Jochen Voss <voss@seehuhn.de> writes: > Hi, > > On Mon, Mar 28, 2005 at 12:40:27PM +0930, John Steele Scott wrote: >> cpufreq drivers for ppc only support two speeds at the moment. So if you ask >> for 200MHz, it will still give you 750MHz. > I think that this is a hardware property of the CPU and not a property > of the driver (at least for the 7447A CPU). So it will ever be only > two frequencies. Aye, this is correct, but it is also true that most of these chips have a feature called instruction cache throttling. When this is enabled, you can achieve effective frequencies as low as slow_freq/N, where N is between 2 and 256. The CPU is still clocked at the same frequency, but the instruction cache only gives a real instruction every Nth clock cycle. The rest of the time the CPU is executing NOPs, so many of the functional units will be powered down. cheers, John
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