Underclocking FSB on an XP 2100+ / KT266A mobo?

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Here's the deal:  I've got a (old, yes) DFI AD70-SR mobo, with the Via
KT266A chipset, and an Athlon XP 2100+ CPU running at 1.70 volts (down
from the spec 1.75).

For various reasons (less heat, noise, power, and just to see if it can
be done), I'd like to try to go lower than 1.70v, but the system's not
stable at less than that. So I'd like to try to lower the FSB frequency
slightly to see if I can find a sweet spot on the performance/power

The problem is that the BIOS on this board doesn't allow an FSB setting
less than the stock 133mhz, and the various utilities I've tried
(SoftFSB and CPUFSB, iirc) both say "PLL read error" or something
similar when I try to set the FSB speed with them - even though (1)
I've identified the PLL correctly (a Cypress W312-02H) to them and (2)
they both *read* all the frequencies from the PLL just fine (showing
the processor at 1730mhz and the fsb at 133mhz). It's just the setting
function that doesn't seem to work. (I know the PLL can go lower than
133, btw, from reading the spec sheets on it.)

I'm posting on the off chance anyone has experience with this
particular board, chipset, or PLL who can suggest something worth
trying. Thanks.


Re: Underclocking FSB on an XP 2100+ / KT266A mobo?

On Mon, 22 May 2006 10:15:01 -0700, David  Ruggiero wrote:

Quoted text here. Click to load it
Change the default on the cpu itself.


BTW, according to the AD70-SR manual, JP7 controls default FSB speed.
Selections are 100MHz and 133MHz. And you can also set it in the bios (CPU
Host/PCI Clock setting)

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Re: Underclocking FSB on an XP 2100+ / KT266A mobo?

Thanks. The page you referenced at fab51.com doesn't apply to my
processor (it's a Palomino, not a T-bird or Barton, so the CPU traces
are a bit different) ), but the other info was good - setting jumper
jp7 on the mobo allowed me to access clock settings from 100-132mhz
where formerly I could only get 133-255mhz. I'll do some playing around
with bus speeds and CPU voltages now...

thanks /david/

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