Speedstepping a Mac Mini
So I don’t forget this, and in case anyone else is trying to figure out how to slow a Mac down because it’s just too fast to be useful, here’s the solution: Stuart found an incantation the other day born in the CHUD tools for OS X. If you want to slow down a Mac (with the CHUD tools installed), run:
reggie_se -S 0b1100 -b 4:1 -i a -n IA32_CLOCK_MODULATION
the important bit there is the -S option (set) with 0b1100. The first 1 is to enable clock modulation, the “100″ corresponds to the following table:
000B Reserved 001B 12.5% (Default) 010B 25.0% 011B 37.5% 100B 50.0% 101B 63.5% 110B 75% 111B 87.5%
Oh, and one final note, you might want to take a snapshot of your registers before you begin using:
reggie_se -r -i a -n IA32_CLOCK_MODULATION
You can turn off speed-stepping by disabling the first bit in the first command (-S 0b0001 to set back to default), or, if you just want to be done with this nonsense, a reboot will get you back to starting state.
happy underclocking!
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