What's the optimal Overclock frequency?

[phipscube]

I've hacked my AES to run at 16MHz and 12 MHz via a switch. I've found that some games work ok at 16MHz, some have corrupted GFX. I currently only have 1 game that seems to benefit from overclocking, that is Fatal Fury 2. This runs with slight GFX glitches at 16MHz but is bearable.

I got thinking though, what if I try a lower clock. So I bought a 14 and 15MHz Osc.

At 15MHz there seems to be no difference. When running FF2, the boards in Jubei's stage seem to break with no slowdown in exaclty the same speed as at 16MHz. Nice and fluid.

At 14MHz, things get interesting. Samurai Spirits 2 suddenly works perfectly with no GFX glitches (its a nightmare of blocko-vision at 15 and 16MHz). And FF2 runs with no glitches at all.... the best bit? ... the boards in Jubei's stage break in exactly the same fluid way as at 15 and 16MHz....

So my question is, why do folks normally use 16MHz and not 14MHz?

I've only got a few games up to now so can't do a thorough test. I'm wondering how Metal Slug 2 would run at 14MHz compared to 16Mhz for example. I feel I don't want to give up my left lung just yet to be able to afford to buy it and test

Anyone tried to do a similar test with MS2?

 

[Xian Xi]

MS2 is a programming issue which causes the slowdown. Something like it only updates once per cycle but the game logic updates twice percycle and the graphics just try to play catch up the whole time. Don't get me wrong, it does become more playable when overclocked. MS2 I had runniing at 16mhz and made a little difference.

Most games you just get corrupt graphics but the slugs seem to handle it VERY well. I only tried the highest of 16mhz on the Slugs but I think X, 3, 4 and 5 can go a lot higher than 16mhz, maybe 20-24mhz but that's double the stock speed so I'd rather swap out the old CPU with an updated 68k that can handle faster speeds maybe a 16mhz model. Never tried it so let me know if you do.

 

[MCF 76]

My AES is overclocked with a switch just for Slug 2 I got a 16mhz speed crystal installed in it now, never tried the 14mhz crystal. But you have me curious about it now though Personelly its worth it and I can tell a big difference but, still stage 2 with the mummies slows down a bit, and stage 6 some also. >Marty<

 

[phipscube]

Thanks for the replies guys. I think there may well be little (if any) difference in "slowdown" between 14MHz and 16MHz if FF2 is anything to judge on. 14MHz runs the games i've tested so far with no glitches but still has the speed gains of 16MHz. I've only tested SS2, FF2 and Crossed Swords up to now though. I'll do more game tests when I get my Neo back home (its at work now with me whilst I try to repair my Sony 29" CRT "between jobs" ).

MCF 76, if you don't mind popping off your AES Hood, I have a spare 14MHz Osc I can send you to try. PM me if you want to give it a whirl. I think MS2 is the worst game for slowdown, so if you can test it @14MHz and 16MHz and see if there is any difference... If not, then 14MHz may be a better all round option when overclocking.

 

[Xian Xi]

Make sure you put a switch in so you can switch between stock and increased speeds.

 

[phipscube]

Yep, I already installed this it switches between stock speed and whatever Overclock Oscillator I put in. My Overclock Osc is socketed too, so I Can swap between 14, 15 and 16MHz (or any other if it comes to it, all only +5V of course) manually until I decide which one I want to stick with.

 

[MCF 76]

Thanks for the replies guys. I think there may well be little (if any) difference in "slowdown" between 14MHz and 16MHz if FF2 is anything to judge on. 14MHz runs the games i've tested so far with no glitches but still has the speed gains of 16MHz. I've only tested SS2, FF2 and Crossed Swords up to now though. I'll do more game tests when I get my Neo back home (its at work now with me whilst I try to repair my Sony 29" CRT "between jobs" ).

MCF 76, if you don't mind popping off your AES Hood, I have a spare 14MHz Osc I can send you to try. PM me if you want to give it a whirl. I think MS2 is the worst game for slowdown, so if you can test it @14MHz and 16MHz and see if there is any difference... If not, then 14MHz may be a better all round option when overclocking.

Hey man, I forgot to mention my AES has an OSC socket to interchange the speed crystal aswell. Jeff Kurtz did all the work to mine about 2 yrs ago. I live in TN, I was looking at your location on your profile earlier. I don't think it would be worth it to send it all the way over here. But we can if you wish to >Marty<

 

[phipscube]

Its no probs, it will only cost a few Krone. PM me your addy and i'll post it off to you FOC

 

[werejag]

so we determand 14mhz is best? i have mine overclockable to 15mhz right now

 

[phipscube]

I've only checked with Fatal Fury 2. But if thats is anything to go by right now, there is no diff between 14, 15 and 16MHz. The only thing is at 15 and 16MHz there are major glitches on other games that aren't there for 14MHz.

 

[werejag]

maybe we can build a variable oscillator

 

[phipscube]

Thats a good idea, if MS2 proves to run much better at 16MHz compared to 14MHz then its a viable option. Do you have any games with slowdown werejag?

 

[werejag]

i only own a few games 4.

i did the mod for anther guy and decided ill just do mine also.

i really cant afford any new games for a long while

i have plenty for mvs but only 4 for aes.

and i was told we have cheap converter but the guy decided to charge and arm and a leg so no Daedalus for me

 

[68k]

You need a switch.

The problem has nothing to do with the 68000 CPU itself, but in most cases the corrupt graphics are a result of ROM refresh or DRAM access being too slow.

You can't just overclock and be done with it. You have to be able to switch back to stock in order to play some games.

 

[werejag]

of course its switchable. i did say overclockable

 

[phipscube]

No probs werejag, i'm in the same boat regarding games. Long time Neo fan (Since I first played Magician Lord on an MVS back in 1990) but only decided to buy one 21 years later

68K, aye mate, i've got a switch in. But the debate here is if it might be better to use 14MHz instead of 16MHz in Overclock mode. Up to now Fatal Fury 2 works as good at 14 as it does 16, but there isn't any GFX corruption at 14MHz. If more games that have slowdown work in a similar fashion then it might mean 14MHz is a better option for overclock.

If anyone who has an overclocked Neo Geo and any notoriously sluggish games that could compare 14 and 16Mhz and post here if there is any difference, that would be great.

It might be that some games (Like FF2) don't need any more than 14MHz, some (like MS2) might need 16MHz. I'm just curious as to if anyone has actually tried to see if the jump from 14 to 16 is a worthy one.

 

[werejag]

im runing 15mhz when switched. the customer bought them and shipped and i kept the extras only reason why i choose 15mhz

 

[phipscube]

I've tested all the games I have, This is just for if Games have corrupt GFX or not. After each game name the descriptions are for GFX:- 14MHz, 15MHz, 16MHz. I played each game through the first stage.

Original BIOS: - OK, Corrupt, Corrupt
The Super Spy: - OK, OK, OK
Ghost Pilots: - OK, Corrupt, Corrupt
Ninja Combat: - OK, OK, OK
Magician Lord: - OK, OK, OK
Samurai Spirits 2: - OK, corrupt, corrupt
Alpha Mission II: - OK, OK, OK
Crossed Swords: - OK, OK, OK
Blues Journey: - OK, OK, OK
Fatal Fury 2: - OK, Corrupt, Corrupt

The only game that experiences gains is Fatal Fury 2 (as i've described in earlier posts). And these gains max out at 14MHz. The only thing 15 and 16MHz adds is GFX corruption.

The interesting thing is that ALL games run fine at 14MHz, no corruption (Even stock BIOS).

As I get more games i'll post results here as and when.