Microsoft Windows Embedded CE 6.0 Exam Preparation Kit

Value	A (10 minutes)	0x20
Description	The Timeout registry entry defines the timer threshold in minutes.	The WakeSources registry entry is optional and defines a list of identifiers for possible wake sources. During device-initiated wakeup, Power Manager uses the IOCTL_HAL_GET_WAKE_SOURCE input and output control (IOCTL) code to determine the wake source and sets associated activity timers to active.

NOTE

Activity timers

Defining activity timers causes the Power Manager to construct a set of named events for resetting the timer and for obtaining activity status. For more information, see the section 'Activity Timers' in the Windows Embedded CE 6.0 Documentation available on the Microsoft MSDN website at http://msdn2.microsoft.com/en-us/library/aa923909.aspx.

Power Management API

As mentioned earlier in this lesson, Power Manager exposes three interfaces to enable applications and drives for power management: notification interface, driver interface, and application interface.

Notification Interface

The notification interface provides two functions that applications can use to register and deregister for power notifications through message queues, as listed in Table 3-17. It is important to note that power notifications are multicast messages, which means that Power Manager sends these notification messages only to registered processes. In this way, power management-enabled applications can seamlessly coexist on Windows Embedded CE with applications that do not implement the Power Management API.

Table 3-17 Power Management notification interface

Function	Description
RequestPowerNotifications	Registers an application process with Power Manager to receive power notifications. Power Manager then sends the following notification messages:
	¦ PBT_RESUME The system resumes from Suspend state.
	¦ PBT_POWERSTATUSCHANGE The system transitions between AC power and battery power.
	¦ PBT_TRANSITION The system changes to a new power state.
	¦ PBT_POWERINFOCHANGE The battery status changes. This message is only valid if a battery driver is loaded.
StopPowerNotifications	Unregisters an application process so it no longer receives power notifications.

The following sample code illustrates how to use power notifications:

// Size of a POWER_BROADCAST message.
DWORD cbPowerMsgSize =
 sizeof POWER_BROADCAST + (MAX_PATH * sizeof TCHAR);
// Initialize a MSGQUEUEOPTIONS structure.
MSGQUEUEOPTIONS mqo;
mqo.dwSize = sizeof(MSGQUEUEOPTIONS);
mqo.dwFlags = MSGQUEUE_NOPRECOMMIT;
mqo.dwMaxMessages = 4;
mqo.cbMaxMessage = cbPowerMsgSize;
mqo.bReadAccess = TRUE;
//Create a message queue to receive power notifications.
HANDLE hPowerMsgQ = CreateMsgQueue(NULL, &mqo);
if (NULL == hPowerMsgQ) {
 RETAILMSG(1, (L'CreateMsgQueue failed: %x
', GetLastError()));
 return ERROR;
}
// Request power notifications.
HANDLE hPowerNotifications = RequestPowerNotifications(hPowerMsgQ,
 PBT_TRANSITION | PBT_RESUME | PBT_POWERINFOCHANGE);