Suspend and Resume Power Callbacks
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4/8/2010
Suspend and resume power callbacks are independent of Power Manager. These callbacks occur when the system is about to enter a suspend state in which the CPU is stopped.
** Device drivers often receive Power Manager I/O control calls before the system Suspend state that request the driver to turn itself off. This is not always the case, however. Power Manager enables devices to be turned off while the system is running or left on while the system is suspended.
You can decide what action to take if a power-down callback is received while the device power state is D0, D1, or D2. You can often resolve this by turning the device off, and then back on again when the power-up callback occurs. However, if the device can function without the CPU, it may be appropriate for you to leave the device turned on. If your device is left in a powered state while in the system Suspend state, this might indicate that Power Manager is configured incorrectly, or an application may have called SetPowerRequirement on your device with the POWER_FORCE flag set.