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82801AA and 82801AB Datasheet
8-41
LPC Interface Bridge Registers (D31:F0)
8.5.6
ARBID—Arbitration ID Register
Index Offset:
Default Value:
02h
00000000h
Attribute:
Size:
RO
32 bits
This register contains the bus arbitration priority for the APIC. This register is loaded whenever the
APIC ID register is loaded. A rotating priority scheme is used for APIC bus arbitration. The winner
of the arbitration becomes the lowest priority agent and assumes an arbitration ID of 0.
a
8.5.7
Redirection Table
Index Offset:
10h
–
11h (vector 0) through
3E
–
3Fh (vector 23)
Bit 16-‘1’, Bits[15:12]=’0’.
All other bits undefined
Attribute:
R/W
Default Value:
Size:
64 bits each, (accessed as
two 32 bit quantities)
The Redirection Table has a dedicated entry for each interrupt input pin. The information in the
Redirection Table is used to translate the interrupt manifestation on the corresponding interrupt pin
into an APIC message.
The APIC will respond to an edge triggered interrupt as long as the interrupt is held until after the
acknowledge cycle has begun. Once the interrupt is detected, a delivery status bit internally to the
I/O APIC is set. The state machine steps ahead and waits for an acknowledgment from the APIC
bus unit that the interrupt message was sent over the APIC bus. Only then is the I/O APIC able to
recognize a new edge on that interrupt pin. That new edge only results in a new invocation of the
handler if its acceptance by the destination APIC causes the Interrupt Request Register bit to go
from 0 to 1. (In other words, if the interrupt was not already pending at the destination.)
Bit
Description
31:28
Reserved.
27:24
I/O APIC Identification.
This 4 bit field contains the I/O APIC Arbitration ID.
23:0
Reserved.
Bit
Description
63:56
Destination.
If bit 11 of this entry is 0 [Physical], then bits [59:56] specifies an APIC ID. If bit 11 of
this entry is 1 [Logical], then bits [63:56] specify the logical destination address of a set of
processors.
55:17
Reserved.
16
Mask.
0 = Not masked: An edge or level on this interrupt pin results in the delivery of the interrupt to the
destination.
1 =
Masked: Interrupts are not delivered nor held pending. Setting this bit after the interrupt is
accepted by a local APIC has no effect on that interrupt. This behavior is identical to the device
withdrawing the interrupt before it is posted to the processor. It is software's responsibility to
deal with the case where the mask bit is set after the interrupt message has been accepted by
a local APIC unit but before the interrupt is dispensed to the processor.
15
Trigger Mode.
This field indicates the type of signal on the interrupt pin that triggers an interrupt.
0 = Indicates edge sensitive
1 = Indicates level sensitive.