Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
initial TMR_VAL upon loading OSPM and assumes that the timer is counting. It is allowable to stop
the Timer when the system transitions out of the working (G0/S0) state. The only timer reset
requirement is that the timer functions while in the working state.
The PM Timer’s programming model is implemented as a fixed hardware feature to increase the
accuracy of reading the timer.
4.8.2.2 Console Buttons
ACPI defines user-initiated events to request OSPM to transition the platform between the G0
working state and the G1 sleeping, G2 soft off and G3 mechanical off states. ACPI also defines a
recommended mechanism to unconditionally transition the platform from a hung G0 working state
to the G2 soft-off state.
ACPI operating systems use power button events to determine when the user is present. As such,
these ACPI events are associated with buttons in the ACPI specification.
The ACPI specification supports two button models:
• A single-button model that generates an event for both sleeping and entering the soft-off state.
The function of the button can be configured using OSPM UI.
• A dual-button model where the power button generates a soft-off transition request and a
sleeping button generates a sleeping transition request. The type of button implies the function
of the button.
Control of these button events is either through the fixed hardware programming model or the
generic hardware programming model (control method based). The fixed hardware programming
model has the advantage that OSPM can access the button at any time, including when the system is
crashed. In a crashed system with a fixed hardware power button, OSPM can make a “best” effort to
determine whether the power button has been pressed to transition to the system to the soft-off state,
because it doesn’t require the AML interpreter to access the event bits.
4.8.2.2.1 Power Button
The power button logic can be used in one of two models: single button or dual button. In the singlebutton
model, the user button acts as both a power button for transitioning the system between the
G0 and G2 states and a sleeping button for transitioning the system between the G0 and G1 states.
The action of the user pressing the button is determined by software policy or user settings. In the
dual-button model, there are separate buttons for sleeping and power control. Although the buttons
still generate events that cause software to take an action, the function of the button is now
dedicated: the sleeping button generates a sleeping request to OSPM and the power button generates
a waking request.
Support for a power button is indicated by a combination of the PWR_BUTTON flag and the power
button device object, as shown in the following:
Table 4-13 Power Button Support
Indicated Support PWR_BUTTON Flag Power Button Device Object
Fixed hardware power button Clear Absent
Control method power button Set Present
76 April, 2015 Version 6.0