overclock & speedstep

[trx]

I had tested AMD Athlon64 (Winchester core) and found out how PowerNow controls Vcore.
I've been manualy overriding Frequency/Voltage pairs on it to undervolt it in both 1.8 and 1.0GHz states.

Is it the same with Intel SpeedStep?


If it's the same, this scenario would be right:

CPU boots with Vcore that is set in the BIOS.
SpeedStep reads Frequency(Multiplier)/Vcore table from BIOS and uses it.

E6300 @ default:
7 x 266MHz (1.86GHz) ~1.35V on the full load
6 x 266MHz (1.60GHz) ~1.15V in the idle state

so, if I raise FSB to 400MHz I get:
7 x 400MHz (2.80GHz) ~1.35V on the full load
6 x 400MHz (2.40GHz) ~1.15V in the idle state

So, my CPU has to be stable in both situations: 2.8GHz @1.35V and 2.4GHz @1.15V
Guess it's the main "stability" problem if SpeedStep is on while overclocking. Guess it's more difficult to get it run stable @1.15V with mulitplier 6 than @1.35V with multiplier 7.

Another thing:
If I raise Vcore to ~1.45V in the BIOS, and set some high CPU freq that can not be achieved with ~1.35V, when SpeedStep kicks in it will read Multiplier/Vcore table from BIOS and NOT Vcore I've set manualy. So, it will use 1.15 and 1.35V for multiplliers 6 and 7 and bring instability on that high frequencies.


So, anyone with Intel Core 2 Duo, is the process the same ?

 

[trx]

anyone?

 

[zach0624]

Usually you turn off speedstep because it undervolts the idle state too much and can cause instability unless you tweak your system from what I've heard, I haven't bothered turning it on yet. I am not sure how much power savings you get from having speedstep on, but unless you are really concerned with a couple of dollars on your annual total(and I mean <10) then it is usually not worth getting it stable with that.

 

[trx]

I'd like to minimize heat disipation and be able to cool CPU passively most of the time. that's why I'm asking...

 

[zach0624]

Ok if you're going to oc and want to minimize heat on idle it might be worth a try you could be able to get some pretty good results with speedstep just make sure that it doesn't get undervolted to much or you might lose stability running on idle for a while, but if you tweak it it should give you a pretty good oc still.

 

[nyker96]

just try it on first, with my setup I OC to about 3Ghz@1.325v with speed step it turn it down to about 2Ghz@1.075v at idle and I don't lose stability. so if you get it working, then you can keep the rig cooler. try it to see if works for your OCed setting. it just might.

 

[trx]

thx everybody for your replies.

I've been thinking about some moderate overclocking without the need for changing voltages @idle nor @full load. I know core2duo can overclock well up to 3GHz and beyond with default voltage (I consider e6550 & e6750), but I would like to use speedstep to be able to passively cool CPU most of the time.

with winchester, I've made graph of voltage needed to operate stable (prime95 & stuff). from that graph I've decided it's safe to run it 1GHz@1.000V and 1.8GHz@1.275V - I've added 0.1V to achieve "110%" stability.

http://img516.imageshack.us/im...2444/winchesterfq7.png

voltage on max load was lowered for 0.125V, but it had big impact on thermal disipation.

another interesting fact is that with default settings, C'n'Q drops voltage to 1.1V for 1.0GHz and my measurement showed that CPU is stable up to 1.6GHz with that voltage.
that means I could (theoreticly, if 1.4V default voltage is enough) overclock it to 2880MHz (9x320MHz) and when C'n'Q drops multiplier to 5x I would have stable idle system at 1.6GHz.

so, with AMD lowest multiplier/voltage wasn't the problem. highest mulitiplier would rich CPU's limit first.


with core2duo I'll try to find that sweet spot where I can run speedstep stable with (a little bit) overclocked CPU.
I'll just have to find max frequency my core2duo can run stable @1.15V as that is the voltage it runs with multiplier 6.

 

[cmdrdredd]

I always turn it off because I don't want my system to clock down. I'm pretty much always using the CPU when the PC is on.

 

[trx]

I use my box in many ways. often it plays music, movies or just stays turned on to check mail periodicly or download something during the night.