ACPITZ(4)						   BSD 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) com-
     mand.

     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 exam-
	    ple, 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 low-
	    ering 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 <jmcneill@invisible.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.

BSD
								  January 9, 2011							       BSD