Raising temperature threshold

[Lowell Gilbert]

Matthew Flanagan <flanagan.matt at gmail.com> writes:

> I`ve installed a FreeBSD 5.4-STABLE and I was building some ports when 
> suddenly my system shut down. Upon rebooting it and checking 
> /var/log/messages, I found the following lines:
> 
> Jun 21 16:01:30 bell root: WARNING: system temperature too high,
> shutting down soon!
> Jun 21 16:01:40 bell kernel: acpi_tz0: WARNING - current temperature
> (60.0C) exceeds safe limits
> 
> Then I realized what had happened. My acpi_thermal sysctl's are:
> 
> hw.acpi.thermal.min_runtime: 0
> hw.acpi.thermal.polling_rate: 10
> hw.acpi.thermal.tz0.temperature: 50.0C
> hw.acpi.thermal.tz0.active: 0
> hw.acpi.thermal.tz0.thermal_flags: 1
> hw.acpi.thermal.tz0._PSV: 50.0C
> hw.acpi.thermal.tz0._HOT: -1
> hw.acpi.thermal.tz0._CRT: 60.0C
> hw.acpi.thermal.tz0._ACx: 50.0C -1 -1 -1 -1 -1 -1 -1 -1 -1
> 
> When I try to raise hw.acpi.thermal.tz0._CRT to 85C (which is the threshold in
> the BIOS setup) it doesn't work:
> 
> bell# sysctl hw.acpi.thermal.tz0._CRT=3580  # 3580 tenths of Kelvin=85C
> sysctl: oid 'hw.acpi.thermal.tz0._CRT' is read only
> 
> I've tried /etc/sysctl.conf as well, but I get the same error.
> 
> Now, my question is: how do I change this value? I've read several manpages
> (acpi(4), acpi_thermal(4), acpiconf(8), and many others) and checked the
> handbook, to no avail. Can anyone point me to the right direction?

Can it be set at boot time?  [from the loader?]