Fan control for PowerMac7_3 (#3)

H. Peter Anvin hpa at
Sun Oct 17 10:58:22 EST 2004

Paul Mackerras wrote:
> H. Peter Anvin writes:
>>It's the backside fan that oscillates; backside_fan_pwm varies between 
>>30 and 100 in what is pretty much a squarewave.  See attached graph (and 
>>note how the other fans vary with workload.)
> The sharp rises look like the code thinks it gets into an
> over-temperature situation and turns the fans on full blast.  It could
> be worth putting some printks in the overtemp code.

Changing the unsigned variables to signed per Ben's suggestion seems to 
have solved the problem.

>>I probably need to write a "power virus" program for the G5 to really 
>>test out the high end (a power virus is a program which keeps the chip 
>>running as hard as it can; generally keep all pipelines stuffed.)
> Hmmm, I should see if I can dig such a thing out of somewhere in IBM.

That would be good; otherwise they're not too hard to write given a 
microarchitectural description.


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