The Interrupt Message Address Range


The reserved address range used by the Interrupt Request and EOI messages is pictured in Figure 8-2 on page 202. This 3984MB address range is mapped from location FD_0000_0000h to FD_F8FF_FFFFh.

Figure 8-2. Interrupt Request and EOI Message Reserved Address Range

graphics/08fig02.jpg

The specified range reserved for the interrupt request packets seems straight forward until one looks at the interrupt request packet definition (Figure 8-2 on page 202). Note that the address field (byte 7) defined by the specification includes only Addr[39:32]. These upper eight address bits identify a 4GB address range starting at FD_0000_0000h. When reviewing the address map in Figure 8-2, it can be seen that several reserved address blocks fall within this 4GB address range ” from Legacy PCI Ack through Configuration.

Figure 8-3 on page 203 depicts the format of the Interrupt Request packet. Note that the specification defines only Addr[39-32] to identify the interrupt packet address. If the interrupt request and EOI packets were limited to Addr[39:32], the host could not differentiate the interrupt packets from packets associated with other address ranges and functions.

Figure 8-3. Interrupt Request Packet Address Field

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The address associated with the interrupt packets must include additional address bits to distinguish between the difference address ranges. If the Host Bridge is to resolve the address to within the specified interrupt address range (FD_0000_0000h to FD_F8FF_FFFFh), then Addr[31:24] must be included within the interrupt packets. Verification of the specification's intent can be found in the x86 compatibility definitions, which specify Addr[31:24] be delivered in the IntrInfo[31:24] field of the interrupt packet. To maintain compatibility with earlier versions of HT implementations , the specification sets a default value of F8h for IntrInfo[31:24].

For system platform implementations other than x86, the specification leaves open the possibility of the interrupt range being extended, but does not explicitly state that the interrupt range can be extended in the absence of the PIC IACK, System Management, and IO mappings. For example, some platforms may only need support for the interrupt and configuration packets. This would require the use of Addr[39:26], thereby permitting the Host Bridge to distinguish between the interrupt and configuration requests .



HyperTransport System Architecture
HyperTransportв„ў System Architecture
ISBN: 0321168453
EAN: 2147483647
Year: 2003
Pages: 182

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