enum DEVICE_POWER_STATE

typedef enum _DEVICE_POWER_STATE
{
         PowerDeviceUnspecified = 0,
         PowerDeviceD0 = 1,
         PowerDeviceD1 = 2,
         PowerDeviceD2 = 3,
         PowerDeviceD3 = 4,
         PowerDeviceMaximum = 5
} DEVICE_POWER_STATE;

Windows Vista Kernel Structures