Overclocking a Sega Saturn?

[nukpana]

A few years ago, I bought a Model 2 European Sega Saturn (MK-80200A-50) from eBay mainly for nostalgic reasons. I had a saturn when it first came out, and since I was not in a position of any finance back then, I wasn't able to get all the games I wanted. However, since my aquisition of my new Saturn, I have been able to get some of the games which I wasn't able to get back then.

My falvorite of these games is Shining: The holy ark, however I have noticed that in certain places the game slows down to what is almost a halt. I sometimes get slight skips and lag when playing other high memory load games (for a saturn) such as Exhumed, thought these arn't as bad.

I'm an enthusiastic modder, though I've not done anything too brilliant as of yet, just made my own AV cable for my saturn, added a few LEDs to my DC, resurected my saturn from the logo crash, minor things. Now I want to try and overclock my saturn, and try to get better performance from it.

I was wondering if anyone has ever tried this before and whether, if they have, they got better visual performance or even faster load times?

I'd like to ask, if anyone has any information on how to proceed, could you please help me?

I have found the original pinouts and documentation for the SuperH-2 (SH-2) 7604 and SH-1 (7032) on google, and by using them I have been able to locate the clock pins, both input and output, but I'm not sure about what to do with them. From what I've read, I think I'm supposed to feed them a faster clock signal, but I'm not sure how to do that. Either that or boost the voltage.

Any help would be deeply appreciated!

Thanks!

-Nukpana

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Links are as follows

SH-2 7604 Product Overview http://www.classicgaming.com/epr/saturn/h12d0.pdf

SH-1 7032 Overview http://www.rockbox.org/twiki/pub/Main/Data.../cpu_sh1_pb.pdf

SH-1 7032 H/W Manual. http://www.rockbox.org/twiki/pub/Main/DataSheets/sh7032h.pdf

 

[cgfm2]

I was wondering if anyone has ever tried this before and whether, if they have, they got better visual performance or even faster load times?

There are a couple of problems with the Saturn that make overclocking difficult:

The video hardware uses the same clock as the CPUs. In fact when you select the 26 or 28 MHz operating speed for the SH-2's, the video chips run at a different speed accordingly and games have to use different display modes. If the CPUs were overclocked, the video hardware would run too fast and it wouldn't generate NTSC/PAL compatible video anymore.

Assuming you fed the video section the 'old' clock and just boosted the CPU clock, this means that both SH-2s *and* the SCU would need to run faster, as the SCU manages all memory access for both chips. The SCU coordinates access between two buses (A and B) which may need to run at the same speed; the video hardware is on the B bus so there's another potential problem if the video clock differs from the CPU/SCU clock.

I think the sound system is clocked separately, but if not then you'll have music pitch problems for games that don't use CD-DA audio.

CD loading would probably not be faster; the main limitation is how quickly the CD-ROM drive can read data off the disc and present it to the CD subsystem, which from there is queried by the main CPUs for data. Assuming the SH-1 was overclocked, it would still spend the same amount of time polling the CD hardware for data and likewise for the SH-2's polling the SH-1 for data. No speed gain there.

Finally a limiting factor is how quickly the VDP1 can draw polygons. Games can tell if it's finished drawing a display list or not, and if it takes too long they can wait (slowdown) or abort rendering to regulate speed. If anything you might get a speed-up from overclocking the VDP1 only, though it has pretty tight memory timings and you may get corruption problems. Also there's a chance the VDP1 has to be in sync with the VDP2 (it scans out data to VDP2 at the same rate as the display is scanned, I think) meaning an overclocked VDP1 would result in serious distortion to the polygon layer.

The short answer is: the Saturn is such a complex and interlocked mess that it's impossible to tweak one part without disturbing the other parts.

 

[nukpana]

Originally posted by cgfm2@Thu, 2006-04-20 @ 07:59 PM

The short answer is: the Saturn is such a complex and interlocked mess that it's impossible to tweak one part without disturbing the other parts.

[post=145808]Quoted post[/post]​

Agh! Well, I suppose that throws my plan out the window. Thank you though I'll keep thinking about alternatives. But from the sounds of it, its too complex for the likes of me.

What about swapping th RAM chips for slightly better ones? I don't think that would make much difference though, since games on the saturn are designed around its limited memory

 

[cgfm2]

Originally posted by nukpana@Thu, 2006-04-20 @ 02:31 PM

Agh! Well, I suppose that throws my plan out the window. Thank you though I'll keep thinking about alternatives. But from the sounds of it, its too complex for the likes of me.

What about swapping th RAM chips for slightly better ones? I don't think that would make much difference though, since games on the saturn are designed around its limited memory

[post=145809]Quoted post[/post]​

I think the only way to make use of faster memory would be an overclock.

IIRC the SH-2 or SCU has controls to set memory wait states, which the BIOS initializes and games aren't supposed to touch. If you swapped out the SDRAM and DRAM with faster equivalents, and patched the BIOS, or the game, or made a PAR code to set the reduced wait state values, you may get a speed-up.

It would probably be a good idea to find out what the default values are and if there is much room to reduce them; assuming the fastest settings aren't used by default. I wonder if one of the Saturn emulators can log values written to the SH-2 BSC or SCU registers to find this out. (AFAIK settings for SH-2 #2 would be the same as #1)

 

[RockinB]

Yes, the sound block got it's own clock.

Good idea with the VDP1 only overclocking! The VDP1 framebuffer is the only thing accessed by VDP2. If it is split into two physically different banks, then it could be possible to switch their clock when switching framebuffers.

I thought about replacing memory, too. It would be great(!) to have faster and/or more low workRAM (or whatever RAM area, the VDP2 is explicitly able to handle twice as much as in Saturn). BTW: the low RAM is slow AS HELL

 

[nukpana]

Originally posted by Rockin'-B@Thu, 2006-04-20 @ 10:35 PM

I thought about replacing memory, too. It would be great(!) to have faster and/or more low workRAM (or whatever RAM area, the VDP2 is explicitly able to handle twice as much as in Saturn). BTW: the low RAM is slow AS HELL

[post=145812]Quoted post[/post]​

I know what you mean, but I've measured up the ramchips on the base of the saturn motherboard against normal pc100 chips, they look to be one or two pins too big for them. I'm not sure how fast the saturn ram runs, but I doubt its pc100 anyway. But From what I can recall, it uses SRAM not SDRAM.

The question is, where could we find SRAM that is faster/larger and that would be compatible with the saturn?

As for the VDP1 and VDP2, I need to do more reading up on this I'm not a complete newbie, but you've lost me there!

 

[cgfm2]

I know what you mean, but I've measured up the ramchips on the base of the saturn motherboard against normal pc100 chips, they look to be one or two pins too big for them. I'm not sure how fast the saturn ram runs, but I doubt its pc100 anyway. But From what I can recall, it uses SRAM not SDRAM.

Err.. what you'd want to do is write down the part numbers, find if the manufacturer still makes them in the speed grade you want, and optionally look up equivalent parts in a memory cross reference list if the part is out of production. Then assuming you've found a good candidate for a replacement part, find out who sells 'em; in the US using www.findchips.com is a convenient way to search the inventory of multiple companies.

In case you don't want to open your Saturn here are links to schematic diagrams of the various memories it uses. I think the author has mixed up some of the RAM functions, so don't take it at face value - this is more useful for the part numbers and pinouts than anything else. They also list alternative part numbers.

http://www.geocities.co.jp/SiliconValley-S...268/052r3l0.htm

http://www.geocities.co.jp/SiliconValley-S...268/052r3l5.htm

http://www.geocities.co.jp/SiliconValley-S...268/052r1l7.htm

http://www.geocities.co.jp/SiliconValley-S...268/052r1l6.htm

The other factor besides the VDP1 VRAM used for texture map data and the display list, are the two framebuffers. I am guessing those are two 256Kx8 SRAMs but don't actually know. If you were going to overclock the VDP1 then both it's VRAM and the frambuffer RAMs would need faster parts.