Re: Processor Temperature
Re: Processor Temperature
- Subject: Re: Processor Temperature
- From: "William Kucharski" <email@hidden>
- Date: Mon, 19 Jan 2004 06:28:40 -0700
Robert J. Accettura said:
>
Well, I found some info here:
>
http://e-www.motorola.com/files/32bit/doc/app_note/AN1800.pdf
>
>
But I'm missing something :-( I guess. Most likely licensing is in the
>
way. Perhaps someone knows better.
That app note brings up several good points.
1) The TAU in the Motorola CPUs is only considered reasonably accurate in the
MPC750 (Motorola G3.)
2) Each individual CPU MUST be calibrated for the numbers returned by the TAU
to resemble reality at all; the calibration range provided for means the
TAU can be off +/- 34 degrees C.
3) Chip errata for the MPC74XX (Motorola G4) family note that Motorola
essentially dropped support for the TAU in the 74XX family of CPUs, as
it may report erroneous values in the MPC7450 and MPC7455 CPUs and is
not even implemented in the MPC7457.
See Errata No. 3 in the MPC74XX family errata:
http://e-www.motorola.com/files/32bit/doc/errata/MPC7457CE.pdf
4) IBM has STILL not published a CPU-specific manual for the PPC970, so we
have no idea what may or may not be supported on the G5.
In short, the TAU is useless on any CPU other than a G3, and even then all
you can really tell is RELATIVE rather than ABSOLUTE temperature without
first calibrating each individual CPU using the techniques given in the
Motorola app note you referenced.
William Kucharski
email@hidden
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