LPC Interface Bridge Registers (D31:F0)
494 Datasheet
13.5.3 DAT—Data Register
Memory Address FEC_ _0000h Attribute: R/W
Default Value: 00000000h Size: 32 bits
This is a 32-bit register specifying the data to be read or written to the register pointed
to by the Index register. This register can only be accessed in DWord quantities.
13.5.4 EOIR—EOI Register
Memory Address FEC_ _0000h Attribute: R/W
Default Value: N/A Size: 32 bits
The EOI register is present to provide a mechanism to maintain the level triggered
semantics for level-triggered interrupts issued on the parallel bus.
When a write is issued to this register, the I/O APIC will check the lower 8 bits written
to this register, and compare it with the vector field for each entry in the I/O
Redirection Table. When a match is found, the Remote_IRR bit (Index Offset 10h, bit
14) for that I/O Redirection Entry will be cleared.
Note: If multiple I/O Redirection entries, for any reason, assign the same vector for more
than one interrupt input, each of those entries will have the Remote_IRR bit reset to 0.
The interrupt, which was prematurely reset, will not be lost because if its input
remained active when the Remote_IRR bit was cleared, the interrupt will be reissued
and serviced at a later time. Note that only bits 7:0 are actually used. Bits 31:8 are
ignored by the PCH.
Note: To provide for future expansion, the processor should always write a value of 0 to Bits
31:8.
Bit Description
7:0
APIC Data — R/W. This is a 32-bit register for the data to be read or written to the
APIC indirect register (Figure 13-5) pointed to by the Index register (Memory Address
FEC0_0000h).
Bit Description
31:8
Reserved. To provide for future expansion, the processor should always write a value of
0 to Bits 31:8.
7:0
Redirection Entry Clear — WO. When a write is issued to this register, the I/O APIC
will check this field, and compare it with the vector field for each entry in the I/O
Redirection Table. When a match is found, the Remote_IRR bit for that I/O Redirection
Entry will be cleared.
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