User manual

Kontron Compact Computers AG SMX945 Detailed Manual V1.1
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8.2.2. The SMX945 ACPI Thermal Solution
The SMX945 ACPI Thermal Solution offers three different cooling policies:
8.2.2.1. Passive Cooling
When the temperature in the thermal zone must be reduced, the operating system can decrease the power
consumption of the processor by throttling the processor clock. One of the advantages of this cooling policy
is that passive cooling devices (in this case the processor) do not produce any noise. Use the “passive
cooling trip point” setup node in the BIOS setup program to determine the temperature threshold that the
operating system will use to start or stop the passive cooling procedure.
8.2.2.2. Active Cooling
During this cooling policy the operating system is turning the fan on/off. Although active cooling devices
consume power and produce noise, they also have the ability to cool the thermal zone without having to
reduce the overall system performance. Use the “active cooling trip point” setup node in the BIOS setup
program to determine the temperature threshold that the operating system will use to start or stop the active
cooling device.
8.2.2.3. Critical Trip Point
If the temperature in the thermal zone reaches a critical point then the operating system will perform a
system shut down in an orderly fashion in order to ensure that there is no damage done to the system as a
result of high temperatures. Use the “critical trip point” setup node in the BIOS setup program to determine
the temperature threshold that the operating system will use to shut down the system.
8.2.3. Implementation
The end user must determine the cooling preferences for the system by using the setup nodes in the BIOS
setup program to establish the appropriate trip points. If passive cooling is activated and the processor
temperature is above the trip point the processor clock is throttled according to the formula below.
∆P[%] = TC1(Tn-Tn-1) + TC2(Tn-Tt)
∆P is the performance delta.
Tt is the target temperature = critical trip point.
The two coefficients, TC1 and TC2, and the sampling period (TSP) are hardware-dependent constants.
These constants are set to fixed values for the SMX945:
TC1 = 1 TC2 = 5 TSP = 5sec.