Arbitration Cycles; Apic Message Formats - Intel 6300ESB Datasheet

When the Intel
an interrupt to send over the APIC bus, it drives a start cycle to begin arbitration, by
driving bit 0 to a '0' on an APICCLK rising edge. It then samples bit 1. When Bit 1 was a
zero, then a local APIC started arbitration for an EOI message on the same clock edge
that the Intel
arbitration and will stop driving the APIC bus.
When the Intel
transferring its arbitration ID, located in bits [27:24] of its Arbitration ID register
(ARBID). Starting in Cycle 2, through Cycle 5, it will tri-state bit 0, and drive bit 1 to a
'0' when ARBID[27] is a '1'. When ARBID[27] is a '0', it will also tri-state bit 1. At the
end of each cycle, the Intel
bus. When the Intel
samples a '0', then another APIC agent started arbitration for the APIC bus at the same
time as the Intel
will stop driving the APIC bus.
Table 47.

Arbitration Cycles

Cycle
1
2
3
4
5
5.7.5.2 Bus Message Formats
After bus arbitration, the winner is granted exclusive use of the bus and will drive its
message. APIC messages come in four formats, determined by the Delivery Mode bits.
These four messages are of different length, and are known by all APICs on the bus
through the transmission of the Delivery Mode bits:
Table 48.

APIC Message Formats

Message
EOI
Short
Lowest
Priority
Remote Read
EOI Message for Level Triggered Interrupts
EOI messages are used by local APICs to send an EOI cycle occurring for a level
triggered interrupt to an I/O APIC. This message is needed so that the I/O APIC may
differentiate between a new interrupt on the interrupt line versus the same interrupt on
the interrupt line. The target of the EOI is given by the local APIC through the
transmission of the priority vector (V7 through V0) of the interrupt. Upon receiving this
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Intel 6300ESB I/O Controller Hub
DS
126
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6300ESB ICH detects a bus idle condition on the APIC Bus, and it has
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6300ESB ICH started arbitration. The Intel
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6300ESB ICH did not see an EOI message start, it will start
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6300ESB ICH will sample the state of Bit 1 on the APIC
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6300ESB ICH did not drive Bit 1 (ARBID[27] = '0'), and it
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6300ESB ICH, and it has higher priority. The Intel
Table 47
Bit 1 Bit 0
EOI 0
NOT (ARBID[27]) 1
NOT (ARBID[26]) 1
NOT (ARBID[25]) 1
NOT (ARBID[24]) 1
# of Delivery
Cycles Mode Bits
14 xxx
001, 010, 100,
21
101, 111
33 001
39 011
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6300ESB ICH has thus lost
describes the arbitration cycles.
Comment
Bit 1 = 1: Normal, Bit 1 = 0: EOI
Arbitration ID. When the Intel
a different value than it sent, it lost arbitration.
Comments
End of Interrupt transmission from Local APIC to I/O
APIC on Level interrupts. EOI is known by the EOI
bit at the start of arbitration
I/O APIC delivery on Fixed, NMI, SMI, Reset, ExtINT,
and Lowest Priority with focus processor messages
Transmission of Lowest Priority interrupts when the
status field indicates that the processor does not
have focus.
Message from one Local APIC to another to read
registers.
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Intel 6300ESB ICH—5
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6300ESB ICH
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6300ESB ICH samples
November 2007
Order Number: 300641-004US