82870P2P64H2 Datasheet, PDF (104/217 Pages) –

Register Description
R
3.4.3.2
3.4.3.3
VS—Version Register (D28,30: F0)
Offset:
01h
Default Value: 00178020h
Attribute:
Size:
RO
32 bits
This register contains information related to this I/OxAPIC for driver / OS software.
Bits
Description
31:24
23:16
15
14:8
7:0
Reserved
Maximum Redirection Entries (MAX). This is the entry number of the highest entry in the
redirection table. It is equal to the number of interrupt inputs minus one. This field is hardwired to
17h to indicate 24 interrupts. (Default=17h)
IRQ Assertion Register Supported (PRQ). This bit is set to 1 to indicate that this version of the
I/OxAPIC implements the IRQ Assertion register and allows PCI devices to write to it to cause
interrupts. (Default=01h)
Reserved
Version (VS). This identifies the implementation version. This field is hardwired to 20h to indicate
this is an I/OxAPIC. (Default=20h)
ARBID—Arbitration ID Register (D28,30: F0)
Offset:
02h
Default Value: 00000000h
Attribute:
Size:
RO
32 bits
This register contains the bus arbitration priority for the APIC, and is loaded when 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. All other agents,
except the agent whose arbitration ID is Fh, increment their arbitration IDs by one. The agent
whose ID was 15 takes the winner’s arbitration ID and increments it by one.
Arbitration IDs are changed only for messages that are transmitted successfully, except in the case
of Low Priority messages, where the arbitration ID is changed even if the message was not
successfully transmitted. A message is transmitted successfully if no checksum error or acceptance
error was reported for that message. The APIC Arbitration ID register is always loaded with APIC
ID during a "level triggered INIT with deassert" message.
Bits
Description
31:28
27:24
23:0
Reserved
Arbitration ID (ARBID). This 4-bit field contains the I/OxAPIC Arbitration ID.
Reserved
104
Intel^® 82870P2 P64H2 Datasheet