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NetBSD 6.1.5 - man page for acpitz (netbsd section 4)

ACPITZ(4)			   BSD Kernel Interfaces Manual 			ACPITZ(4)

     acpitz -- ACPI Thermal Zone

     acpitz* at acpi?

     The acpitz driver supports so-called ACPI ``Thermal Zones''.  The temperature can be moni-
     tored 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.

     The acpitz driver knows about the active cooling levels, the current temperatures, and crit-
     ical, 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

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

     The acpitz driver appeared in NetBSD 2.0.

     Jared D. McNeill <jmcneill@invisible.ca>

     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.

BSD					 January 9, 2011				      BSD

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