CPU temperatures question: NetBSD on iBook G3


macrumors member
Original poster
May 5, 2019
I don't know what the NetBSD guys did, but the problem with Xorg in older Radeon cards (https://forums.macrumors.com/threads/making-g3s-and-radeon-graphics-great-again.2191877/) is fixed there. Xorg runs fine. NetBSD, however, is painful; the installation has to be done manually, and it lacks lots of precompiled packages. However, at least it works.

I am having a very annoying problem with it. Randomly, the computer hits the maximum thermal treshold and shuts down:

*** FINAL System shutdown message from root@iBookG3 ***
System going down IMMEDIATELY

/etc/powerd/scripts//sensor_temperature: CRITICAL TEMPERATURE! SHUTTING DOWN.
This is baffling, since I always thought that the PowerPC 750FX had no thermal sensors. Linux always reported the temperature as (20 °C - Uncallibrated).

It seems like the system detects two different sensors: l_temp (described as "local chip temperature") and r1_temp ("CPU temperature"). l_temp in particular seems to have very weird defaults:

iBookG3# envstat
                          Current  CritMax  WarnMax  WarnMin  CritMin  Unit
[AC Adaptor]
             connected:      TRUE
              CPU Temp:     9.000                                      degC
                l_temp:    52.250   60.000                      0.000  degC
               r1_temp:    51.250   80.000                      0.000  degC
                  fan1:       N/A
As you can see, the system shuts down because l_temp hits 60 degrees Celsius, its maximum temperature. I don't even know what l_temp is, or where its sensor is located. But I think 60 degrees is a really low maximum.

And my question is, can I change the maximum temperature to, let's say, 80 degrees without frying the CPU? If the CPU gets to a dangerous temperature, it should automatically shutdown via hardware, right?
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macrumors 68000
Apr 19, 2014
You might find this site useful: https://tech.kateva.org/2004/09/ibook-temperature-monitor-and-g3.html

Essentially, some G3s and G4s had a "Thermal Assist Unit" which was supposed to read the on-die temp directly, but Motorola and IBM caution that it is very inaccurate (+/- 12-20 degrees Celsius) and requires calibration. The max temp for your CPU is probably around 105 Celsius, so I think you'd be safe with setting 80 as your limit. That gives you a 20 degree cushion in case the TAU is wildly off.