Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
PSCI_USE_HVC 1 1 1 if HVC must be used as the PSCI conduit.instead of SMC.
Reserved 14 2 This value is zero.
5.2.10 Firmware ACPI Control Structure (FACS)
The Firmware ACPI Control Structure (FACS) is a structure in read/write memory that the BIOS
reserves for ACPI usage. This structure is optional if and only if the
HARDWARE_REDUCED_ACPI flag in the FADT is set. The FACS is passed to an ACPIcompatible
OS using the FADT. For more information about the FADT FIRMWARE_CTRL field,
see Table 5.2.9, “Fixed ACPI Description Table (FADT).”
The BIOS aligns the FACS on a 64-byte boundary anywhere within the system’s memory address
space. The memory where the FACS structure resides must not be reported as system
AddressRangeMemory in the system address map. For example, the E820 address map reporting
interface would report the region as AddressRangeReserved. For more information about system
address map reporting interfaces, see Section 15, “System Address Map Interfaces.”
Table 5-38 Firmware ACPI Control Structure (FACS)
Field
Byte
Length
Byte
Offset Description
Signature 4 0 ‘FACS’
Length 4 4 Length, in bytes, of the entire Firmware ACPI Control Structure.
This value is 64 bytes or larger.
Hardware Signature 4 8 The value of the system's "hardware signature" at last boot.
This value is calculated by the BIOS on a best effort basis to
indicate the base hardware configuration of the system such
that different base hardware configurations can have different
hardware signature values. Although memory described using
or EfiPersistentMemory (Section 15) iis not saved/restored by
OS during S4, any change to persistent memory that impacts
any OS visible firmware interfaces must change hardware
signature. Any change to the data in Persistent Memory itself
should not be included in computing the hardware signature.
OSPM uses this information in waking from an S4 state, by
comparing the current hardware signature to the signature
values saved in the non-volatile sleep image. If the values are
not the same, OSPM assumes that the saved non-volatile
image is from a different hardware configuration and cannot be
restored.
130 April, 2015 Version 6.0