Overclocking GVP Combo 040

[abraXXious]

Hey guys.

Now that I have this running rock solid stable (weird gfx corruption and instability problem was caused by icons being stored in Other Memory instead of Chip), I would like to overclock it!

Not by much mind, it is currently running at 33mhz, I would like to knock that up to 40. Now I already have some 40mhz 68040s (XC68040RC40M), so even though a modest overclock from 33 to 40 would probably be quite stable with the old 33mhz, I thought I may as well replace it with a faster part to be safe.

The Combo 040 has a socketed cpu, so just a quick swap there. And the clock crystal is also socketted, so can anyone see any problems with swapping the cpu and clock crystal to knock it up to 40 mhz?

 

[rkauer]

Search for a MC68040 part: they don't heat much and are better on faster clocks.

 

[abraXXious]

Hey there,

yessum, the MC series is always preferred, but if I only go to 40 mhz, surely heat wont be a big problem - since that is what the XC is rated for (40 mhz)?

 

[rkauer]

I have an Apollo 1240/40 (too bad it have the 130 MACH chips...), it does not heat insanely as it's other slower brothers.

I think it is because Motorola tested the CPU one-by-one and labelled them accordingly to the clock they can work for an intense burn-in-test.

More: I think the "burn-in-test" concept was created by Motorola because this very CPU, LOL.

 

[abraXXious]

Okiez, I have now replaced the XC68030RC33E (whats the E stand for?) with an XC68040RC40M (erm, and the M - what does it stand for???), glued on a heatsink with some nice artic silver....

....and it boots and runs still (I never doubted it for a minute)! Of course, it is still only running at 33 mhz atm, but Im letting it "burn in" the heat transfer compound by endlessly running a doom II demo via Adoom (give the cpu a good work out).

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

I suspect it will run flawlessly, and I can probably kick it up to about 46 mhz. The GVP Combo 040 came in three flavours - 25mhz, 33mhz and 40mhz, and from I can see, the only difference between them was the cpu and clock crystal. All other hardware, controller chips etc are identical, so if the 40mhz version of the board can run at 40 mhz with a 40 mhz 040 installed.... by replacing the 33mhz 040 on this 33mhz board with a 40 mhz 040 and matching crystal, I have essentially turned this GVP Combo 040 33mhz version into the 40 mhz version - until I go OVER 40 mhz I am not really overclocking anything.

Anywho, will be interesting to see if it will go up to say 46 mhz (I believe if you go much over this that the controller/logic chips will start to malfunction and cause stability problems long before the cpu does).

 

[LTAC]

XC= not a fully qualified part / Engineering sample / Pilot production device
RC= Ceramic PGA, gold lead finish
E or M = Processor revision

 

[abraXXious]

Thanks LTac - tell me, which is the best revision out of E and M?

 

[rkauer]

M are from MC parts only.

 

[LTAC]

Read this:
http://eab.abime.net/showpost.php?p=745447&postcount=7
http://eab.abime.net/showthread.php?t=51276

 

[matt020]

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

 

[AndyLandy]

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

Maybe he wants to under-clock the '040 to 10MHz?

 

[cosmicfrog]

replaced the XC68030RC33E (whats the E stand for?) with an XC68040RC40M

and that did`t confuse you at all then hehehehehhehe, If only such a thing was posable

oh and Dam my 040 is`t socketed so I can`t replace that and niether is my crystal

Think hes got the right size(Mhz) crystal as my is 16.50000000Mhz and think she runs at 33

 

[abraXXious]

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

Maybe he wants to under-clock the '040 to 10MHz?

Noperz Andy mate, the GVP card is something of an enigma.... wrapped in a mystery... then plastered to a PCB....

Erm, what was I saying? Oh yes. The GVP Combo 040 actually DOUBLES the 040 clock (instead of halving it) so a 20 mhz clock will drive the onboard 040 at 40 mhz. The original clock was 16.5 mhz..... which of course gives the 33 mhz.

Got it?

---------- Post added at 05:39 ---------- Previous post was at 05:38 ----------

Hey Matt020 - see my last post.

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

 

[psodas]

@AbraXXious
First of all a crystall at 10Mhz will result the operation of cpu at 20Mhz! The crystall frequency in this board doubled to meet the needs of each cpu. So for 040/25 or 33 or 40 You need respectivelly crystalls at 12.5 or 16.5 or 20 Mhz. That is a fact!
After how will you change the proccessor? As I know this accel card has on board direct solder the cpu. Unless you have some special version of this 040 combo!
In other way you must desolder the cpu and place a socket first! But you must also find a very very low profile heatsink and fan or the same -if work- who shipped from the manufacturer. In other case heatsink-fan combo it touches on the metal of floppys holder!!!!
I sugest to be carefull with this retro material! Is very expensive, very hard to find, and believe me some out there would like to have one at any speed! Even at 25Mhz!

 

[SpeedGeek]

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

The 040 does not halve any clock. The 040 requires 2 separate clocks BCLK and PCLK. PCLK is 2x the frequency of BCLK. Motorola rates the 040 according to BCLK and accelerator designers choose clock dividers or clock doublers to generate one of the clocks.

 

[AndyLandy]

Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.

The 040 does not halve any clock. The 040 requires 2 separate clocks BCLK and PCLK. PCLK is 2x the frequency of BCLK. Motorola rates the 040 according to BCLK and accelerator designers choose clock dividers or clock doublers to generate one of the clocks.

Ahh, that all makes sense. Finally an answer to the '040 weirdness question. Nice one, SpeedGeek. I assume this is not the case with the '060?

However, that doesn't explain why you'd ever build a CPU card with an oscillator that's half the rated clockspeed. If you're running an '040/40, surely that'll be a BCLK of 40MHz and a PCLK of 80MHz. So either use an 80MHz Xtal and 1/2 it for BCLK or use a 40MHz one and double it for PCLK.

If you have a 20MHz Xtal, surely you'll need to double it twice to generate the PCLK?

 

[abraXXious]

first of all.... what are you talking about?!? I KNOW the Combo card doubles the clock frequency for the 040 - that is why Ive ordered a TWENTY Mhz crystal - Andy is the one who mentioned 10 mhz clocks!

... if you read my previous post you will see I even say the combo card is a strange beast that uses a half speed clock crystal to clock the 040 - that is a fact!

I have ALREADY changed the cpu! - Combo 040s have the cpu in a socket, NOT soldered to the board.

Desolder?! Good god boy what ARE you talking about?!?!

I alreadh have a low profile heatsink and fan fitted, misses the hard disk/floppy mount cradle by about 3 mm.

As for being expensive - I know, I have dozens of miggies and my wife moans every time I buy another one.

@AbraXXious
First of all a crystall at 10Mhz will result the operation of cpu at 20Mhz! The crystall frequency in this board doubled to meet the needs of each cpu. So for 040/25 or 33 or 40 You need respectivelly crystalls at 12.5 or 16.5 or 20 Mhz. That is a fact!
After how will you change the proccessor? As I know this accel card has on board direct solder the cpu. Unless you have some special version of this 040 combo!
In other way you must desolder the cpu and place a socket first! But you must also find a very very low profile heatsink and fan or the same -if work- who shipped from the manufacturer. In other case heatsink-fan combo it touches on the metal of floppys holder!!!!
I sugest to be carefull with this retro material! Is very expensive, very hard to find, and believe me some out there would like to have one at any speed! Even at 25Mhz!

 

[AndyLandy]

first of all.... what are you talking about?!? I KNOW the Combo card doubles the clock frequency for the 040 - that is why Ive ordered a TWENTY Mhz crystal - Andy is the one who mentioned 10 mhz clocks!

... if you read my previous post you will see I even say the combo card is a strange beast that uses a half speed clock crystal to clock the 040 - that is a fact!

I have ALREADY changed the cpu! - Combo 040s have the cpu in a socket, NOT soldered to the board.

Desolder?! Good god boy what ARE you talking about?!?!

I alreadh have a low profile heatsink and fan fitted, misses the hard disk/floppy mount cradle by about 3 mm.

As for being expensive - I know, I have dozens of miggies and my wife moans every time I buy another one.

Woah! Calm down, boy! Nobody mentioned a 10MHz Xtal, only posited that if you use a 20MHz Xtal on most '040 cards, you'd be clocking the CPU at 10MHz.

I'm sure you're right about what Xtal your card needs, but it still strikes me as barmy. The '040 needs two clock signals, one at the rated speed, the other at twice that. If you use one that's half the rated speed, you need to double it for the rated speed, then double it again for the other clock signal. What were GVP thinking? Unless they have a bunch of half-speed logic on the card, it seems excessive to have to provide multiple multipliers (although I don't imagine they're expensive)

 

[abraXXious]

Lol, I was taking the p|ss Andy!

psodas just got his wires crossed, so I thought I'd take the opportunity to do a little hand slapping.

---------- Post added at 20:17 ---------- Previous post was at 20:16 ----------

Actually, I mentioned 20mhx then later I mentioned 10 mhz - typo, corrected now.

 

[SpeedGeek]

@AndyLandy
The 060 only needs one clock so the 040 is the 68K family misfit! Also, it looks like GVP engineers out-smarted themselves and used quad clock generation on the Combo 040. I don't know if it was for a practical reason such as some part of the logic running @ 1/2 BCLK or just because they could do it that way.