Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
Figure 9-52 System transitions with WakeAlarm -- Policy
The Time and Alarm device can support a range of services, the OSPM evaluates the _GCP object to
get the supported capabilities of the device. If the capabilities indicate that the device supports time
services, the OSPM evaluates the _GRT and _SRT objects to get and set time respectively.
If alarm services are supported by the device, the OSPM evaluates the _STV object to program both
the AC and DC timer values. The values, which are in units of seconds, indicate the elapsed time
before the timer expires. OSPM evaluates the _TIV object to read the current AC and DC timer
values (seconds remaining until expiration).
OSPM evaluates the _STP object to set timer policies for both the AC and DC timers OSPM reads
the current timer policy by evaluating the _TIP object, which return policy settings for both the AC
and DC timer.
The OSPM evaluates the _GWS object to identify expired timers that may have waked the platform.
The OSPM must evaluate the _CWS object to clear any expired timer events that can prevent the
system from performing a sleep transition according the expired timer wake policy, and the expired
timer persistence described above.
The Time and Alarm device, if implemented with wake support, must support waking up the system
from S3. Waking from S4/S5 support is optional. If the Time and Alarm device support AC/DC
wake, Wake support for any power state must be made available on both AC and DC power sources.
9.18.2 _GCP (Get Capability)
S0
S3
AC
DC
Go to S3 AC timer expires DC timer expires
2 hours
4 hours
4:00 AM
1:00 AM 1:40 AM 3:00 AM 5:00 AM
This object is required and provides the OSPM with a bit mask of the device capabilities. The device
can implement the time function in addition to the wake function. The capabilities bitmask will
indicate to the OSPM what support is implemented. If the platform implements both AC and DC
timers then it is capable of waking up based on the power source
478 Hewlett-Packard/Intel/Microsoft/Phoenix/Toshiba
Time