Ok so tonight I had a bit of fun Overclocking my early NTSC 837-6067 model 1 Sega Master system. Nothing exceptional here, just a good old fashioned crystal oscillator switch overclock. Pretty much the same exact procedure that is routinely used on the Genesis. Still, overclocking a SMS seems to be less popular than overclocking the Genny so it is less documented on the Net. Let me tell you about my personal experience with it. I unsoldered and lifted the clock input pin ( pin 6 ) of the Z80. Connected wires to both the pin and the cleared solder hole where it used to be. ( the orange wire is grabing +5v on a nearby pad ) This is connected to a small protoboard with a socket for the new crystal. I made it so I can easily swap the oscillators for new ones and I used a DIP 16 socket so it is compatible with both half size and full size oscillators. Then added a small switch to choose between stock speed and the new oscillator. Pretty straightforward test setup. I had purchased 2 oscillators. One is 4mhz and the other is 4.9152 mhz. I tried 4 games with both oscillators. Basically, in all my SMS games there are only two that I know to have slowdowns. R-type and Power Strike ( aleste ). I also tried with WonderBoy3 and Rastan. They are all games that use FM sound, I was curious to know if there would be some problems when using an overclocked SMS along Tim's FM expansion board. I was also curious to see if this would influence WBIII choppy 30fps scrolling (Spoiler: It didnt... ) Anyway, here is what I observed. Power Strike/Aleste -4mhz: Small visual glitch in the SEGA bios screen. Moderate graphical corruption in the intro screen of the game. Glitch free gameplay and less slowdowns. -4.9152mhz Heavy graphical corruption on the Intro screen ( see picture ) . But actually no corruption at all during gameplay. I observed no glitch, and absolutely no slowdowns. This game has regular slowdowns at stock speed and even at 4mhz but at 4.9 there are none and it plays great. Its actually pretty crazy when the screen gets filled with crap and all the bullets come at you full speed. I played through a few levels at this speed and the game ran perfectly ( for the exception of the intro screen ) WBIII -4mhz: Small visual glitch in the SEGA bios screen. No other effects. -4.9152mhz Occasional minor sprite corruption, no other effects. R-Type -4mhz: Small visual glitch in the SEGA bios screen. Glitch free gameplay and less slowdowns. -4.9152mhz Sprite corruption during gameplay, FM Music getting somewhat out of sync. No slowdowns. Rastan -4mhz: Small visual glitch in the SEGA bios screen. No other effects. -4.9152mhz No effect at all. General observations: -To me the most interesting thing is that all games have some random graphical corruption during the SEGA bios logo at 4mhz. I was expecting it to go batshit when I used the 4.9 mhz crystal but no... The SEGA logo is just fine with that crystal. ( I am stumped ) -The Z80 on the SMS is rated for 4 mhz, so it is underclocked at stock speed ( 3.5xxx mhz ) . When overclocked, even up to 4.9 mhz, it keeps cool and stable. My guess is that this chip does not give a shit about being 25% over its rated speed. The glitching that was observed likely originates from timing issues on a system level. And not from the processor. - The FM board seems compatible with overclocking, with the exception of R-type at 4.9mhz, but issues were still mild. - I am not aware of any game on the SMS that have more slowdowns than Aleste, if you do plz tell me. And with the 4.9mhz overclock, the slowdows are completely gone. What this tells me is that it would be useless to even try to go any higher than that. Even 4.9mhz is probably needlessly high. - I should have bought more crystals!!!! D: Yeah somehow I really wonder why I did not buy a 4.5 mhz or something crystal. PAL SMS users can actually use the clock of the video encoder to overclock the CPU to 4.4xxx mhz but that would not work for NTSC users as the NTSC encoder uses the stock speed. We need to buy crystals. - I will probably try to get more crystals in the Future to find the sweet spot speed. - Some of you possibly saw this coming, I want to try this on the Game Gear next
I remember slowdown in Sonic 2, not exactly where. Maybe in the first stage while breaking the spikes with the mining car. In Tom and Jerry you can see some slowdowns in all the stages as far as I remember. I've mastered this game so much that I've played just with the running and jump buttons and the long and short steps just for "perfection" lol. I love Tom and Jerry. In Submarine Attack, I remember playing with the Submarine very near the right screen edge, because I wanted a "flawless" gameplay. The shooting is really fast when the shots leave the screen fast. Maybe you can achieve faster shots in the whole screen. I think that you can see some slowdonws in Scramble Spirits. If the two players use two bombs each, surely you'll see slowdown, but that's not a nice way to play. You can use one bomb at a time because it clears the enemy fire. So it's not wise to waste them. Well, Scramble Spirits is a damn nice game.
Some other games with heavy slowdowns are apparently Sonic Chaos and Dynamite Dux, among others. Im pretty confident that you can get all SMS games to run without slowdown with overclocking. The problem is getting them to run glitch free. Tiido told me that it actually works better if you overclock the Z80 in a genesis and use the powerbase converter. Here's what he said. If I do more experiments I will post here.
Wow! Nice work! I'd be most curious to see how a Game Gear goes. I've still got a few I have in pieces somewhere around here! Although I wouldn't mind bumping my Power Base Converter up a few notches! :smile-new:
That's what my guess would have been. In old systems like that, all the components are quite "close". Not just physically close on the PCB, but logically too. Overclocking the M68k on Mega Drive and NeoGeo is less glitch prone, because things are a bit more abstracted from one another. (E.g. the Mega Drive's FIFO buffer mentioned by Tiido) Heck, if you HALT the CPU in a Mega Drive, the music keeps playing!
I tried hot switching the clock on the SMS. With pause or without pause. In both cases the console froze. I would have already tried it on the game gear but I am cautious as my game gear board is currently so crammed with mods and work hours that I do not feel like subjecting it to untested experiments. I wish I had a second game gear to do the test. I do not know if some GG games have slowdowns, overclocking it might be more oriented with the Idea of playing SMS games on it. Also, since the GG is more integrated than the SMS, I expect it to behave differently than the SMS. Possibly better. I only found one mention of it being tried on a GG and apparently it worked pretty well. Not much details though...
Not surprising, the switch needs to be debounced and you need an arbitration circuit so that neither clock phase is cut too short during the hand off.
ram upgrade may help i do not know much about sms and/or genesis hardware amateur radio transceivers are a different story for me ram upgrade in my kantronics kpc3+ tnc for digital mode aka packet radio fixed a few issues.. with data corruption im just glad i found a good welder butane soldering iron that converts into a smd iron... gets about 2 hours of run time when filled to max capacity got a good adjustable flow valve that gives awesome heat con troll i made a ground strap for the iron too$13.50 at my local MicroCenter Xeveniah/KG4QGK
