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
emulation 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 automati-
cally saved, SMM is entered, and program execution
begins at the base of SMM address space (Figure 3-9).
The GXLV processor extends System Management Mode
to support the virtualization of many devices, including
VGA video. The SMM mechanism can be triggered not
only by I/O activity, but 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
Potential
Physical
Memory Space
SMM Address
Space
FFFFFFFFh
FFFFFFFFh
Defined
SMM
Address
Space
Physical Memory
4 GB
4 KB to 32 MB
00000000h
Non-SMM
00000000h
SMM
Figure 3-9. System Management Memory Address Space
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