User Manual

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2.13.1.1 System States and Power States
Under ACPI, the operating system directs all system and device power state transitions. The
operating system puts devices in and out of low-power states based on user preferences and
knowledge of how devices are being used by applications. Devices that are not being used can be
turned off. The operating system uses information from applications and user settings to put the
system into a low-power state.
Table 5 lists the power states supported by the board along with the associated system power
targets. See the ACPI specification for a complete description of the various system and power
states.
Table 5. System States
State Description
G0/S0/C0 Full On: CPU operating. Individual devices may be shut to save power. The different
CPU operating levels are defined by Cx states.
GO/S0/Cx
Cx State: CPU manages C-states by itself and can be in lower power states.
G1
Suspend-To-RAM (STR): The system context is maintained in system DRAM, but
power is shut to non-critical circuits. Memory is retained and refreshes continue. All
external clocks are shut off; RTC clock and international oscillator clocks are still
toggling.
G1/S4
Suspend-To-Disk (STD): The context of the system is maintained on the disk. All
power is then shut to the system except to the logic required to resume. Externally
appears the same as S5 but may have different wake events.
G2/S5 Soft Off: System context not maintained. All power is shut except for the logic required
to restart. A full boot is required when waking.
G3
Mechanical Off: System context not maintained. All power shut except for the RTC. No
“Wake” events are possible because the system does not have any power. This state
occurs if the user removes the batteries, turns off a mechanical switch, or if the system
power supply is at a level that is insufficient to power the “waking” logic.