patch: p4tcc and speedstep cpufreq drivers

Maxim Sobolev sobomax at
Sun Jul 3 00:37:04 GMT 2005

Nate Lawson wrote:
> Maxim Sobolev wrote:
>> Kevin Oberman wrote:
>>> No joy. I set it to 262 and it was fine. The next step killed the system
>>> again.
>>> I'm also concerned that taking TCC out of automatic mode might not be a
>>> great idea, at least until things like _PSV are supported. When I do a
>>> buildkernel, buildworld or any big compile job, I need to slow down the
>>> CPU to keep the CPU form frying. It quickly jumps to 185 F. or higher if
>>> I don't. If I understand automatic TCC, it should throttle the CPU all
>>> by itself to prevent this.
>> Taking TCC out of automatic mode doesn't disable thermal controlling 
>> circuitry completely, so that if the processor overheats it will shut 
>> down the machine anyway:
>> ---
>> Regardless of enabling of the automatic
>> or On-Demand modes, in the event of a catastrophic cooling failure, 
>> the processor will
>> automatically shut down when the silicon has reached a temperature of 
>> approximately
>> 135 °C. At this point the system bus signal THERMTRIP# will go active 
>> and stay active
>> until RESET# has been initiated. ---
> Correct.  Even more so, automatic mode continues to override On-Demand 
> mode if there is a more moderate thermal condition than THERMTRIP#:
> "On-Demand mode may be used at the same time Automatic mode is enabled, 
> however, if the system tries to enable the TCC via On-Demand mode at the 
> same time automatic mode is enabled AND a high temperature condition 
> exists, the duty cycle of the automatic mode will override the duty 
> cycle selected by the On-Demand mode."
> Since automatic mode is set by the BIOS before we even boot, things 
> should be fine.

Well, this is quite tricky part of the spec. My reading is that the 
paragraph above applies only to situation if you are trying to set 
on-demand mode when both automatic mode is in effect *and* high 
temperature condition already exists, in that case automatic mode will 
win and override any manual settings.

However, in the case when you have on-demand mode already on and high 
temperature condition emerges it will have no effect on duty cycle until 
THERMTRIP# kicks in.

That's in my view explains why there is big AND in the text above.

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