Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
Table 9-265 User Presence Detection Device
Object
_UPD
_UPP
Description
The current user presence detection reading. [Required]
User presence detection polling frequency in tenths of seconds. [Optional]
9.16.1 _UPD (User Presence Detect)
This control method returns the user presence detection reading, indicating whether or not the user is
currently present from the perspective of this sensor. Three states are currently defined for UPD
sensor readings: absent, present, and unknown, represented by the values 0x00, 0x01, and 0xFF
respectively. The unknown state is used to convey that the sensor is currently unable to determine
user presence due to some environmental or other transient factor. All other values are reserved.
Arguments:
None
Return Value:
An Integer containing the user presence code:
0x00 –Absent: A user is not currently detected by this sensor.
0x01 –Present: A user is currently detected by this sensor.
0xFF –Unknown: The sensor is currently unable to determine if a user is present or absent.
9.16.2 _UPP (User Presence Polling)
This optional object evaluates to a recommended polling frequency (in tenths of seconds) for this
user presence sensor. A value of zero – or the absence of this object when other UPD objects are
defined – indicates that the OS does not need to poll the sensor in order to detect meaningful changes
in user presence (the hardware is capable of generating asynchronous notifications).
Arguments:
None
Return Value:
An Integer containing the recommended polling frequency in tenths of seconds. A value of zero
indicates that polling is not required.
The use of polling is allowed but strongly discouraged by this specification. OEMs should design
systems that asynchronously notify OSPM whenever a meaningful change in user presence occurs—
relieving the OS of the overhead associated with polling.
This value is specified as tenths of seconds. For example, a value of 10 would be used to indicate a 1
second polling frequency. As this is a recommended value, OSPM will consider other factors when
determining the actual polling frequency to use.
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