82374EB Datasheet, PDF (93/208 Pages) Intel Corporation – SYSTEM COMPONENT (ESC)

82374EB 82374SB
3 7 APIC Registers
This section describes the registers used to program the Advanced Programmable Interrupt Controller The
I O APIC registers are accessed by an indirect addressing scheme using two registers (IOREGSEL and
IOWIN) that are located in the CPU’s memory space (memory address specified by the APICBASE Register)
To reference an I O APIC register a Dword memory write loads the IOREGSEL Register with a 32-bit value
that specifies the APIC register The IOWIN Register then becomes a four byte window pointing to the APIC
register specified by bits 7 0 of the IOREGSEL Register The register address table is shown in the Address
Decode section
All APIC registers are accessed using 32-bit loads and stores This implies that to modify a field (e g bit byte)
in any register the whole 32-bit register must be read the field modified and the 32-bits written back In
addition registers that are described as 64-bits wide are accessed as multiple independent 32-bit registers
3 7 1 IOREGSEL I O REGISTER SELECT REGISTER
Memory Address FEC0 x000h (82374EB) (x^eSee APICBASE Register)
FEC0 xy00h (82374SB) (xy^eSee APICBASE Register)
Default Value
Attribute
Size
00h
Read Write
32 Bits
This register selects an I O APIC Unit register The contents of the selected 32-bit register can be manipulated
via the I O Window Register
Bit
Description
31 8 Reserved
7 0 APIC Register Address Bits 7 0 specify the APIC register to be read written via the IOWIN
Register
3 7 2 IOWIN I O WINDOW REGISTER
Memory Address FEC0 x010h (82374EB) (x^eSee APICBASE Register)
FEC0 xy10h (82374SB) (xy^eSee APICBASE Register)
Default Value
Attribute
Size
00h
Read Write
32 Bits
This register is mapped onto the I O Unit’s register selected by the IOREGSEL Register Readability writability
by software is determined by the I O APIC register that is currently selected
Bit
Description
31 0 APIC Register Data Memory references to this register are mapped to the APIC register specified
by the contents of the IOREGSEL Register
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