Intel
82801BA ICH2 Datasheet
5-57
Functional Description
DT bit in the Boot Configuration Register
This enables the ICH2 to deliver interrupts as memory writes. This bit is ignored if the APIC mode
is not enabled.
5.8.5.5
Interrupt Message Format
ICH2 writes the message to PCI (and to the Host Controller) as a 32-bit memory write cycle. It uses
the formats shown in
Table 5-27
and
Table 5-28
for the address and data.
:
Table 5-27. Interrupt Message Address Format
Bit
Description
31:20
Will always be FEEh
19:12
Destination ID:
This is the same as bits 63:56 of the I/O Redirection Table entry for the interrupt
associated with this message.
11:4
Reserved (will always be 0)
3
Redirection Hint:
This bit is used by the processor host bridge to allow the interrupt message to be
redirected.
0 = The message will be delivered to the agent (processor) listed in bits 19:4.
1 = The message will be delivered to an agent with a lower interrupt priority This can be derived from
bits 10:8 in the Data Field (see below).
The Redirection Hint bit = 1 if bits 10:8 in the Delivery Mode field associated with corresponding
interrupt are encoded as 001 (Lowest Priority). Otherwise, the Redirection Hint bit = 0.
2
Destination Mode:
This bit is used only the Redirection Hint bit = 1. If the Redirection Hint bit and
the Destination Mode bit are both set to 1, the logical destination mode is used and the redirection is
limited only to those processors that are part of the logical group as based on the logical ID.
1:0
Will always be 00.
Table 5-28. Interrupt Message Data Format
Bit
Description
31:16
Will always be 0000h.
15
Trigger Mode:
1 = Level, 0 = Edge. Same as the corresponding bit in the I/O Redirection Table for
that interrupt.
14
Delivery Status:
1 = Assert, 0 = Deassert.
If using edge-triggered interrupts, then this bit will always be 1, since only the assertion is sent.
If using level-triggered interrupts, then this bit indicates the state of the interrupt input.
13:12
Will always be 00
11
Destination Mode:
1 = Logical. 0 = Physical. Same as the corresponding bit in the I/O Redirection
Table for that interrupt.
10:8
Delivery Mode:
This is the same as the corresponding bits in the I/O Redirection Table for that
interrupt.
000 = Fixed 100 = NMI
001 = Lowest Priority 101 = INIT
010 = SMI/PMI 110 = Reserved
011 = Reserved 111 = ExtINT
7:0
Vector:
This is the same as the corresponding bits in the I/O Redirection Table for that interrupt.
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