The OPEN call has no parameters. It grants access to the driver from a particular process. The driver ensures that only one OPEN is accepted by the link at any one time. When OPEN is processed, the driver attempts to reserve access to hardware resources such as interrupt vectors; the OPEN is rejected if this fails.
After a successful OPEN request, the driver expects to receive the following IOCTL commands:
SET_EVENT_HANDLE
SET_INTERFACE_RECORD
SET_LINK_CHARACTERISTICS
Of these, the first two can be performed in any order, but both should be issued before calling SET_LINK_CHARACTERISTICS.
When these three calls have been successfully performed by the SNALink, the driver is ready for information transfer.