Overclocking the Dreamcast.

[ptr.exe]

Okay i finally understand fully how to overclock the DC, but have now hit another snag, finding a 40mhz crystal in a shop is impossible, maplin used to do them but have stopped selling them, so anyone know of a place that stocks them in the UK?

[FrierTuck]

wait, why do people need to over clock the dc, i dont get it

[mh777]

Some games run better with the DC overclocked (i.e. no Shenmue 2 slowdowns), as well some emulators, from what I understand.

[Kamjin]

Also, just for the fun it, kinda like putting neons on your pc, and making your grass greener than the neighbours..
Although it still has one major drawback, the clocks are messed up so you can't save properly. Still.. that could probably be worked out by adding some logic to safely "stretch" the clk back to the original source when maple access's are happening.

[ptr.exe]

Kamjin, I had a feeling you would reply to this post as in most threads about overclocking your name usually pops up
I didnt know you couldn't save, wouldnt it be possible to modify a VMU to read and save at the same clock as the DC? would be messy and probably very unreliable, and i have very little knowledge on this topic so probably not.

Anyway ive found a place that does the crystals www.kellnerinone.co.uk

[Kamjin]

I enjoy hacking the dreamcast!

The vmu corruption doesn't seem to always happen, but it does most of the time. I never found the exact cause of it. the weird part is.. based on the way the vmu works.. it shouldn't happen. From the VMU side there's not much you can do. But you can at least make a switch that let you turn off the dreamcast, and change the clock rate (I'll type out how below).
You could try different crystal speeds to see if something a little slower will actually let you save reliably.

When you go to build it, you'll want to make a switch that let's you select the clock rate. You can do this by simply lifting the clk pin rather than cutting it (I remeber seeing a tutorial that said to cut it).
What you do is use something like a dentist pick, or a very fine flathead (like one from a jewel/glasses kit)
Put the pick just under the pin where it connects to the chip, and use the pin beside it as leverage. then you put the soldering iron on the pin, and lightly put pressure to lift the pin with the pick, not to much, you dont want to lift the pcb trace with the leg. Once you got it up a couple of millimeters, take a look under the lifted pin, to make sure that there's no solder still connecting it to the pin. if there is you can heat it up a lift it a tad more, or use copper wick to suck the remaining solder.
Then slowly lift the pin up to give yourself enough room to solder a wire onto the pad where the pin was, solder another wire on the pin.
Get a 2 poisition 3 contact switch solder the centre contact to the wire that is soldered to the pad.
solder one of the end contacts to the 40Mhz xtal wire.
solder the other end contact to the 33Mhz wire you soldered to the pin.
Now you have a speed select switch.

You can't switch it live, since the dreamcast will hang about 50% of the time when you try. But you will be able to use it normally when you want.

[ptr.exe]

Thanks, i planned on having a switch anyway as i knew there were certain games the wouldnt run on an oveclocked DC, when you say 40Mhz xtal wire you mean the wire that carries the 40mhz clock signal from the crystal oscillator, right?

Does it matter that the wire from the 33/40Mhz pulse signal is long? (25cm there and back) as ive heard the signal won't carry well over a long wire.

When you say it doesnt save most of the time, do you mean if it wont save if i keep trying it might eventually work or does it depend on the game?

I was also going to ask you is there anyway of switching 33/40 with the DC on, but youve already answered that Q. so thanks

[Kamjin]

Thanks, i planned on having a switch anyway as i knew there were certain games the wouldnt run on an oveclocked DC, when you say 40Mhz xtal wire you mean the wire that carries the 40mhz clock signal from the crystal oscillator, right?

Yup, 40Mhz from the output of the xtal to one of the outer legs of the switch
33Mhz from the chip pin you lifter to the other outer leg
and the middle leg of the switch to the PCB pad to feed the clock to the cpu.

Does it matter that the wire from the 33/40Mhz pulse signal is long? (25cm there and back) as ive heard the signal won't carry well over a long wire.

It's very important to keep them as short as possible at these speeds,
just give it enough to reach the edge of the case where you're going to put the switch, don't tape or twist the wires together. Keep them loose and slightly away from each other.

When you say it doesnt save most of the time, do you mean if it wont save if i keep trying it might eventually work or does it depend on the game?

I was also going to ask you is there anyway of switching 33/40 with the DC on, but youve already answered that Q. so thanks

It's pretty much random, problem is that if the game doesn't let you see the saves then you don't know if it went fine, and it also seems to corrupt the the entire vmu (needing to format it again).
I've already got an overlocked dreamcast in pieces on my workbench, on summer break I was planning grab a shovel and clean my workbench and to try upping the freq in steps to see the effect. I'll also try to see if I can build something simple (using cmos or ttl) that would let it switch clks live, that would be a way to get around the problem.

[qatmix]

Indeed, I have found that I have a 3rd party Memory card which doesnt corrupt at all. I was always careful about corruptign a save, but whilst tryign Rez the autosave came on and corrupted my memory card so I still need to try to hex edit my PSO char so it will work again (200 hours lost )

as to the wires, Obviously if you use thicker wire its not so much of a problem, but its best to keep it as short as possible.

Im also overclockign the GPU, Im trying to overclock the GPU and the CPU by the same ratio to see if that resolves the VMU issue. Its jsut a case of findign the correct crystals.

[ptr.exe]

Qatmix, so your 3rd party mem. card can save when your DC is OC'd? or it just doesnt corrupt? lucky in either case, ive had so many 3rd party cards that corrupted so easily.

I thought thicker wires would be worse, as basic physics says there are more fixed and 'free' electrons in the lattice but some of the 'free' electrons will transfer no energy so all you're really doing is increasing the number of fixed electrons causing obstruction and therefore increasing resistance. I may be wrong but im pretty sure thats correct.

What are you overclocking the GPU to? if your increasing CPU by 7Mhz (17.5%) then you'd be increasing GPU by 9.5Mhz to 63.5Mhz that seems too large perhaps you should start lower but good luck anyway, if i had the knowledge then i'd have a go but i'd probably end up frying the DC