underclock prob with a P4C800 deluxe

[Alban Brument]

Hello,
I have a P4C800 deluxe mainboard with the last bios (1021) coupled to a P4C
2.4 ghz not overclocked and 2x 512 mo (corsair memory)
For some reasons of heating and thus of noise, I want tried to decrease the
fsb from 200 to 175 on a purely experimental basis.
it goes without problem with clockgen which makes it possible to change the
fsb under Windows but on the level of the bios with an fsb <=199, I have
crash on the level of the bios which announces to me with the failure
because of overclocking ?
With an FSB >200, i have no problem ? it is rather strange!

Thank you in advance
A. Brument

 

[Mercury]

if you want to drop temp. consider also dropping cpu voltage at the same
time.
please keep us posted. I am particularly interested as I have servers that I
want running 24 x 7, but not with the noise and heat issues...

 

[Paul]

Hello,
I have a P4C800 deluxe mainboard with the last bios (1021) coupled to a P4C
2.4 ghz not overclocked and 2x 512 mo (corsair memory)
For some reasons of heating and thus of noise, I want tried to decrease the
fsb from 200 to 175 on a purely experimental basis.
it goes without problem with clockgen which makes it possible to change the
fsb under Windows but on the level of the bios with an fsb <=199, I have
crash on the level of the bios which announces to me with the failure
because of overclocking ?
With an FSB >200, i have no problem ? it is rather strange!

Thank you in advance
A. Brument

There is an interesting theory on Abxzone.

http://www.abxzone.com/forums/showthread.php?s=&threadid=59662

Most people are familiar with the CPU clock and the Memory
clock which is derived from it. But there is a third clock,
which controls the North/South bus. That Abxzone thread
claims that at 200MHz, the chipset bus is (200/3)*4=266MB/sec,
which is the nominal speed seen in the datasheet. But at
199MHz, the Abxzone thread claims the clock is (199/2)*4=396MB/sec.

When I look at page 142 of the 875 Northbridge datasheet:

http://developer.intel.com/design/chipsets/datashts/25252501.pdf

it mentions that the hub clock and the AGP clock are supposed to
be synchronous. And that makes me wonder whether the Abxzone
claims are accurate or not.

So, I have a suggestion for you.

*****
Select "AI Overclock Tuner" [Standard] in the BIOS.

Once [Standard] is selected above, set "AGP/PCI Frequency" to
[66.66/33.33] instead of [Auto].

Then try your CPU clock of 199MHz again and see what happens.
*****

Maybe that will force the AGP and Hub bus clocks to 66.66MHz, and
prevent overclocking of the North/South bus when CPU clock is set
to 199MHz. (The only way to really know what is happening, is
to connect a frequency counter to the chips.)

ICS has datasheets for _some_ of their clock generators,
available for public download. I don't know if this datasheet
is for the chip used on your motherboard, but in any case, you
might get some more info as to how the clock generator chip works,
by looking at this:

http://www.icst.com/products/pdf/ics952607.pdf

Also, setfsb is mentioned here, if you don't already have a copy:
http://www.abxzone.com/forums/showthread.php?threadid=42602

Just a theory,
Paul

 

[Alban Brument]

thx very much for your complete response,
i will try

Hello,
I have a P4C800 deluxe mainboard with the last bios (1021) coupled to a P4C
2.4 ghz not overclocked and 2x 512 mo (corsair memory)
For some reasons of heating and thus of noise, I want tried to decrease the
fsb from 200 to 175 on a purely experimental basis.
it goes without problem with clockgen which makes it possible to change the
fsb under Windows but on the level of the bios with an fsb <=199, I have
crash on the level of the bios which announces to me with the failure
because of overclocking ?
With an FSB >200, i have no problem ? it is rather strange!

Thank you in advance
A. Brument

There is an interesting theory on Abxzone.

http://www.abxzone.com/forums/showthread.php?s=&threadid=59662

Most people are familiar with the CPU clock and the Memory
clock which is derived from it. But there is a third clock,
which controls the North/South bus. That Abxzone thread
claims that at 200MHz, the chipset bus is (200/3)*4=266MB/sec,
which is the nominal speed seen in the datasheet. But at
199MHz, the Abxzone thread claims the clock is (199/2)*4=396MB/sec.

When I look at page 142 of the 875 Northbridge datasheet:

http://developer.intel.com/design/chipsets/datashts/25252501.pdf

it mentions that the hub clock and the AGP clock are supposed to
be synchronous. And that makes me wonder whether the Abxzone
claims are accurate or not.

So, I have a suggestion for you.

*****
Select "AI Overclock Tuner" [Standard] in the BIOS.

Once [Standard] is selected above, set "AGP/PCI Frequency" to
[66.66/33.33] instead of [Auto].

Then try your CPU clock of 199MHz again and see what happens.
*****

Maybe that will force the AGP and Hub bus clocks to 66.66MHz, and
prevent overclocking of the North/South bus when CPU clock is set
to 199MHz. (The only way to really know what is happening, is
to connect a frequency counter to the chips.)

ICS has datasheets for _some_ of their clock generators,
available for public download. I don't know if this datasheet
is for the chip used on your motherboard, but in any case, you
might get some more info as to how the clock generator chip works,
by looking at this:

http://www.icst.com/products/pdf/ics952607.pdf

Also, setfsb is mentioned here, if you don't already have a copy:
http://www.abxzone.com/forums/showthread.php?threadid=42602

Just a theory,
Paul

 

[Alban Brument]

thank you very much : your suggestion was good : with forcing the agp to 66
mhz instead of auto, the prob have dispeared !

thank you very much

Hello,
I have a P4C800 deluxe mainboard with the last bios (1021) coupled to a P4C
2.4 ghz not overclocked and 2x 512 mo (corsair memory)
For some reasons of heating and thus of noise, I want tried to decrease the
fsb from 200 to 175 on a purely experimental basis.
it goes without problem with clockgen which makes it possible to change the
fsb under Windows but on the level of the bios with an fsb <=199, I have
crash on the level of the bios which announces to me with the failure
because of overclocking ?
With an FSB >200, i have no problem ? it is rather strange!

Thank you in advance
A. Brument

There is an interesting theory on Abxzone.

http://www.abxzone.com/forums/showthread.php?s=&threadid=59662

Most people are familiar with the CPU clock and the Memory
clock which is derived from it. But there is a third clock,
which controls the North/South bus. That Abxzone thread
claims that at 200MHz, the chipset bus is (200/3)*4=266MB/sec,
which is the nominal speed seen in the datasheet. But at
199MHz, the Abxzone thread claims the clock is (199/2)*4=396MB/sec.

When I look at page 142 of the 875 Northbridge datasheet:

http://developer.intel.com/design/chipsets/datashts/25252501.pdf

it mentions that the hub clock and the AGP clock are supposed to
be synchronous. And that makes me wonder whether the Abxzone
claims are accurate or not.

So, I have a suggestion for you.

*****
Select "AI Overclock Tuner" [Standard] in the BIOS.

Once [Standard] is selected above, set "AGP/PCI Frequency" to
[66.66/33.33] instead of [Auto].

Then try your CPU clock of 199MHz again and see what happens.
*****

Maybe that will force the AGP and Hub bus clocks to 66.66MHz, and
prevent overclocking of the North/South bus when CPU clock is set
to 199MHz. (The only way to really know what is happening, is
to connect a frequency counter to the chips.)

ICS has datasheets for _some_ of their clock generators,
available for public download. I don't know if this datasheet
is for the chip used on your motherboard, but in any case, you
might get some more info as to how the clock generator chip works,
by looking at this:

http://www.icst.com/products/pdf/ics952607.pdf

Also, setfsb is mentioned here, if you don't already have a copy:
http://www.abxzone.com/forums/showthread.php?threadid=42602

Just a theory,
Paul