ACPITZ(4)               NetBSD 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 temper-
     ature 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 consump-
            tion 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 consump-
            tion 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 tem-
     peratures, and critical, hot, and passive temperature thresholds (as sup-
     ported 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 crit-
     ical 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 <jmcneill@invisible.ca>

CAVEATS
     While no pronounced bugs are known to exist, several caveats can be men-
     tioned:

        Passive cooling is not implemented.

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

        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 7.0                      January 9, 2011                     NetBSD 7.0

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