Super FX proper overclock

Includes but not limited to: SNES, Genesis, Sega CD, PlayStation 1, Nintendo 64, Dreamcast, Game Gear and I guess the Virtual Boy.

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Joined: Sat Dec 06, 2008 8:22 am

Super FX proper overclock

Post by Drakon » Sat Oct 15, 2011 9:03 am

Here's the original and ever so popular superfx overclock by marshallh: ... 80&start=0

This mod doesn't overclock anything...I tried this mod and I got games to either underclock or just match the original speed. Even using a 200 mhz 2 pin oscillator the game ran at the same speed as when it was connected to the original ceramic resonator. I guess this's another great example of how people will believe any hype. Sure the game will still run fine after you do this mod but it won't run any faster than it used to.

Thanks to a great idea by robivy64 I found a way that actually does work. After robivy posted a picture of his overclocked starfox cartridge I noticed that in the picture he wasn't using a 2 pin crystal like the marshallh mod. I pmed robivy and asked him what he used on that cartridge. He said he just used a 4 pin crystal oscillator feeding a clock signal into the input trace that winds up going into the mario chip. I then decided to take a good long hard look at my various superfx pcbs. Indeed my mario chip starfox cartridge has the 21.4 mhz clock pin on the cartridge connector almost directly wired into the mario chip clock pin. There's only what looks like an inductor between that pin and the mario chip. You can bypass this inductor and the chip runs fine. So this made me realize that you can feed a clock signal straight into a mario chip and it'll work fine.

The gsu 1 and gsu 2 pcbs have the clock circuit built onto the cartridge pcb for some strange reason. I wired up a 4 pin crstal oscillator to vcc and ground of the cart. I next disconnected the clock trace of the superfx chip from the original clock circuit and wired it directly into my crystal oscillator clock output pin. The game ran no problem first time and finally you could tell that the game was indeed overclocked.

Here's what I've learned from experience.

The gsu 1 and mario chip aren't worth overclocking. When these chips are overclocked and there's not a lot to draw you indeed get a much improved framerate. However once you go to an area in the game where the chip has to draw a lot of things you get slowdown that's just as bad as when the chip is running at normal speeds. This makes sense considering that the mario chip is just a beta version of the gsu 1.

The gsu 2 is the only chip I recommend overclocking. This chip doesn't slowdown nearly as much as the gsu 1 / mario chip. Also the gsu 2 can overclock much higher than the gsu 1 / mario chip. The downside to this is I had to find gsu 2 donor cartridges and swap out the surface mount maskroms for maskroms of my favourite superfx games. Also in the case of stunt race fx you need a battery saving circuit for the game to work and doom doesn't have the battery circuit on it. Therefore the only donor cart you can use for stunt race fx is winter gold which also requires you to change the surface mount region chip since it was a pal only release. As far as I can tell surface mount region chips for the snes were only used on superfx pcbs. On a more positive note you can swap out maskroms of superfx carts with each other and this works fine so unless you're making a starfox 2 cartridge you don't need to bother burning an eprom.

The first starfox has the overall game speed increase a little when you overclock the game, but it's still perfectly playable. Luckily both starfox 2 and doom the gameplay speed was exactly the same when I overclocked these cartridges. The only difference was that the framerate greatly improved.

Different games have different speeds that they can run at without crashing. Here's my list so far:

Starfox: 28.322 mhz is the fastest I got this game going at without it crashing

Doom: Also 28.322 mhz

Starfox 2: 33 mhz

Here's my description of how to do this mod:

If anyone wants to try this for themself here's the technique.

1: Find the clock trace on the superfx chip, it connects to a hex inverter chip and a ceramic resonator.

2: Disconnect the clock trace from everything.

3: Wire up a 4 pin crystal oscillator of your desired speed to vcc and ground.

4: Wire the clock signal output pin of the oscillator to the clock trace on the superfx chip

I hope you found my post both educational as well as stimulating :P

Posts: 46
Joined: Sat Dec 06, 2008 8:22 am

Re: Super FX proper overclock

Post by Drakon » Sun Jan 08, 2012 10:04 am

Me and doug stumbled across a way to get starfox 1 running even faster:

I hope this's enough evidence to satisfy most hardcore trolls that I actually do know what I'm doing and talking about.

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