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Any driver can register an IoTimer routine, after it creates one or more device objects, by calling IoInitializeTimer. The driver can then start the timer by calling IoStartTimer. The following figure illustrates these calls.
After calling IoCreateDevice to create device objects, a driver can call IoInitializeTimer with the entry point of its IoTimer routine, along with pointers to a driver-created device object and a context area in which the driver maintains whatever context its IoTimer routine uses. The I/O manager associates the device object with a kernel-allocated timer object and sets up the timer object to time out every second.
After the driver calls IoStartTimer, its IoTimer routine is called once per second until the driver calls IoStopTimer. A driver can reenable calls to its IoTimer routine with IoStartTimer. (Frequently, when a driver calls IoStartTimer, it supplies the device object pointer obtained from the I/O stack location of the current IRP.)
On entry, the IoTimer routine is passed the device object pointer, along with the context pointer that the driver supplied when it called IoInitializeTimer.
Drivers must not call IoStopTimer from within an IoTimer routine.
The I/O manager unregisters the timer routine for a specified device object and frees its associated context when the driver calls IoDeleteDevice.