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Why the SNES mini emulates more than just the console

SuperFX and beyond: the extra custom hardware used in some of the system's greatest games.

The upcoming Super NES mini console is more than just a SNES emulator. Like its predecessor, it harkens back to a time where physical cartridges allowed for the integration of custom hardware on a per-game basis that would evolve the capabilities of the base hardware. The Super NES - or Super Famicom, if you like - took that to the next level, not least with the introduction of the SuperFX chip, bringing hardware-based 3D to the 16-bit era. The SNES mini features Nintendo's first ever official emulation of that chip, but SuperFX is just one example of custom hardware that improved the console's capabilities.

For starters, the SNES mini features emulation of two different SuperFX processors - as evidenced by the retro console's support for Star Fox, its sequel and Yoshi's Island. But it's not just the integration of the hardware that is fascinating - it's the implementation of it, and how Nintendo utilised the extra power alongside the console's native capabilities.

At the most basic level, the SuperFX chip is a 16-bit RISC processor with DSP functions. The original version ran at 10.74Mhz and enabled the system to perform the necessary calculations required for 3D. The chip does not feature any special hardware for rendering polygons, however, and instead relies on the programmer to write their own software rasteriser. Judged by today's standards, Star Fox runs at a very low frame-rate (we regularly encounter sub-10fps areas) but the game is designed well enough that it's still remarkably fun to play. The FX chip is used for most functions in the game.

We have full 3D objects with rotation and animation as well as point rendering, for stars and dots along the playfield, line segments for wire-frame objects and more. Filled, flat shaded polygons are used for most of the game's visuals while scaled sprites are used for objects such as asteroids. There's even light point-sampled texture mapping in spots. The primary limitations here are, of course, the low performance and the small display window.

In the latest episode of DF Retro, John discusses SNES mini: emulation, custom hardware, technical highlights in the library - and the games that should have made the cut.

Regarding the SNES Mini, this brings up the question of accuracy. It's very likely that the emulator will run the game at the correct speed and duplicate the experience as it was on real Super NES hardware. That's certainly the correct default way to play but is it the best way? Well-known console modder Drakon modified Star Fox to run overclocked at a much higher clock-speed. While the game is still capped at 20fps, the fluidity is massively improved resulting in a more playable game all around. Perhaps an option on the SNES mini for such an experience would be welcome? Unlikely, but you never know.

Then we have Star Fox 2. Near finished builds exist on the internet but developer Dylan Cuthbert has noted that these samples are not up to the level of quality present in later unreleased ROMs. This game uses the SuperFX 2 chip and displays more complex visuals and scenarios than the original game, thanks in no small part to a clock-speed bump to 21MHz. The chip was also tweaked to support higher capacity cartridges. It'll be fascinating to see how the final game shapes up, but the SNES mini also plays host to Yoshi's Island - another SuperFX 2 title, but one that used the additional horsepower in unique ways.

The faster RISC hardware was capable of so many different types of operations, and while Yoshi's Island does make use of polygons in select scenes, its usage is focused more on sprite scaling and rotation, among other things. The game is extremely heavy on special effects and animation. It's the kind of stuff that a stock SNES has no business pulling off and even compared to the consoles that would follow in its wake, Yoshi's Island looked and played beautifully. It also marks another first - until the SNES mini, Nintendo had never re-released the original Yoshi's Island on any other platform. If you wanted to play it, you were stuck with the Game Boy Advance conversion which, while not terrible, is a downgrade from the original in many ways.

While the SuperFX is the most well-known and heavily marketed additional processor, the practice was widespread on SNES and per-game hardware enhancements began very early in the console's lifecycle. Super Mario Kart, for instance, uses an NEC DSP chip referred to as the DSP-1 for its enhanced math coprocessor functions designed to speed up scaling and rotation operations. This title rightfully takes its place in the SNES mini line-up, meaning Nintendo has integrated DSP-1 emulation - but it's just a shame that Pilotwings (also using the same accelerator hardware) doesn't make the grade.

Other titles in the SNES mini line-up - Kirby Super Star and Super Mario RPG - also include the SA1 chip, a hardware upgrade designed to address one of the key limitations of the core console hardware: it's depressingly slow CPU. The SA1 contains a processor core based on the 65C816 16-bit microprocessor. Improvements include faster memory, a higher clock speed, and new arithmetic functions such as multiplication - yes, astonishingly the stock SNES CPU had no native multiplication function. Other included features concern upgraded memory mapping functions and new direct memory access modes such as bitmap to plane transfer.

In a sense, the SNES mini is much more than a console emulator then - it has to provide accurate representations of at least four other processors not found in the original console (SuperFX, SuperFX1, DSP-1 and SA1). If the console turns out to be as hackable and as expandable as its predecessor, support for these chips plus base emulation should cover off the vast majority of the system's library but for those interested in the full range of bespoke per-game hardware enhancements used in the SNES library, this article has you covered. It fascinating to see the range of functions - including very basic AI - that custom hardware was used for, often very sparingly. Hardware like the S-DD1 processor only manifested in two games (Street Fighter Alpha 2 and Star Ocean) and carried out real-time decompression of sprite data. It was an effort to break the hard limits of cartridge memory.

Of course, while additional hardware was widely utilised, the reality is that most games were released using support for the SNES's core capabilities - and there are a few titles in the SNES mini line-up that could have benefited from the enhanced CPU power of the SA1 at least. Games like Super Ghouls 'n' Ghosts deserve their classic status, but they are blighted by obvious slowdown - a factor of the slow CPU. That said, the visually lush Donkey Kong Country worked just fine using base hardware, albeit bolstered with the use of an extravagant 32-megabit cartridge.

The innovation here came exclusively from Rare's talented developers making the most of what they could. Yes, the introduction of sprites and tiles rendered on an SGI workstation was impressive at the time, but it's the other ways in which Rare used the hardware that really stand out. For one thing, there's copious amounts of line scrolling in many of the stages with a rich parallax effect that wasn't always common on the Super NES. Lighting and transparency effects are also used often creating a unique atmosphere, with colour palette shifts beautifully representing a shift in the time of day.

The water segments were also impressive: the subtle ripples, rich parallax backgrounds and great colour usage really gave the impression of swimming deep below the water. The mine stage is another triumph - swinging lights use the transparency function to create atmosphere while the light cones themselves use rotation to gently swing back and forth. There are all sorts of great tricks like this. Even without the use of custom hardware, Donkey Kong Country would stand as Super NES technical showcase - and that's before we've even factored in the stunning David Wise soundtrack.

And that leads us onto an aspect of the Super NES's core capabilities that was remarkable without any need for additional hardware - its sound module. Which brings us to one of the more unique aspects of the Super NES - the sound module. Composed of the Sony SPC700 8-bit CPU alongside a DSP unit with associated memory, SNES titles were capable of some remarkable results. Until this point, games consoles typically relied on chips with digital noise generators, FM synthesis or a mix of the two often with an additional PCM channel or two. The programmer could use this hardware to produce unique and interesting sounds. This could result in some amazing sounding games when done right.

The Super SNES, however, relied on sampled audio - basically pre-recorded digital samples along with basic noise generation. The SPC700 and DSP could then add basic echo and reverb and generally modulate these samples into what you would hear during the game. The system could play back eight channels simultaneously and was limited to just 64KB of memory. As a result, composers and programmers often battled with memory trying to cram as much sample and program data in there as possible. Samples were often stored at a very high pitch, which required less memory, then pitched down and filtered by the hardware. Sound effects were often created by using pitched instrument samples. All of this was played back at 32khz.

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What does this all mean then? A very different style of audio compared to other gaming machines of this era. Contra 3 - included on SNES mini - showcases just how strange it can get. The tunes are catchy enough but not in the traditional NES style: these are complex, layered tracks, while Castlevania 4, another Konami effort, featured a more ambient score than previous games in the series. Other examples of awesome audio on the SNES include Earthbound, with its super strange Hirokazu "Hip" Tanaka soundtrack.

All of which returns us to the hope that emulation accuracy on the SNES mini is improved over its NES sibling, which wasn't quite on the ball in some areas, particularly in terms of audio reproduction. We also hope to see improved scaling for modern displays on the new unit, and hopefully support for 1080p video output, to eliminate what could potentially be two sets of scaling before the image hits your display. But overall, we just can't wait to see the return of some classic console software in an irresistible form-factor - while there are some glaring omissions from the title line-up, the overall roster is strong overall, tapping into quality and nostalgia in equal measure. The response to the announcement has been overwhelmingly positive - let's just hope that Nintendo has learned lessons in terms of delivering enough stock to satisfy demand. Suffice to say, when the finished units are available, Digital Foundry Retro will be there with a full, detailed review.

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