Software underclocking

jeffleyda · Post by **jeffleyda** » Tue Feb 25, 2003 12:54 pm

Hi folks,

I've written a chunk of software (for DOS, sorry!) that uses a feature in the southbridge to enable STPCLK# going to to the CPU, effectively reducing the clock frequency going to the CPU.

From intel's ICH4 manual:

Throttling Using STPCLK#
Throttling is used to lower power consumption or reduce heat. The ICH4 asserts STPCLK# to
throttle the processor clock and the processor appears to temporarily enter a C2 state. After a
programmable time, the ICH4 deasserts STPCLK# and the processor appears to return to the C0
state. This allows the processor to operate at reduced average power, with a corresponding decrease
in performance.

Originally I wrote this to make today's CPUs run old games better, but there might be some people in this group interested in this method as an augment to hardware hacking.

I was working with my Epia M9000 last night, but I was unable to see any significant temperature decrease when I throttled my machine. Perhaps the C3 processor is immune to clock speeds affecting temperature because it's such a low power processor already. I dunno, this was my first attempt at using this program as a thermal management device.

My thinking was that the only real difference between the Epia 9000 and the 6000 was CPU speed, so perhaps throttling a 9000 down to 6000 speeds could allow for a fanless solution.

I'd be interested in any comments from people here.

the software can be obtained here:
http://www.waste.org/~winkles/throttle

thanks,
-jeff!

blakerwry · Post by **blakerwry** » Sun Mar 09, 2003 11:01 pm

Did you know that on VIA chipset motherboards the default is to ignore CPU HALT instructions... and not pass them to the CPU...

Will this affect your program?

Many people have overcome this by using H. Oda's wpcredit and wpcrset programs to modify registers of the motherboard(i believe on the N. Bridge) to recognize the HALT instructions.

For more info:
http://www.ocmodshop.com/default.aspx?a=125&p=266

jeffleyda · Post by **jeffleyda** » Wed Mar 12, 2003 10:30 am

blakerwry wrote:Did you know that on VIA chipset motherboards the default is to ignore CPU HALT instructions... and not pass them to the CPU...

Will this affect your program?

I was unaware of this, but no it won't effect my software.

All my code does is change the clock frequency going to the CPU.

Many people have overcome this by using H. Oda's wpcredit and wpcrset programs to modify registers of the motherboard(i believe on the N. Bridge) to recognize the HALT instructions.

For more info:
http://www.ocmodshop.com/default.aspx?a=125&p=266

This fascenating stuff. Looks like a tweak to the northbridge in the VIA chipset in order to enable HLTs. My code tweaks the southbridge, so perhaps collectively we could really cool the CPU down!

I should reiterate that my software, although it's a DOS program, can run in a windows dos shell just fine, especially ME/9x variants. Under NT/2k/XP, you'll need to download a driver, which is available on my site too.

http://www.waste.org/~winkles/throttle

Thanks for the information. I'm going to research this and perhaps come up with even more possibilities.

-jeff!