Hi,
this is a tweak to save power and reduce heat on pentium notebooks.
It should work on all Pentium MMX sytems, but i testet it only an my
Pentium MMX 200MHz notebook.
The Pentium has a feature called Autostandby. Each time the processor
gets a 'halt' instruction ( the kernel sends this during idle loops ),
the processor goes into a special standby mode, shutting down the parts
of the processor which are not needed. This saves a lot of power if
you are not doing CPU intensive stuff, where your pentium is idle most
of the time.
Unfortunately this feature is turned of in most notebooks by the bios.
It can be cotrolled via the MSR ( Machine Specific Register ). The following
lines of code just set one bit in these MSRs to 0, and thats all what is
necessary to enable this feature. There is one big drawback: It can not
be done from user space. So you have to put this into the kernel and rebuild
it. I put this into .../linux/arch/i386/kernel/setup.c at line 772, after
the part, where the pentium-III serial number is disabled. I'm not sure if this
is the correct place, but it works for me.
This works only for pentium-I mmx type of processors. There might be some
reason why this feature is disabled in most notebook. So be careful while
using this tweak. I do not take any responsible if this destroys anything
in your system.
{
unsigned long lo,hi;
rdmsr(0x0E,lo,hi);
lo &= ~0x40L;
wrmsr(0x0E,lo,hi);
printk(KERN_INFO "Additional Powersaving enabled.);
}
I sent this already to the powertweak guys and this will go into the
powertweak program, which is definately a better way to do stuff like
this. But its such a big improvement on my notebook ( it makes the
difference between fan running and fan not running and gives me at least
half an hour more battery life ), that i didn t want to hold it back.
hang loose
marcus
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