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Processor Programming (Continued)

3.7

SYSTEM MANAGEMENT MODE

System Management Mode (SMM) is an enhancement of

the standard x86 architecture. SMM is usually employed for

system power management or software-transparent emula-

tion of I/O peripherals. SMM is entered through a hardware

signal “System Management Interrupt” (SMI# pin) that has

a higher priority than any other interrupt, including NMI. An

SMM interrupt can also be triggered from software using

an SMINT instruction. Following an SMM interrupt, portions

of the CPU state are automatically saved, SMM is entered,

and program execution begins at the base of SMM address

space (Figure 3-9).

The GX1 processor extends System Management Mode to

support the virtualization of many devices, including VGA

video. The SMM mechanism can be triggered by I/O activ-

ity and also by access to selected memory regions. For

example, SMM interrupts are generated when VGA

addresses are accessed. As will be described, other SMM

enhancements have reduced SMM overhead and improved

virtualization-software performance

Figure 3-9. System Management Memory Address Space

FFFFFFFFh

00000000h

Non-SMM

SMM

Potential

SMM Address

Space

Physical

Memory Space

FFFFFFFFh

00000000h

4KB to 32MB

Physical Memory

4GB

Defined

SMM

Address

Space

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