AMD AMD-K6-2/500AFX Data Sheet - Page 231

System Management Mode (SMM), 10.1 Overview, 10.2 SMM Operating Mode and Default Register Values - drivers

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21850J/0-February 2000 Preliminary Information AMD-K6®-2 Processor Data Sheet 10 System Management Mode (SMM) 10.1 10.2 Overview 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 such as power management. These activities appear 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 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 RSM (resume) 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. SMM Operating Mode and Default Register Values The software environment within SMM has the following characteristics: s Addressing and operation in Real mode s 4-Gbyte segment limits s Default 16-bit operand, address, and stack sizes, although instruction prefixes can override these defaults s Control transfers that do not override the default operand size truncate the EIP to 16 bits Chapter 10 System Management Mode (SMM) 211

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Chapter 10
System Management Mode (SMM)
211
21850J/0—February 2000
AMD-K6
®
-2 Processor Data Sheet
Preliminary Information
10
System Management Mode (SMM)
10.1
Overview
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
such as power management. These activities appear
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 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
RSM (resume) 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.
10.2
SMM Operating Mode and Default Register Values
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