Centris 610 @ 40Mhz possible?

[Vahan]

Hi all,

In my quest to squeeze the most from my Centris 610, I'm trying to get it to run the upgraded 68040RC40 02E31F at its full 40Mhz speeds.
I've upgraded the clock driver from XC88916DW55 to MC8891DW80, but I haven't been able to make the computer chime with a 20Mhz SG-615 clock so far.

It chimes initially but then plays the sad tones with 16Mhz and 16.384Mhz clocks, and the maximum clock that works with the system stable is 14.318Mhz.

Am I missing something, or did I just get unlucky with a dud 68040 CPU (I got it from ericwoosrarechips)?

 

[Byrd]

It's not so much the CPU but the rest of the architecture serial/SCSI/video/RAM and VRAM speeds that are marginal at higher clock speeds. Upgrading the clock driver doesn't really help in this instance. Most Centris' 610 get to 28 - 29Mhz at best.

 

[Vahan]

Thanks for confirming my fears, but I have seen several posts and YouTube videos of people achieving 40Mhz. How is that possible?

 

[cheesestraws]

Because the speeds that the parts are guaranteed to operate at and the speeds that they can be pushed to operate at are two different things, and the latter is far, far less consistent. When you get, for example, an 040 that is rated at 25MHz, all that means is that it is guaranteed to operate at 25MHz, and was sold to operate at that speed. It might actually be capable of running at 40; it might not; it might result in a ritual curse being put on your family if you try it. There are no guarantees. The same is true for every other part in the machine: they are guaranteed and tested to work at a specific performance level, and anything higher is an inconsistent bonus that depends upon the individual parts, the phase of the moon, how polite you've been to your cat, etc. etc.

What this means is that just because someone else on the Internet managed to get their Quadra to 40MHz doesn't mean that yours will go to 40MHz. And actually it doesn't mean that theirs will be at 40MHz reliably - maybe it only works well enough to get to the speedometer display, and maybe they're just not going to mention that because people on the Internet mostly want to look good (selfie syndrome but with computers, right?).

As soon as you depart from what the parts are specified to run at, you are in a world where, in theory, anything could happen - realistically it will be 'work' or 'not work' or the grey area between them - and you can't necessarily take individual other people's experiences to represent what will happen. You would need a large statistical sample, including the failures, to know.

 

[cy384]

If you get faster RAM you might have better luck. Converting it to report as a Quadra 610 might give you some headroom. Some ROM hacks might be needed to go faster as well. Depends on what exactly the limiting factor is, and you might be out of luck anyway.

 

[joshc]

The 650 lends itself a lot better to this sort of thing, so worth trying to get one of those.

That said, higher speeds have been done on a 610 before - so it's not impossible, it's just harder.

You may find this page useful

C610 Ethernet Modification

 

[Vahan]

If you get faster RAM you might have better luck. Converting it to report as a Quadra 610 might give you some headroom. Some ROM hacks might be needed to go faster as well. Depends on what exactly the limiting factor is, and you might be out of luck anyway.

This is the next thing I'm going to attempt. As stated on http://www.applefool.com/clockchipping/610.html, there is resistor R137 apparently responsible for the gestalt ID (52 vs 53), perhaps having the board identify itself as a Quadra might unlock some timings somewhere.

 

[Vahan]

If you get faster RAM you might have better luck. Converting it to report as a Quadra 610 might give you some headroom. Some ROM hacks might be needed to go faster as well. Depends on what exactly the limiting factor is, and you might be out of luck anyway.

Yet another thing to test. I'm currently using 2x32mb EDO RAM sticks. Perhaps I need to re-test with them removed and only onboard RAM available. I've also maxed out the VRAM. I've also done the Ethernet clock decoupling, but my tests have shown that Ethernet availability is not tested during the power-on and is not a cause for the sad tones or no chime at 16mhz+ clock speeds.

 

[Vahan]

My initial inspiration was Phipli's short video, which looks legit.