FIC A360 service manual Passive Cooling Equation, Critical Shutdown, Software Functional Overview

Software Functional Overview

3.5.15 Passive Cooling Equation

Unlike the case for _ACx, during passive cooling the OS takes the initiative to actively monitor the temperature in order to cool the platform. On an ACPI-compatible platform that properly implements CPU throttling, the temperature transitions will be similar to the following figure.

Temperature	Tn - 1	ΔP
		Tn
Tt
	_TSP (Sampling period)
		Time

100%

CPU Performance

50%

Figure 3-4 Temperature and CPU Performance Versus Time

For the OS to assess the optimum CPU performance change required to bring the temperature down, the following equation must be incorporated into the OS.

ΔP [%] = _TC1 * ( Tn - Tn-1 ) + _TC2 * (Tn - Tt)

where

Tn = current temperature

Tt = target temperature (_PSV)

The two coefficients _TC1 and _TC2 and the sampling period _TSP are hardware-dependent constants the OEM must supply to the OS (for more information, see section 12.3). The object _TSP contains a time interval that the OS uses to poll the hardware to sample the temperature. Whenever _TSP time has elapsed, the OS will run _TMP to sample the current temperature (shown as Tn in the above equation). Then the OS will use the sampled temperature and _PSV (which is the target temperature Tt) to evaluate the equation for ΔP. 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.

3.5.16 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.

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