Intel ARCHITECTURE IA-32 User Manual download pdf (Page 376)

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9-2 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

The software-initialization code performs all system-specific initialization of the BSP or

primary processor and the system logic.

At this point, for MP (or DP) systems, the BSP (or primary) processor wakes up each AP (or

secondary) processor to enable those processors to execute self-configuration code.

When all processors are initialized, configured, and synchronized, the BSP or primary processor

begins executing an initial operating-system or executive task.

The x87 FPU is also initialized to a known state during hardware reset. x87 FPU software initial-

ization code can then be executed to perform operations such as setting the precision of the x87

FPU and the exception masks. No special initialization of the x87 FPU is required to switch

operating modes.

Asserting the INIT# pin on the processor invokes a similar response to a hardware reset. The

major difference is that during an INIT, the internal caches, MSRs, MTRRs, and x87 FPU state

are left unchanged (although, the TLBs and BTB are invalidated as with a hardware reset). An

INIT provides a method for switching from protected to real-address mode while maintaining

the contents of the internal caches.

9.1.1 Processor State After Reset

Table 9-1 shows the state of the flags and other registers following power-up for the Pentium 4,

Intel Xeon, P6 family, and Pentium processors. The state of control register CR0 is 60000010H

(see Figure 9-1). This places the processor is in real-address mode with paging disabled.

9.1.2 Processor Built-In Self-Test (BIST)

Hardware may request that the BIST be performed at power-up. The EAX register is cleared

(0H) if the processor passes the BIST. A nonzero value in the EAX register after the BIST indi-

cates that a processor fault was detected. If the BIST is not requested, the contents of the EAX

The overhead for performing a BIST varies between processor families. For example, the BIST

takes approximately 30 million processor clock periods to execute on the Pentium 4 processor.

(This clock count is model-specific, and Intel reserves the right to change the exact number of

periods, for any of the IA-32 processors, without notification.)

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