Intel 64 and IA-32 Architectures Software Developers Manual Volume 3B, System Programming Guide Part 2

Table Of Contents
F-2 Vol. 3
APIC BUS MESSAGE FORMATS
The checksum is computed for cycles 6 through 9. It is a cumulative sum of the 2-bit
(Bit1:Bit0) logical data values. The carry out of all but the last addition is added to
the sum. If any APIC computes a different checksum than the one appearing on the
bus in cycle 10, it signals an error, driving 11 on the APIC bus during cycle 12. In this
case, the APICs disregard the message. The sending APIC will receive an appropriate
error indication (see Section 9.6.3, “Error Handling”) and resend the message. The
status cycles are defined in Table F-4.
F.2.1 Short Message
Short messages (21-cycles) are used for sending fixed, NMI, SMI, INIT, start-up,
ExtINT and lowest-priority-with-focus interrupts. Table F-2 shows the cycles in a
short message.
Table F-2. Short Message (21 Cycles)
Cycle Bit1 Bit0
1010 1 = normal
2 ArbID3 0 Arbitration ID bits 3 through 0
3ArbID20
4ArbID10
5ArbID00
6 DM M2 DM = Destination Mode
7M1M0M2-M0 = Delivery mode
8 L TM L = Level, TM = Trigger Mode
9 V7 V6 V7-V0 = Interrupt Vector
10 V5 V4
11 V3 V2
12 V1 V0
13 D7 D6 D7-D0 = Destination
14 D5 D4
15 D3 D2
16 D1 D0
17 C C Checksum for cycles 6-16
18 0 0
19 A A Status cycle 0
20 A1 A1 Status cycle 1
21 0 0 Idle