Processor Programming (Continued)
3.11 SYSTEM MANAGEMENT MODE
System Management Mode (SMM) is usually employed
for system power management or software-transparent
emulation of I/O peripherals. SMM mode is entered
through a hardware signal “System Management Inter-
rupt” (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. Fol-
lowing an SMM interrupt, portions of the CPU state are
automatically saved, SMM mode is entered, and program
execution begins at the base of SMM address space (Fig-
ure 3-9).
The GXm processor extends System Management Mode
(SMM) to support the virtualization of many devices,
including VGA video. The SMM mechanism can be trig-
gered not only by I/O activity, but by access to selected
memory regions. For example, SMM interrupts are gener-
ated when VGA addresses are accessed. As will be
described, other SMM enhancements have reduced SMM
overhead and improved virtualization-software perfor-
mance
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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