AMD-K6-2E/400AFR AMD [Advanced Micro Devices], AMD-K6-2E/400AFR Datasheet - Page 235

• Manufacturer Part Number: AMD-K6-2E/400AFR
• Manufacturer: AMD [Advanced Micro Devices]

22529B/0—January 2000
11
11.1
Chapter 11
System Management Mode (SMM)
SMM Operating Mode and Default Register Values
SMM is an alternate operating mode entered by way of a system
management interrupt (SMI) and handled by an interrupt
service routine. SMM is designed for system control activities
s u ch a s p owe r m a n a g e m e n t . Th e s e a c t iv i t i e s a p p e a r
transparent to conventional operating systems like DOS and
Windows. SMM is primarily targeted for use by the Basic Input
Output System (BIOS) and specialized low-level device drivers.
The code and data for SMM are stored in the SMM memory
area, which is isolated from main memory.
The processor enters SMM by the system logic’s assertion of the
SMI# interrupt and the processor’s acknowledgment by the
assertion of SMIACT#. At this point the processor saves its state
into the SMM memory state-save area and jumps to the SMM
service routine. The processor returns from SMM when it
executes the resume (RSM) instruction from within the SMM
service routine. Subsequently, the processor restores its state
from the SMM save area, negates SMIACT#, and resumes
execution with the instruction following the point where it
entered SMM.
The following sections summarize the SMM state-save area,
entry into and exit from SMM, exceptions and interrupts in
SMM, memory allocation and addressing in SMM, and the SMI#
and SMIACT# signals.
The software environment within SMM has the following
characteristics:
Addressing and operation in real mode
4-Gbyte segment limits
Default 16-bit operand, address, and stack sizes, although
instruction prefixes can override these defaults
Control transfers that do not override the default operand
size truncate the EIP to 16 bits
Far jumps or calls cannot transfer control to a segment with
a base address requiring more than 20 bits, as in real mode
segment-base addressing
System Management Mode (SMM)
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