The K8V appears to tie the AGP frequency to the FSB with something like a
1:3 ratio. I can easily get my system to overclock to 220MHz FSB (AGP
73MHz) but any more and the graphics card (ATi 9800 Pro) takes the ball
home.
Does anyone know of a way to lock the AGP frequency at 66MHz please? This
will free-up all those lovely higher FSB options!
Regards,
Kayf
Please respond to group - e-mail address invalid
Every chipset is different, and with the Athlon64, I haven't read
or seen too much about clock architecture. (And, neither Via nor
Nvidia gives more than a fuzzy block diagram to the general public
for documentation, so that likely won't change.)
On Abxzone, there is mention that a lock could be implemented
in the BIOS (distant future?). To me, this implies that the
AGP clock could be a function of something inside the Northbridge.
I say this, because if the AGP clock was externally provided by
the clockgen, there would already be code in the BIOS to manipulate
any feature in a standard clockgen. So, using my crystal ball,
I predict that if AGP control is possible, it would be a programmable
down-divider off the FSB frequency. That means today the divider
is 3 (i.e. 200/3 = 66MHz AGP) and if any of the motherboard vendors
figure out how to program this theoretical divider in the
Northbridge, some day you might get 200/4 = 50MHz. Then, if the
clockgen is pushed to 260MHz, the AGP would be at 65MHz.
If you are in a mood to experiment, you could try dropping the
Hypertransport bus clock from 800MHz to 600MHz, on the off chance
that the AGP clock is divided down from HT, but that strikes me
as being unlikely to change anything. I have a suspicion that
as well, when you were doing your overclocking experiment, you
would have been overclocking the Hypertransport as well. At
220MHz FSB, the HT would have been at 880MHz. Maybe it is the
limiting factor ?
If AMD built your Northbridge, we'd have a datasheet to read
and could figure this out.
Hmmm... (Paul looks at the AMD site, just for fun.)
The second doc is the clockgen spec from AMD. Note that AMD doesn't
control the design of the Northbridge, so this doesn't guarantee any
implementation details, such as AGP lock or not in the Northbridge.
Board designers can ignore AMD if they want to.
http://www.amd.com/us-en/Processors/TechnicalResources/0,,30_182_739_7203,00.html
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/24707_PUB.PDF
ICST makes a lot of clock gen products - generally if Asus buys one,
they have a custom part number made (to prevent cloners from making
copies of the board), so again, this spec doesn't guarantee anything.
http://www.icst.com/products/summary/amd-frame.htm
http://www.icst.com/products/pdf/ics950402.pdf
Now, what looks interesting in the 950402 clockgen, is when 233MHz
processor is selected, "HTT" is at 66MHz. How about setting your
FSB to 233MHz, on the off chance that the K8V actually has a
3.5 divider available to it ?
HTH,
Paul
