A Quest For the Perfect SNES Emulator

An anonymous reader sends this excerpt from the Opposable Thumbs blog: "It doesn't take much raw power to play Nintendo or SNES games on a modern PC; emulators could do it in the 1990s with a mere 25MHz of processing power. But emulating those old consoles accurately — well, that's another challenge entirely; accurate emulators may need up to 3GHz of power to faithfully recreate aging tech. ... As an example, compare the spinning triforce animation from the opening to Legend of Zelda on the ZSNES and bsnes emulators. On the former, the triforces will complete their rotations far too soon as a result of the CPU running well over 40 percent faster than a real SNES. These are little details, but if you have an eye for accuracy, they can be maddening. ... The primary demands of an emulator are the amount of times per second one processor must synchronize with another. An emulator is an inherently serial process. Attempting to rely on today's multi-core processors leads to all kinds of timing problems. Take the analogy of an assembly line: one person unloads the boxes, another person scans them, another opens them, another starts putting the item together, etc. Synchronization is the equivalent of stalling out and clearing the entire assembly line, then starting over on a new product. It's an incredible hit to throughput. It completely negates the benefits of pipelining and out-of-order execution. The more you have to synchronize, the faster your assembly line has to move to keep up."

Comments

Chipsets

[WorBlux]

Isn't the chipsets used just about out of patent, and thus allowing perfect emulation by including a copy of the chips used on a USB device?

Re:Chipsets

[AmiMoJo]

Latency on USB is terrible. It just isn't designed for that sort of thing.

The problem that the summary alludes to is context switching, changing from one task to another. Every time you do it you have to save data from one task to memory and reload data for the next one. Most operating systems do that and it isn't a problem when you are only switching 1,000,000 times per second even for a fairly low end console.

Amiga emulation was thought to be nearly impossible because of this, but some clever chap realised that you can do a fairly close approximation and get a reasonably good result while running at the speed of the original machine. TFA doesn't make it clear but I think what it is trying to demonstrate is how the CPU can end up running too fast because in an actual SNES the other hardware causes wait states for memory access and the like which effectively slows it down. Say the CPU wants to access video memory but the graphics chip also needs to use it. Since the graphics hardware can't wait (it would cause corruption on the display) it gets priority and the CPU has to wait instead. The delay is handled internally by the CPU so there is no hint in the game's code that this is happening and a traditional emulator would not take account of it.

Re:ZSNES is perfect

[FhnuZoag]

Haha, yes. I can't wait for the new wave of emulators that make you blow on your hard drives before your roms will work.

Hz != Power

[Anonymous Coward]

3GHz is a measure of frequency, not power. Words mean things, use them correctly.

Attention to detail, or games will crash

[iYk6]

You seem to be missing the point. The triforce spinning was probably a bad example, since it's not that important. The problems with inaccurate emulators range from annoying visual glitches, to crashes, to actually making a game unbeatable. Star Ocean, for example, will sometimes crash in zsnes, but I haven't experienced that in bsnes. The battles run at double speed, much like the triforce in LTTP. Playing Yoshi's Island in zsnes, any level with those giant fuzzballs will tick every time you move. It's nauseating to get through. In zsnes, Super Mario RPG battles will sometimes de-sync to the point that the music and animations will continue, but your input will no longer work and you have to reset the game.

In Speedy Gonzales - Los Gatos Bandidos, if you're playing with zsnes, you can't even beat the game, because it doesn't emulate everything necessary to do so. In Sink or Swim, the room fills with water, and you need to swim above it. But because of timing and speed issues, the room fills up much too fast and you will drown instantly.

You can read about some of these issues, and many more, here: http://byuu.org/bsnes/accuracy

Re:ZSNES is perfect

[ObsessiveMathsFreak]

Well, there is a difference. Here's a ZSNES emulation of the LTTP intro, which you can compare with the Speed Demos Archive run. SDA don't actually accept emulator runs, so the video there is from an actual SNES.

Now, the TAS videos run doesn't display the same problem, but that was probably run from Snes9x, not ZSNES(technically from a custom Snes9x build supporting re-recording). So the issue is not the processing power required but simply the fact that the Snes9x and ZSNES developers focused on different features.

Overall, it can be seen from all three videos that in general, a good emulator can emulate the underlying hardware with extremely high fidelity for the vast majority of games and gameplay.

Fidelity isn't a burning issue in modern 8 or 16 bit emulation. Emulators are now literally concerned with advanced features like recording, "rewinding", and video and audio filters that actually improve the games graphics and sound beyond what the hardware was capable of. The only outstanding feature I personally feel is missing from most emulators is cross platform support.

Re:ZSNES is perfect

[genner]

The real question is: When will we have a JavaScript emulator ?

It's called the Opera browser. It's runs JavaScript but it's not quite the real thing.

Re:Is there an actual article here?

[Hatta]

Some guy? Byuu is the author of the finest emulator yet created. He's not asking a question because he knows the answer. He's speaking from his own expertise.