Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
the power source is not consistent with the timer type. The expired timer policy is applied in
conjunction with expired timer persistence described earlier.
For example, if a mobile platform programs the AC timer to be 2 hours long and DC timer to be 4
hours long and then transitions from the S0 state to S3 state at 1:00 AM, the AC timer is set to expire
at 3:00 AM and the DC timer is set to expire at 5:00 AM. For the AC Timer, a expired timer wake
policy value is programmed as 60 seconds.
If the platform is unplugged from AC power at 1:40 AM and remains unplugged, the Time and
Alarm Device will not wake up the system at 3:00 AM. If the platform remains on DC power until
5:00 AM when the DC timer expires, a wake signal will then be asserted. The following graph
illustrates the above example.
Go to S3 AC timer expires DC timer expires
2 hours
S0
S3
AC
DC
1:00 AM 1:40 AM 3:00 AM 5:00 AM
Time
4 hours
Figure 9-56 System transitions with WakeAlarm -- Timer
If the AC power is plugged in again at 4:00 AM, then the system will be woken up at 4:01 AM due
to the AC expired timer wake policy value setting. The following graph illustrates this.
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