PPARALLEL_TRY_SELECT_ROUTINE callback function (parallel.h)

Article
10/21/2021

The PPARALLEL_TRY_SELECT_ROUTINE-typed callback routine selects an IEEE 1284.3 daisy chain device or an IEEE 1284 end-of-chain device that is attached to a parallel port. The system-supplied function driver for parallel ports supplies this routine.

Syntax

PPARALLEL_TRY_SELECT_ROUTINE PparallelTrySelectRoutine;

NTSTATUS PparallelTrySelectRoutine(
  [in] PVOID TrySelectContext,
  [in] PVOID TrySelectCommand
)
{...}

Parameters

[in] TrySelectContext

Pointer to the device extension of a parallel port's functional device object (FDO).

[in] TrySelectCommand

Pointer to a PARALLEL_1284_COMMAND structure. The caller specifies the following members:

ID

Specifies the 1284.3 device ID.

CommandFlags

Specifies a bitwise OR of zero or more of the following flags:

Value	Description
PAR_END_OF_CHAIN_DEVICE	Specifies an end-of-chain device.
PAR_HAVE_PORT_KEEP_PORT	Specifies that the caller has the port allocated and to keep the port allocated.

Return value

Return code	Description
STATUS_SUCCESS	The device was selected.
STATUS_INVALID_PARAMETER	The device ID is not valid.
STATUS_PENDING	The caller did not specify PAR_HAVE_PORT_KEEP_PORT, and the parallel port is already allocated.
STATUS_UNSUCCESSFUL	The caller has allocated the parallel port, but the system-supplied function driver for parallel ports could not select the specified parallel device.

Remarks

To obtain a pointer to the system-supplied PPARALLEL_TRY_SELECT_ROUTINE callback, a kernel-mode driver uses an IOCTL_INTERNAL_GET_PARALLEL_PNP_INFO request, which returns a PARALLEL_PNP_INFORMATION structure. The TrySelectDevice member of the PARALLEL_PNP_INFORMATION structure is a pointer to this callback.

A kernel-mode driver can use an IOCTL_INTERNAL_SELECT_DEVICE request or the PPARALLEL_TRY_SELECT_ROUTINE callback to select a parallel device on a parallel port. The parallel port function driver queues a select request if the parallel port is already allocated. However, the PPARALLEL_TRY_SELECT_ROUTINE callback does not queue a select request, and the routine returns immediately if the port cannot be allocated.

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. To ensure success, a client must use an IOCTL_INTERNAL_SELECT_DEVICE request. (The parallel port function driver queues, and subsequently processes, port allocate requests and device select requests in the order in which select device requests are received.)

For more information, see Selecting and Deselecting an IEEE 1284 Device Attached to a ParallelPort.

Requirements

Requirement	Value
Target Platform	Desktop
Header	parallel.h (include Parallel.h)
IRQL	<=DISPATCH_LEVEL

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