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:
- 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.
- 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
<
jmcneill@invisible.ca>
CAVEATS
While no pronounced bugs are known to exist, several caveats can be mentioned:
- Passive cooling is not implemented.
- There is no user-controllable way to switch between
active and passive 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.