Sat. Oct 1st, 2022

A stock Gradius III ROM running without delay? The new version of bsnes makes it possible.

When it comes to emulator design, there’s something to be said for trying to capture the workings of the original system as accurately as possible, with warts and all. But there’s also something about the idea that emulators can improve on the original hardware, eliminating issues like frame rate lag that plagued the underpowered processors of the time.

Which brings us to the latest update to the legendary accuracy-obsessed SNES emulator bsnes, which adds the ability to overclock the virtual SNES processor. While bsnes is far from the first SNES emulator to allow simulated overclocking, it appears to be the first to do so “without any framerate or tone distortion, and without compromising compatibility in 99% of games,” as bsnes programmer byuu places it.

Fast, but not too fast

Most SNES games were locked at a frame rate of 60 fps, and designers of the time tuned their games so that the SNES hardware could maintain that frame rate. But in some in-game situations, when the screen became too crowded with moving sprites, the processor was unable to capture the next frame within the 16.66 ms window, leading to noticeable display lag.

Today’s chunky PCs can, of course, simulate the SNES’s Ricoh 5A22 CPU at a speed much faster than the original 3.58MHz. But because the system’s games are designed with that particular clock speed in mind, that kind of overclocking tends to speed up the video and audio as well, which in turn can make the games difficult or impossible to play (or even run,). in some cases).

To remedy this side effect, byuu borrowed a technique from elsewhere in the emulation community. “For years, NES emulators had an overclocking method that added extra scanlines for the CPU for each video frame,” byuu tells Ars Technica. That is, only the CPU runs a little extra time after each frame of video is rendered, but the video and audio don’t… This new(ish) overclocking method gives games more processing time without also speeding up video and audio speeds. .. and so the normal game rate of 60 fps is maintained.”

The result, for most standard SNES games, is the complete removal of the infamous frame rate slowdown that showed up when too many sprites clogged the screen. Byuu has posted side by side video samples showing how this improvement extends into Contra III and Gradius III

(Emulators may remember a lag-free version of Gradius III which was released in May. But while that version required extensive hardware and software hacking, the bsnes edition should work on most SNES software without modification.

There are some limitations to this new overclocking method, mainly due to the many enhancement chips of SNES cartridges. “SuperFX games are kind of a special case,” says byuu. “Because they tend not to run at 60fps due to the demands of software that rasterizes entire screens on the SNES, the game logic is designed around the frame rates. So even if you accelerate StarFoxthe game engine will now seem to be spinning too fast.”

SuperFX games like StarFox animate smoother with overclocking, but gameplay also gets noticeably faster.

You can see this side effect in this comparison video of the SuperFX title StarFox† While the game animates much more smoothly with overclocking enabled, the gameplay also gets noticeably faster, adding to the game’s jittery challenge.

“I suppose you can think of SuperFX as older 80286 DOS games that run way, way too fast on modern PCs,” he continued. “It’s like they don’t have Vsync and just run as fast as possible. This new overclocking technique can’t really solve that: if you speed up the game, the game logic works faster. But in most cases, you might assume that they are more like modern games that rely on Vsync to maintain a consistent, smooth framerate.”

Limitations aside, we’re excited to have yet another example of an emulator that actually improves on the original game classics we remember. We will be happy to add this new overclocking solution with HD Mode 7 smoothing, widescreen NES games, controller lag mitigation and 4K upscaling for low-end HD games.

List image by Smile, Citrus

By akfire1

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