reader in 1995 listed “a DSP from Nintendo and Seta, the SFX chip from Argonaut and now the ACM from Rare”. The cartridge entry describes the others. The polygon chip San had asked every hardware designer for ended up in the cartridge rather than the console, and it opened the way for Argonaut’s later business selling processor designs as ARC.

Sources

Nintendo, Super NES Development Manual, Book II (licensee-only, 1993–1995), section 2 (Super FX): chapter 1, features, the 10.74 MHz clock, the 512-byte cache, sixteen 16-bit registers, shared ROM and RAM, and the accessory current limit; chapter 4, the clock-select register (10.7 or 21.4 MHz); chapter 5, the ROM and RAM access flags and the dummy interrupt vectors; chapter 8.1, bitmap emulation.
SNESdev Wiki, “Super FX” (web, secondary): 14 general-purpose registers, 98 instructions. https://snes.nesdev.org/wiki/Super_FX
SuperFamicom.org wiki, “Super FX cycle times” and “Super FX opcode matrix” (web, secondary).
US Patent 5,388,841, “External memory system having programmable graphics processor for use in a video game system or the like”, filed 30 January 1992, granted 14 February 1995. https://patents.google.com/patent/US5388841A/en
ACE issue 34, July 1990: the 3D round-table (“a polygon chip”).
Game Informer issue 6, September 1992: the Super FX announcement.
Nintendo Power issue 42, November 1992: “Nintendo has announced two major innovations for 1993”.
Nintendo Power issue 44, January 1993: the Super FX feature and Star Fox.
Super Play issue 4, February 1993: Star Fox news, the cartridge price, and “Special F/X chips” (the Archimedes comparison).
Super Play issue 5, March 1993: the CES report.
Super Play issue 7, May 1993: interview with Jez San by Jason Brookes and Matt Bielby.
Super Play issue 16, February 1994, and issue 17, March 1994: Starfox II on the faster chip.
Edge issue 7, April 1994: the Super FX 2 figures, the comparison with the SVP, PowerSlide and Dirt Racer, and the interview with Jez San.
Nintendo Power issue 63, August 1994: Elite’s two Super FX racing games; Electro Brain and Vortex.
Nintendo Magazine System issue 26, November 1994: Vortex review.
Super Play issue 26, December 1994: Vortex (Sony, Argonaut).
Nintendo Power issue 69, February 1995: the Super FX 2, Star Fox 2, FX Fighter, Dirt Trax FX and Comanche.
Edge issue 18, March 1995: Shoshinkai report (Starfox 2 and Comanche).
Edge issue 23, August 1995: reader’s letter on cartridge chips.
Edge issue 26, November 1995: Doom for the Super NES at ECTS.
Nintendo Magazine System issue 40, January 1996: Yoshi’s Island and its bosses.
Nintendo Power issue 80, January 1996: Yoshi’s Island; “Super FX games just aren’t common enough”.
Nintendo Power issue 72, May 1995: Doom by Sculptured Software for Williams.
Super Play issue 42, April 1996: Doom and the Super FX.
Nintendo Power issue 84, May 1996: Winter Gold.
Edge issue 33, June 1996: Star Fox “coded in the UK by Argonaut”.
Edge issue 62, September 1998: “Audience with Jez San” (the one-frame-a-second Star Fox, four million sales, Vortex).
“The Making of Starfox”, Retro Gamer issue 28, 2006: the MARIO chip and the teams in England and Kyoto.
“Argonaut Games”, Wikipedia (web, secondary): Star Fox 2’s release in 2017. https://en.wikipedia.org/wiki/Argonaut_Games
“Super FX” and “List of Super NES enhancement chips”, Wikipedia (web, secondary): chip revisions and the list of released games. https://en.wikipedia.org/wiki/Super_FX