To ensure success, a client must use an IOCTL_INTERNAL_SELECT_DEVICE request. Note If a client uses only the PPARALLEL_TRY_SELECT_ROUTINE callback to attempt to select a parallel device, and other clients are contending for the parallel port, the system-supplied function driver for parallel ports might never allocate the port to the client.

The client can cancel a select request at any time because of an acceptable time-out delay or some other device-specific condition. After the parallel port function driver dequeues the select request, it attempts to allocate the port and to select the IEEE 1284.3 device. The select requests require the least handling by the client because the system-supplied function driver for parallel ports queues the select request for the client if the parallel port is allocated by another client. The DeselectDevice member is a pointer to a PPARALLEL_DESELECT_ROUTINE callback, which selects an IEEE 1284.3 daisy chain device or an IEEE 1284 end-of-chain device that is attached to a parallel port. The TrySelectDevice member is a pointer to a PPARALLEL_TRY_SELECT_ROUTINE callback, which deselects an IEEE 1284.3 daisy chain device or an IEEE 1284 end-of-chain device that is attached to a parallel port. This request returns a PARALLEL_PNP_INFORMATION structure that includes the following pointers to system-supplied callbacks:

A client can select and deselect an IEEE 1284.3 device attached to a parallel port by using the following internal device control requests:Ī kernel-mode driver can also use the system-supplied parallel device callback routines that are obtained by using an IOCTL_INTERNAL_GET_PARALLEL_PNP_INFO request.

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