PoRegisterSystemState

The PoRegisterSystemState routine registers the system as busy due to certain activity.

PVOID
  PoRegisterSystemState(
    IN PVOID  StateHandle,
    IN EXECUTION_STATE  Flags
    );

Parameters

StateHandle

Pointer to a caller-supplied buffer for a registration state handle. The size, in bytes, of the buffer is sizeof(ULONG). If NULL, this is a new registration. If non-NULL, this parameter points to a handle that was returned by a previous call to PoRegisterSystemState.

Flags

Indicates the type of activity, as specified by a bitwise OR of one or more of the following values:

ES_SYSTEM_REQUIRED

The system is not idle, regardless of apparent load.

ES_DISPLAY_REQUIRED

Use of the display is required.

ES_USER_PRESENT

A user is present.

ES_CONTINUOUS

The settings are continuous and should remain in effect until explicitly changed.

Return Value

PoRegisterSystemState returns a handle to be used later to change or unregister the system busy state. It returns NULL if the handle could not be allocated.

Headers

Declared in wdm.h and ntddk.h. Include wdm.h or ntddk.h.

Comments

PoRegisterSystemState registers the system busy state as indicated by the flags. The registration persists until the caller explicitly changes it with another call to PoRegisterSystemState or cancels it with a call to PoUnregisterSystemState.

The Flags parameter specifies the type of activity in progress. Drivers can specify any combination of the flags.

Setting ES_CONTINUOUS makes the busy state persist until a driver explicitly changes or cancels it by calling PoRegisterSystemState or PoUnregisterSystemState.

A driver can set the system busy state to request that the Power Manager avoid system power state transitions out of the system working state (S0) while driver activity is occurring. Note, however, that under some circumstances (such as a critically low battery) the Power Manager may override this request and put the system to sleep anyway.

Callers of PoRegisterSystemState must be running at IRQL < DISPATCH_LEVEL.

See Also

PoSetSystemState, PoUnregisterSystemState