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- FSB---BIOS only?
September 3, 2006, 5:50 pm
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I have a naive question: does FSB frequency selection for overclocking
have to be done at BIOS time, or is it possible to alter it via a
privileged execution level after bootup time?
(this is particularly interesting in the case of something like the Mac
Pro, which does not have a BIOS, but EFI instead.)
Re: FSB---BIOS only?
It all depends on the clock generator chip. Many PC motherboards
use a clock generator chip that has a connection to the SMBUS.
By sending read and write operations on the SMBUS, it is possible
to change the settings of the clock generator. As you state, some
kind of driver with the appropriate level of privilege is needed
to gain access to the setting. On some systems, it can already
be present as an ACPI object. On others, third party programs
can be used to get at the hardware (as long as something is
done to make the hardware accessable, like the program includes
There is no perfectly generic system for doing this, and
support must be added to any runtime utility, as new hardware
is introduced. To give you an idea for how many clock generator
chips there are, take a look at the listing of chips here.
And this is just one supplier of clock generators:
http://www.icst.com/pdf/ (files beginning with ics...)
While this is a noble effort, the number of supported chips in
the list is pretty small, and the guy who wrote the program
had to sweat each one out. He needs hardware to test on, for
each one programmed.
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