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Connecting an Interrupt Service Routine to a Parallel Port

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A kernel-mode client can use a IOCTL_INTERNAL_PARALLEL_CONNECT_INTERRUPT request to connect an interrupt service routine and a deferred port check routine to the operation of the parallel port function driver.

Note   Microsoft does not recommend using a client-supplied interrupt routine. The use of interrupts might cause system instability. By default, the IOCTL_INTERNAL_PARALLEL_CONNECT_INTERRUPT request is disabled.

To facilitate the porting and development of drivers for parallel devices, the system-supplied function driver for parallel ports supports a registry flag that kernel-mode clients can use to enable and disable a connect interrupt request. The connect interrupt request is enabled by the registry entry value EnableConnectInterruptIoctl under the Plug and Play registry key for the parallel port. The entry value has type REG_DWORD and the default value is 0x0 (disabled). A value that is not equal to 0x0 enables the connect interrupt request.

The connect interrupt request returns a PARALLEL_INTERRUPT_INFORMATION structure that includes a pointer to the parallel port's interrupt object and the following pointers to system-supplied callback routines:

  • The TryAllocatePortAtInterruptLevel member is a pointer to a nonblocking PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback, which a kernel-mode driver can use in an ISR to allocate a parallel port.

  • The FreePortFromInterruptLevel member is a pointer to a nonblocking PPARALLEL_FREE_ROUTINE (ISR) callback that a kernel-mode driver can use in an ISR to free a parallel port.

The interrupt service routine is called at IRQL = DIRQL after a hardware interrupt on the parallel port. If a driver connects an interrupt service routine and has an Unload routine, the driver must send an IOCTL_INTERNAL_PARALLEL_DISCONNECT_INTERRUPT request in its Unload routine.

The deferred port check routine is called after the parallel port is freed and when there are no pending requests to allocate the port or select an IEEE 1284.3 device. A driver can use the deferred port check routine to enable interrupts.

If a client's interrupt service routine is called when the client does not have a port allocated, the client can attempt to quickly allocate the port by calling the PPARALLEL_TRY_ALLOCATE_ROUTINE (ISR) callback. The client can also use the PPARALLEL_FREE_ROUTINE (ISR) callback to free the port.

Because a parallel port is shared by drivers, the parallel port function driver maintains a list of interrupt service routines and deferred port check routines connected to a parallel port. The parallel port function driver calls all connected interrupt routines and deferred port check routines in the order in which they were connected.