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Re: Pismo status

At 7:48 AM -0700 5/18/00, Tim Wojtulewicz wrote:
On Wed, 17 May 2000, Timothy A. Seufert wrote:

 No, it will not.

 The PowerPC 750 (G3) and 7400 (G4) can both fire off an interrupt
 when the on-die temperature sensor reading rises above a trigger
 value (or falls below a second trigger value).  This feature *could*
 be used by an operating system to slow down the CPU (through the
 instruction cache throttling feature) or halt it to prevent
 overheating.  However, there is no hardware feature which can halt
 the CPU without software control.

So in other words, without a little bit of help from the OS, the fan won't
come on when it the temperature hits this trigger value.  The temperature
would of course, continue to rise.

This die temperature sensor has nothing to do with the PowerBook's fan. It's built into all PPC 750 and 7400 CPUs.

Apple could use the die sensor to control the fan, but instead they use a sensor on the motherboard of the PowerBook, as the fan is really intended to ensure that the ambient temperature inside the whole PowerBook doesn't get too hot. This because there are actually things which are much more sensitive to overheating than the CPU, like the hard drive.

Has any code been written for LinuxPPC that will let us monitor this
sensor?  I know there's a whole lm_sensors package for i386 and the like,
but is there something like this for us?

For some PowerBooks / PMU versions, I think so. We will probably get full support for things like this when Apple puts it into Darwin/OS X.

Yes, I had heard they upgraded the PMU, but I wasn't aware of how much
they had changed it.  Is it just a matter of knowing some extra bits we
can switch on and off in the PMU, or is it more than that?

Probably more than that, but I don't know anything beyond the basic fact that the PMU (both the hardware and its control program) got the first major upgrade in years.

  Tim Seufert

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