Intel
®
81341 and 81342—Address Translation Unit (PCI-X)
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
130
Order Number: 315037-002US
2.8
Message-Signaled Interrupts
The Messaging Unit is responsible for the generation of all of the Outbound Interrupts
from the 81341 and 81342. These interrupts can be delivered to the Host Processor via
the
P_INTA#
output pin or the Message Signaled Interrupt (MSI) mechanism.
When a host processor enables Message-Signaled Interrupts (MSI) on the 81341 and
81342, an outbound interrupt is signaled to the host via a PCI write instead of the
assertion of the
P_INTA#
output pin.
In support of MSI, the 81341 and 81342 implements the MSI capability structure. The
capability structure includes the
Section 4.9.30, “MSI Capability Identifier Register -
, the
Section 4.9.31, “MSI Next Item Pointer Register -
, the
Section 4.9.33, “Message Address Register -
Section 4.9.34, “Message Upper Address Register
- Message_Upper_Address” on page 454
and the
Register- Message_Data” on page 455
The Message Unit generates MSIs by writing to the MSI port via the internal bus. The
ATU generates a write transaction whenever the Message Unit writes to the MSI port,
using the address specified in the
Section 4.9.33, “Message Address Register -
Section 4.9.34, “Message Upper Address Register
- Message_Upper_Address” on page 454
and the