Thanks for your comment.
I think this unsolicited status problem is not a problem of SBP-2 driver
In Macintosh OS, a PDEF code resource of a higher level printer driver
uses PBWrite(&pb, Async) and PBRead(&pb, Async).
In Windows OS, a SPOOLER user mode application usually uses WriteFile()
As PBRead() or ReadFile() is higher level interface, naturally these
abstracted from a specific device level driver. In Mac OS8, a Printer
PDEFs shall be abstracted from the FSL. Also in Windows, a SPOOLER
shall be abstracted from the SBP-2 Class Driver. Usually these input
are associated with input queues for normal reverse data path from