Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
9.16.3 User Presence Sensor Events
To communicate changes in user presence to OSPM, AML code should issue a
Notify(upd_device, 0x80) whenever a change in user presence has occurred. The OS
receives this notification and calls the _UPD control method to determine the current user presence
status.
UPD notifications should be generated whenever a transition occurs between one of the user
presence states (absent, present, or unknown) – but at a level of granularity that provides an
appropriate response without overly taxing the system with unnecessary interrupts.
9.17 I/O APIC Device
This optional device describes a discrete I/O APIC device that is not bus enumerated (e.g., as a PCI
device). Describing such a device in the ACPI namespace is only necessary if hot plug of this device
is supported. If hot plug of this device is not supported, an MADT I/O APIC (Section 5.2.12.3,”I/O
APIC Structure”) entry or I/O SAPIC (Section 5.2.12.9, “I/O SAPIC Structure”) entry is sufficient
to describe this device.
An I/O APIC device is an I/O unit that complies with either of the APIC interrupt models supported
by ACPI. These interrupt models are described Section 5.2.12.3,”I/O APIC Structure” and
Section 5.2.12.9,”I/O SAPIC Structure”. If the device is an I/O unit that complies with the APIC
interrupt model, it is declared using the ACPI000A identifier. If this device is an I/O unit that
complies with the SAPIC interrupt model, it is declared using the ACPI000B identifier. If this device
complies with both the APIC and SAPIC interrupt models (I/OxAPIC), it is declared using the
ACPI0009 identifier.
An I/O APIC device declared using any of the above identifiers must contain a _GSB object as
defined inSection 6.2.7, “_GSB (Global System Interrupt Base)” to report its Global System
Interrupt Base. It must also contain a _CRS object that reports the base address of the I/O APIC
device. The _CRS object is required to contain only one resource, a memory resource pointing to the
I/O APIC register base.
Note: Because the _CRS and _GSB methods provide sufficient information, it is not necessary to
provide _MAT under an I/O APIC device.
For an I/O APIC device that is described both in the MADT and in the namespace, the base address
described in the MADT entry must be the same as the base address in the IO APIC device _CRS at
boot time. OSPM must use the information from the MADT until such a time as the _CRS and
_GSB methods in the namespace device can be processed. At this point OSPM must ignore the
MADT entry.
9.18 Time and Alarm Device
The following sections define the operation and definition of the optional control method-based
Time and Alarm device, which provides a hardware independent abstraction and a more robust
alternative to the Real Time Clock (RTC), See Section 9.15, "PC/AT RTC/CMOS Devices".
The time capabilities of the time and alarm device maintain the time of day information across
platform power transitions, and keep track of time even when the platform is turned off. It is
538 April, 2015 Version 6.0