9MHz Overclock

Discussion in 'Mega Everdrive / Everdrive MD' started by lnx64, Dec 26, 2012.

  1. APE

    APE Site Supporter 2015

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    And what if you use a halt switch to overclock it after the game starts running?
     
  2. lnx64

    lnx64 Robust Member

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    Booting isn't the problem. I can still boot at 10mhz. What I was even trying to do was flash at stock speed, turn off system, switch to overclock then turn back on.

    I didn't get enough switches to have a halt switch.
     
  3. MottZilla

    MottZilla Champion of the Forum

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    Again it is not a surprise if flashing/reading from the SD card doesn't work properly when using altered clock timing.

    About "rated speed", that means little to nothing. The Genesis was designed for the clock rate the CPU normally has. When you alter the timing of the CPU or other components there are a lot of things to go wrong. One thing to consider is the communication between the Z80 and the 68000. If the 68000 is running extremely faster than its stock 7.5mhz or so, but the Z80 is still running at the stock speed, communication with the Z80 may fail to work properly. There are other possible issues that could crop up when you overclock. Some games I've seen videos of overclocked clearly run faster than originally intended. The Sonic 3D Blast intro for one isn't speed throttled on its own, so when overclocked it plays too fast.

    If you have an increase from stock to exactly 8.0mhz I wouldn't expect much of any benefit. The 10.0mhz overclock videos I've seen seem to suggest a marked improvement with the best compatibility with software. But it's still best to have a switch for the speed and perhaps a halt switch too. If you need more switches order them. Don't just do a poor rush job. You'll regret it later on.
     
  4. lnx64

    lnx64 Robust Member

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    I don't order parts since there's a surplus store I get them from.

    But either way, I knew the over clock was going to have issues, but once again, I was only concerned for the EverDrive itself. Something people just aren't "reading". I got the answer, and the answer was-the menu wouldn't appear. But it did appear.

    I know the 68000 is rated for 8MHz. I know why SEGA chose not to use 8MHz, it was cheaper to share the clock with the YM2612. However, I did NOT expect to see graphical glitches at even 8MHz.

    As far as batman and robin, I'm 80% certain it's not using the Z80 for anything and is just sitting idle. So Z80/68000 communication I doubt is the issue here. I think the issue is the SEGA I/O controller used. I know it's not RAM, as I installed faster SRAM (not that it'll matter anyway) into my Genesis just for shits and giggles.
     
  5. wingzrow

    wingzrow Member

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    I'm the guy APE is modding the Genesis Model 1 for. Off hand I remember little things improving in the few games I tried when he overclocked my X-Eye.

    Sonic CD: No slowdown when sonic runs up the first vertical ramp
    Chakkan: All the random lag disappeared
    Viewpoint: Entire game is suddenly playable. One of the best games to test out an overclock on.
     
  6. Barone

    Barone Active Member

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    ???

    Which part of "This is not true in all cases." you didn't understand? I'm not forcing any general rule. Feels like we're discussing for nothing.


    Feels like you didn't read and/or comprehend what I said. I *specifically* mentioned the right model and it surely wasn't applicable for model 2 Genesis.
    Anyway, forget about it. I really didn't want to start a discuss with you or something. I just wanted to give the proper info.



    These are the ones that I can easily remember:
    Lotus II RECS ---> Runs significantly faster, closer to the original Amiga version.
    Super Hang-On (you must use Rev00 rom; the older one) ---> Runs significantly faster, closer to the arcade sensation.
    Streets of Rage ---> Removes the slowdown when you have the screen filled with enemies.
    Crude Buster/Two Crude Dudes ---> Removes the slowdown when you have the screen filled with enemies.
    Double Dragon II ---> Removes the permanent slowdown.
    Mega Man: The Wily Wars ---> Removes the permanent slowdown.
    Sonic Spinball ---> Removes the permanent slowdown and makes the scrolling significantly smoother.
    Zero Tolerance ---> Reduces the permanent slowdown making the game a lot more playable.
    Air Diver ---> Runs significantly faster, doesn't look choppier anymore.
    OutRun ---> Removes the slowdown when you're overtaking cars but do NOT speed up the game like in Super Hang-On 'cause it's limited to 20 fps in software (several other games fall into this category, like: After Burner II, Galaxy Force II, OutRun 2019 (this one has no noticeable slowdown but it's limited to 20 fps in software as well), etc... I'm trying to hack these games to change the way they limit the frame rate but it's not a easy 10 minute hack).
    MK3/UMK3 ---> Reduces the slowdown during combos and the permanent slowdown when fighting against/with Smoke.
    WWF Wrestlemania: The Arcade Game ---> Reduces (10 MHz)/Removes (12 MHz) the permanent slowdown when you're fighting against 3 other wrestlers.
    World of Illusion ---> Removes the permanent slowdown in one of the later levels when playing co-op.
    Psycho Pinball ---> Keeps the scrolling smooth using the faster speeds and reduces/removes the slowdown in multi-ball mode.
    F-15 Strike Eagle II ---> Reduces the permanent slowdown making the game a more playable.
    F-22 Interceptor ---> Reduces the permanent slowdown making the game a lot more playable.
    ...

    There are dozens more of games which benefit from the overclocking. Some don't benefit due to having the frame rate limited in software, like X-Men 2: Clone Wars in co-op mode (the frame rate is forced down in order to keep it consistent).
    In several games the 10 MHz overclock is not enough to remove the slowdown, like in Zero Tolerance, MK3/UMK3 combos and most of the 3D Genesis games. In such cases, the 12 MHz is a welcome extra boost.



    It really depends on a lot things, like the firmware revision of Everdrive MD and the Genesis model you're using.
    In my case I can boot and flash the games using the 12 MHz clock with no problem, but most of my previous reading had indicated that the halt switch was a must... The overclocking job on the Genesis is still no documented enough to determine all the exact problems you'll get with each specific Genesis/Mega Drive model, oscillator, wire length, etc...
    Some people have successfully OC'ed their Genesis using just an external Oscillator. In my case I couldn't get a stable signal, no matter how short the cables were cut. It might be due to the cheapo oscillator I was using? IDK. In my case, a Schimitt trigger solved the problem. For other people with similar difficulties the Schimitt trigger had no effect...


    I think it's more related to hardware than software. Most of the Genesis/Mega Drive models can't handle the 12 MHz overclock properly, so people had mistakenly reported such issues as game incompatibility problems, but that's not the case for most of the games.
    I have tried dozens of Genesis games and most of them will have no problem with either clock. My friend who has recorded the comparison video has gotten the very same results in terms of stability/compatibility with both 10 and 12 MHz clocks.


    Exactly. No overclock, even a 5% one, will work with either add-on according to my tests.


    It's better to get an oscillator rather than a crystal, otherwise you'll need to implement your own oscillator circuit using it and it will just add one more variable of bad luck in your circuit IMO.
    For some people things work right in the first try, for others it gets a lot of work in order to get it running properly. And have seen several guys giving up after trying "everything" and getting just glitches/freezing all the time. Of course, having good soldering skills and some experience with electronics always help; which wasn't my case.


    Just complementing: https://www.youtube.com/watch?v=cqAOjp3MlGA



    I didn't put words in your mouth, neither I intended to say you're trying to hide anything... Please, forgive me if it sounded like that.
    It's just that this subject had already raised some bad interpretations previously in this forum; I was just covering my ass from any misinterpretations this time, nothing else.
    If I intended to attack you or something, I'd not even cared to reply to this thread. ;)
     
    Last edited: Dec 29, 2012
  7. lnx64

    lnx64 Robust Member

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  8. sonicdude10

    sonicdude10 So long AG and thanks for all the fish!

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    So from what I'm getting in this thread is that the Everdrives do work with overclocks. You just need to have them set on stock speed for flashing the games in. And compatibility with overclocked systems also depends of what version and revision Genesis/ Megadrive you have.

    Am I following correctly?

    I wanna know before I go getting oscillators so I don't be wasting my monies on this...

    My plan is a tri-speed setup. Stock, 10, and 12.

    Do it to my model 3 first since I've already modded it to be completely region free with single 4 position switch.
     
  9. APE

    APE Site Supporter 2015

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    Sure, you did mention the model 1 specifically and I follow what you mean. But I was looking at the bigger picture which encompassed the model 2 and model 3 to a lesser extent. As someone who performs these mods for people I try to think as broadly as possible.

    It would be somewhat amusing to overclock the Sega PAC for my Laseractive but I don't think it'd be necessary or a good idea. On the off chance I broke it or somehow the CPU fries I'd rather not be out a rather expensive, and rare, piece of hardware.


    Sounds like you've got it right. I don't have much experience running model 2s beyond 10mhz as I've always used a crystal for this purpose but from what I've read it seems like they're more finicky than model 1s. The last "Genesis" I installed an overclock mod for was a JVC X'EYE and it took very well to 10mhz. The BIOS didn't like booting into 10mhz at all and with a halt switch the ability to properly use it was hit or miss.

    I'd imagine the success rate overclocking the Genesis' 68k while playing SegaCD games would be largely dependent on the game and how it uses the hardware. Booting directly into 10mhz was an issue for the X'EYE but the X'EYE is made out of some really crappy parts.
     
    Last edited: Dec 30, 2012
  10. lnx64

    lnx64 Robust Member

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    I can now flash games on the Everdrive at 10MHz just fine.

    Use Genny 3 mode. Works great.
     
  11. Druidic teacher

    Druidic teacher Officer at Arms

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    x
     
    Last edited: Jun 22, 2017
  12. lnx64

    lnx64 Robust Member

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    Well don't forget, there's only so many sprites the VDP can draw. ;) So it's probably got a shit ton drawing, but you can't see it.
     
  13. smf

    smf mamedev

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    Everything shares the same clock on the genesis, it's all derived from a ~53mhz crystal. Feeding the 68000 a signal that is not synchronised will cause bus issues, which is possibly why some of the games don't work. As they used an 8mhz 68000, the closest they could get was dividing it by 7. You might get better results by dividing the clock by 5.
     
  14. lnx64

    lnx64 Robust Member

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    Everything does NOT share the same clock signal. The Z80 isn't, it's running at a different speed than the rest of the hardware (3.58MHz). So that point is invalid. I'm aware it's all coming from one master oscillator. That wasn't the point I was making at all.

    But the YM2612 is supposed to run at 7.6MHz to have correct sound pitch. So instead of having another divider to get the 68k at the 8MHz it's rated for (and yes, the CPU's all have it stamped right on them -P8 meaning 8MHz), running it at 7.6MHz was fine enough for the time, considering the games that were coming out then. It still kicked the NES's ass.

    Why would I modify how the clock is being divided? The problem isn't the 68k talking to the YM2612, which is the only other component on the board that shared the clock of the 68k. There's other factors here, glue logic, VDP, etc. And you're not going to easily get around those limitations either. It's just how those chips are. Some board revisions are better than others.
     
  15. sonicdude10

    sonicdude10 So long AG and thanks for all the fish!

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    Reason that works is because "Genny 3 mode" uses an internal clock to determine the speed of transfer from SD card to SRAM. Standard mode uses a clock signal from the Gennesis to make the flashing a bit faster. So running overclock speeds must speed the bus up beyond what the SD card, CPLD (FPGA?), or something else in there can handle.

    Am I right? Evidence and knowledge seems to support that theory ATM...
     
  16. lnx64

    lnx64 Robust Member

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    I'm sure it's probably the FPGA that can't handle it, not the SD card. It already reads and writes too slow.

    I usually use Genny 3 mode anyway, very reliable.
     
  17. MottZilla

    MottZilla Champion of the Forum

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    smf is not a random nobody so I wouldn't discount what he's saying so easily. From what I gather he says there is a 53mhz clock on the board which different components get a divided rate from, but the clocks are synchronized even though the division is giving them a different clock rate. He's suggesting that instead of using a divider of 7 for the CPU to use one of 5 to get 10.6mhz rather than introducing a new clock signal generator that I'm guessing won't be in step with the other clocks. Hopefully he'll comment on exactly what. I wonder how hard it would be to change the divider.
     
  18. lnx64

    lnx64 Robust Member

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    I'd rather not implement a clock divider, if that's what he meant.

    Thing is, I am not feeling I'm going to be able to solder much more. I had a hard time soldering today, my hands were shaking. I might possibly be having some nerve problems to be honest. :/
     
  19. Barone

    Barone Active Member

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    I think I just missed this post previously...
    I would like to ask you and/or APE about Sega CD games and overclocking...

    I've read many times that overclock will always break the Sega CD compatibility and the system will really freeze when you try to boot it up with the Genesis overclocked (my tests also supported such info).
    However, I have a theory (I haven't had much time lately to test it) that Sega CD games which run totally on the Genesis CPU, like Sonic CD, should work if you halt the Genesis CPU and change the clock during the game. According to my experience, anytime that the Genesis communicate with the Sega CD while the first is overclocked, it WILL freeze. So, I would like to know how you managed to play the game overclocked and if it freezes when it has to load the next stage or something. I also doubt that it will work during the past stages 'cause the Sega CD uses its own soundchip to produce the music there and I think there's constant communication between both systems during the that... But I might be totally wrong. It can also be only playable using a X'Eye/WonderMega too, IDK...
    Any extra info in this subject would be pure gold, really.
    Some other Sega CD games which run on the Genesis CPU: Sol Feace, Flashback (of course not during the FMV playback parts), Lords of Thunder... Well, there are many other but I'm kinda out of memory now.



    Cool! Congrats!


    Gotcha.
    Yeah, probably not a good idea to deal with your Sega PAC, I would be really afraid of fucking it up.




    AFAIK any Sega CD model, combo or not, will fail to boot with the Genesis/MD CPU overclocked. In my tests, it also freezes during any communication between both sides, even in cases like when Pier Solar tries to boot the Sega CD if you have it attached but with no CD inside.


    More related info here: http://gendev.spritesmind.net/forum/viewtopic.php?p=8728


    Maybe too much coffee? It usually freaks me out and makes my hands shake a lot.
     
    Last edited: Dec 30, 2012
  20. lnx64

    lnx64 Robust Member

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    Haven't had coffee. I've been suffering this for a while in my left hand. My right hand is fine but I'm a lefty.

    Ps my 32x won't even allow genesis games to start when in 10mhz. And if it does its always randomly tapping the down arrow automatically.
     

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