22 Important Technology Information
Kontron User's Guide EPIC/CE
60
22.1.3
Processor Clock Throttling
The ACPI OS assesses the optimum CPU performance change necessary to lower the temperature using
the following equation:
Δ
P[%] = TC1(T
n
-T
n-1
) + TC2(T
n
-T
t
)
Δ
P is the performance delta, T
t
is the target temperature = critical trip point. The two coefficients TC1
and TC2 and the sampling period TSP are hardware-dependent constants that the end user must supply.
(See the setup options in the ACPI Control submenu of the BIOS Operation chapter).
You can control the cooling preference of the system by setting the appropriate trip points in the BIOS
setup.
Notes
: For more information, see Chapter 12 of the ACPI Specification.
22.2
I/O APIC vs. 8259 PIC Interrupt mode
The I/O APIC (Advanced Programmable Interrupt Controller) handles interrupts differently than the
8259 PIC. Enable the I/O APIC mode in the BIOS Setup Utility, if your operating system supports it.
Notes
: The APIC is not supported by all operating systems. Only Windows XP supports APIC.
Enable the APIC mode in the BIOS setup before the OS installation.
APIC only works in ACPI mode. For more detailed information about APIC, see:
Chapter 8 of the IA-32 Intel Architecture Software Developer’s Manual, Volume 3.
The following information explains these differences to the standard 8259 PIC mode:
Method of interrupts transmission
The I/O APIC transmits interrupts through the system bus. Interrupts are handled without the need for
the processor to run an interrupt-acknowledge cycle.
Interrupt priority
The priority of interrupts in the I/O APIC is independent of the interrupt number.
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