FIC M296 - Manual (Page 81)

Software Functional Overview
The granularity of
ΔP is determined by the CPU duty width of the system. A detailed
explanation of this thermal feedback equation is beyond the scope of this specification.
3.6.6 Critical Shutdown
When the heat reaches the temperature indicated by _CRT, the OS must immediately
shutdown the system. The system must disable the power either after the temperature reaches
some hardware-determined level above _CRT or after a predetermined time has passed.
Before disabling power, platform designers should incorporate some time that allows the OS
to run its critical shutdown operation. There is no requirement for a minimum shutdown
operation window that commences immediately after the temperature reaches _CRT. This is
because
− Heat might rise rapidly in some systems and slower on others, depending on casing
design and environmental factors.
− Shutdown can take several minutes on a server and only a few short seconds on a
hand-held device.
Because of this indistinct discrepancy and the fact that a critical heat situation is a remarkably
rare occurrence, ACPI does not specify a target window for a safe shutdown. It is entirely up
to the OEM to build in a safe buffer that it sees fit for the target platform.
3.6.7 Other Implementation of Thermal Controllable
Devices
The ACPI thermal event model is flexible enough to accommodate control of almost any
system device capable of controlling heat. For example, if a mobile PC requires the battery
charger to reduce the charging rate in order to reduce heat it can be seamlessly implemented
as an ACPI cooling device. Associating the charger as an active cooling device and reporting
to the OS target temperatures that will enable or disable the power resource to the device do
this. Figure as following illustrates the implementation. Because the example does not create
noise, this will be an implementation of silence mode.
5
10
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_AC0
_PSV
_CRT
_AC1
Throttle CPU
Fan on/off
Reduce charge
rate
FIC M295 / M296 Service Manual
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