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Software Functional Overview
z Battery Control Methods
Object Description
_BIF Return static information about a battery (i.e., model number, serial
number, design voltage, etc.)
_BST Returns the current battery status (i.e., dynamic information about the
battery such as whether the battery is currently charging, an estimate of
the remaining battery capacity, etc.).
_BTP Sets the Battery Trip point, which generates an SCI when the battery(s)
capacity reaches the specified point
_PCL List of pointers to the device objects representing devices powered by the
battery.
_STA Returns general status of the battery (for a description of the _STA control
method.
3.6.2 Thermal Control
ACPI allows OS to be proactive in its system cooling policies. With OS in control of the
operating environment, cooling decisions can be made based on application load on the CPU
and the thermal heuristics of the system. Graceful shutdown of OS at critical heat levels
becomes possible as well. The following sections describe the thermal objects available to OS
to control platform temperature. ACPI expects all temperatures to be given in tenths of
Kelvin.
The ACPI thermal design is based around regions called thermal zones. Generally, the entire
PC is one large thermal zone, but an OEM can partition the system into several thermal zones
if necessary.
z Active, Passive, and Critical Policies
There are three primary cooling policies that the OS uses to control the thermal state of the
hardware. The policies are Active, Passive and Critical:
− Passive cooling: The OS reduces the power consumption of the system to reduce the
thermal output of the machine by slowing the processor clock. The _PSV control
method is used to declare the temperature to start passive cooling.
− Active cooling: The OS takes a direct action such as turning on a fan. The _ACx
control methods declare the temperatures to start different active cooling levels.
− Critical trip point: This is the threshold temperature at which the OS performs an
orderly, but critical, shut down of the system. The _CRT object declares the critical
temperature at which the OS must perform a critical shutdown.
When a thermal zone appears, the OS runs control methods to retrieve the three temperature
points at which it executes the cooling policy. When the OS receives a thermal SCI it will run
the _TMP control method, which returns the current temperature of the thermal zone. The OS
checks the current temperature against the thermal event temperatures. If _TMP is greater
than or equal to _ACx then the OS will turn on the associated active cooling device(s). If
_TMP is greater than or equal to _PSV then the OS will perform CPU throttling. Finally if
_TMP is greater than or equal to _CRT then the OS will shutdown the system.
FIC M295 / M296 Service Manual 3-27