Advanced Configuration and Power Interface Specification

ACPI Software Programming Model
Table 5-39 Firmware Control Structure Feature Flags
FACS – Flag
Bit
Length
Bit
Offset
Description
S4BIOS_F 1 0 Indicates whether the platform supports S4BIOS_REQ. If
S4BIOS_REQ is not supported, OSPM must be able to save
and restore the memory state in order to use the S4 state.
64BIT_WAKE_SUPP
ORTED_F
1 1 Indicates that the platform firmware supports a 64 bit execution
environment for the waking vector. When set and the OSPM
additionally set 64BIT_WAKE_F, the platform firmware will
create a 64 bit execution environment before transferring
control to the X_Firmware_Waking_Vector.
Reserved 30 2 The value is zero.
Table 5-40 OSPM Enabled Firmware Control Structure Feature Flags
FACS – Flag
Bit
Length
Bit
Offset
Description
64BIT_WAKE_F 1 0 OSPM sets this bit to indicate to platform firmware that the
X_Firmware_Waking_Vector requires a 64 bit execution
environment.
This flag can only be set if platform firmware sets
64BIT_WAKE_SUPPORTED_F in the FACS flags field.
This bit field has no affect on Itanium TM Processor Family
(IPF) -based platforms, which require a 64 bit execution
environment.
Reserved 31 1 The value is zero.
5.2.10.1 Global Lock
The purpose of the ACPI Global Lock is to provide mutual exclusion between the host OS and the
ROM BIOS. The Global Lock is a 32-bit (DWORD) value in read/write memory located within the
FACS and is accessed and updated by both the OS environment and the SMI environment in a
defined manner to provide an exclusive lock. Note: this is not a pointer to the Global Lock, it is the
actual memory location of the lock. The FACS and Global Lock may be located anywhere in
physical memory.
By convention, this lock is used to ensure that while one environment is accessing some hardware,
the other environment is not. By this convention, when ownership of the lock fails because the other
environment owns it, the requesting environment sets a “pending” state within the lock, exits its
attempt to acquire the lock, and waits for the owning environment to signal that the lock has been
released before attempting to acquire the lock again. When releasing the lock, if the pending bit in
the lock is set after the lock is released, a signal is sent via an interrupt mechanism to the other
environment to inform it that the lock has been released. During interrupt handling for the “lock
released” event within the corresponding environment, if the lock ownership were still desired an
attempt to acquire the lock would be made. If ownership is not acquired, then the environment must
again set “pending” and wait for another “lock release” signal.
The table below shows the encoding of the Global Lock DWORD in memory.
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