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Re: [PATCH] hp-timing for ppc32/64


Note that some CPUs like the 970 can have an externally clocked
timebase. Apple uses this feature to make the CPU immune to bus/cpu
frequency slewing, they use a 33Mhz clock for that.


The 970 does not implement a alternate timebase. So for 970 the timebase

is the highest frequency counter available.
It seems that Apple choose 33MHz to meet the minimum (slowest)CPU- clock
/
32 timebase. But that was their choice. The IBM hardware seems to be
holding to the CPU_clock / 8 timebase (including 970 based JS20).

One could argue that the performance monitors could be used as a cycle counter on 970 :)


- kumar


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