Need explanation of the CPU and FPU technology on turbo boards

[kidkoala]

@piru, shoggoth

another problem could be cooling? if his fpu gets to hot it could possibly create bad data?

another thing: why does the cd32 have so many oscillators?
the one that's used for the 14mhz cpu i guess is the 28mhz oscillator (running at half speed)? and there's a 16,9mhz osc. around the area of all the video output, that's because video runs at 32fps and that the double of 16mhz?

wouldn't it be possible to overclock the cpu osc. or something then?

just asking..

[kidkoala]

hehe maybe an unrelevant example, but that guy who had been overclocking since 1975, that 1975 overclocking was his calculator, and when doubling the the clockspeed the calculator worked as usual but it calculated wrong answers

also, if you want the best of the best 68030 cpu, for overclocking-purposes (or whatever) you can order brand new 68030/50C from Rochester Electronics (i've just been mailing with the,), at the humble price of 144$ a piece, produced in 2002

[rkauer]

FPU built in 68030? The full 030 have a MMU, not a FPU!

[kidkoala]

who and when in th thread are you reffering to?

[Hyperspeed]

Hmmm, so a 68030RC50C could be overclocked quite stable? Is it possible I wonder to have a 64Mhz SX32?

:inquisitive:

[kidkoala]

"I have also found over the years that more recently made versions of a particular chip will often overclock to a higher frequency. For example you would be more likely to get better results from a 4 year old 68030 compared to one that is 7 years old. Likewise you will usually get less from a chip at the top of it's range compared to a lesser rated one. For example you will usually be able to overclock a 25MHz 68030 further than a 50MHz 68030.

Thirdly you need to bear in mind that the accelerator card itself will also limit maximum possible overclocking speeds. A good example is the Commodore A2630 which cannot be clocked past 29MHz - even if you install a 50MHz 68030 in it."
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Quoting this _very_ experienced overclocker, I think that a
4 year old 68030/50 will overclock better than a 10-15 year old one, for more than one reason (better design, better materials, not old rotting electronics;).
But he also says that a top o' the line cpu will clock less than a smaller one, so I guess someone just has to try this out..
The Viper and similar accelerators were often sold overclocked, hence the problems with heat (in addition to generally bad design in some of them), I guess the 50Mhz were overclocked 42mhz or something..

Thirdly, like he says, is that the internal architecture of accelerators and motherboards often set a limit to the highest clockspeed a cpu can have, like he mentions the A2630 wich cannot be clocked to more than 29Mhz even if the 030 is 50Mhz..

A question then rises: What are the limits of eg. the CD32, the A1200, and the A600?

[DamageX]

The trouble with an A500/600/1200/CD32 is that there is interleaved memory access between the CPU and chipset (unlike a PC or a Genesis) so I guess if they are running at different speeds the clock signals still have to "line up" at certain times. On Aminet there are some tales of hacking an A500 to run at 14MHz (2x the chip bus), maybe an A1200 could run at 21.5MHz (3x) or something?

As for the A2630, I think Dave Haynie's archives had some updated PALs that helped with overclocking if the card had 80ns or faster RAM on it.

One time my brother and I each had the same model x86 motherboard, and 400MHz Celerons. His would run at 600MHz but mine wouldn't boot at that speed, I could only get 570MHz. It just depends on the chip. Later I got a 500MHz chip for cheap and that one wouldn't go past 575MHz! And of course this was already past the good ol' days where you could change the multiplier, so the 500 was slower than the overclocked 400 because of bus speed.

[shoggoth]

DamageX wrote:
The trouble with an A500/600/1200/CD32 is that there is interleaved memory access between the CPU and chipset (unlike a PC or a Genesis) so I guess if they are running at different speeds the clock signals still have to "line up" at certain times.

Same thing on the Falcon. The solution there is to use some extra logic which switches between 32 & 16Mhz, causing it to run in 32Mhz when not accessing the bus (typically speeding up  stuff which resides in the cache and slow instructions). As soon as it access the bus, the clock is switched back to 16Mhz. Afaik both clocks must be in phase, or it won't work.

I think the same approach is used to overclock A500:s, and possible A1200:s. I may be wrong though.

Another approach on the falcon is to speed up the entire bus+cpu to 25Mhz, simply by replacing an oscillator on the mainboard. Don't know if that can be done on the Amiga without screwing up the refresh frequencies etc. for the screen? If possible, it should give a lot better performance compared to just double-clocking the CPU as I described earlier.. Well, I guess it's fairly obvious that I'm not too familiar with all aspects of Amiga hardware.. yet..

-- Peter

[Piru]

Overclocking the motherboard clock is out of the question as it will skew all chipset timing.

[shoggoth]

Piru wrote:
Overclocking the motherboard clock is out of the question as it will skew all chipset timing.

If all clocks in the system are derived from the same master clock, and you replace that master clock with something higher, I can see no reason why it shouldn't work - provided that one keeps it within a sane range.

However, since it would most probably screw up screen synchronization, baudrates, sample rates and other I/O, yeah, it's probably not a good idea... forget what I said.

-- Peter