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ACPITZ(4)                  Kernel Interfaces Manual                  ACPITZ(4)

NAME
     acpitz -- ACPI Thermal Zone

SYNOPSIS
     acpitz* at acpi?

DESCRIPTION
     The acpitz driver supports so-called ACPI ``Thermal Zones''.  The
     temperature can be monitored by the envsys(4) API or the envstat(8)
     command.

     The distinction between ``active'' and ``passive'' cooling is central to
     the abstractions behind acpitz.  These are inversely related to each
     other:

       1.   Active cooling means that the system increases the power
            consumption of the machine by performing active thermal management
            (for example, by turning on a fan) in order to reduce the
            temperatures.

       2.   Passive cooling means that the system reduces the power
            consumption of devices at the cost of system performance (for
            example, by lowering the CPU frequencies) in order to reduce the
            temperatures.

     Only active cooling is currently supported on NetBSD.

     It should be also noted that the internal functioning of these cooling
     policies vary across machines.  On some machines the operating system may
     have little control over the thermal zones as the firmware manages the
     thermal control internally, whereas on other machines the policies may be
     exposed to the implementation at their full extent.

EVENTS
     The acpitz driver knows about the active cooling levels, the current
     temperatures, and critical, hot, and passive temperature thresholds (as
     supported by the hardware).  The driver is able to send events to
     powerd(8) when the sensor's state has changed.  When a Thermal Zone is
     either critical or ``hot'', the /etc/powerd/scripts/sensor_temperature
     script will be invoked with a critical-over event.

     The critical temperature is the threshold for system shutdown.  Depending
     on the hardware, the mainboard will take down the system instantly and no
     event will have a chance to be sent.

SEE ALSO
     acpi(4), acpifan(4), envsys(4), envstat(8), powerd(8)

HISTORY
     The acpitz driver appeared in NetBSD 2.0.

AUTHORS
     Jared D. McNeill <jmcneillATinvisible.ca>

CAVEATS
     While no pronounced bugs are known to exist, several caveats can be
     mentioned:

     o   Passive cooling is not implemented.

     o   There is no user-controllable way to switch between active and
         passive cooling, although the specifications support such transforms
         on some machines.

     o   The ``hot'' temperature is a threshold in which the system ought to
         be put into S4 sleep.  This sleep state (``suspend to disk'') is not
         supported on NetBSD.

NetBSD 6.1.5                    January 9, 2011                   NetBSD 6.1.5