Intel IA-32 - Manual (Page 286)

7-18 Vol. 3A
MULTIPLE-PROCESSOR MANAGEMENT
• The remainder of the processors (which were not selected as the BSP) are
designated as APs. They leave their BSP flags in the clear state and enter a “wait-
for-SIPI state.”
• The newly established BSP broadcasts an FIPI message to “all including self,”
which the BSP and APs treat as an end of MP initialization signal. Only the
processor with its BSP flag set responds to the FIPI message. It responds by
fetching and executing the BIOS boot-strap code, beginning at the reset vector
(physical address FFFF FFF0H).
5. As part of the boot-strap code, the BSP creates an ACPI table and an MP table and adds its
initial APIC ID to these tables as appropriate.
6. At the end of the boot-strap procedure, the BSP sets a processor counter to 1, then
broadcasts a SIPI message to all the APs in the system. Here, the SIPI message contains a
vector to the BIOS AP initialization code (at 000VV000H, where VV is the vector
contained in the SIPI message).
7. The first action of the AP initialization code is to set up a race (among the APs) to a BIOS
initialization semaphore. The first AP to the semaphore begins executing the initialization
code. (See Section 7.5.4, “MP Initialization Example,” for semaphore implementation
details.) As part of the AP initialization procedure, the AP adds its APIC ID number to the
ACPI and MP tables as appropriate and increments the processor counter by 1. At the
completion of the initialization procedure, the AP executes a CLI instruction and halts
itself.
8. When each of the APs has gained access to the semaphore and executed the AP initial-
ization code, the BSP establishes a count for the number of processors connected to the
system bus, completes executing the BIOS boot-strap code, and then begins executing
operating-system boot-strap and start-up code.
9. While the BSP is executing operating-system boot-strap and start-up code, the APs remain
in the halted state. In this state they will respond only to INITs, NMIs, and SMIs. They will
also respond to snoops and to assertions of the STPCLK# pin.
The following section gives an example (with code) of the MP initialization protocol for
multiple Intel Xeon processors operating in an MP configuration.
Appendix B, “Model-Specific Registers (MSRs),” describes how to program the LINT[0:1] pins
of the processor’s local APICs after an MP configuration has been completed.
7.5.4 MP Initialization Example
The following example illustrates the use of the MP initialization protocol to initialize IA-32
processors in an MP system after the BSP and APs have been established. This code runs on
IA-32 processors that use MP initialization protocol. This includes P6 Family processors,
Pentium 4 processors and Intel Xeon processors (with or without Intel
®
Hyper-Threading Tech-
nology support).