How to Access the .XPP Driver
All .XPP driver routines can be executed either synchronously (meaning that
the application cannot continue until the routine is completed) or
asynchronously (meaning that the application is free to perform other tasks
while the routine is executing).
XPP calls are made from a high-level language in the same manner as MPP
and ATP calls, with the exception that when making XPP calls the caller must
set the XPP driver's refnum. This refnum is returned in the OpenXPP call's parameter block.
A high-level language variant record has been defined for all XPP calls. This
parameter block is detailed in Figure 4. The first four fields (which are the
same for all calls) are automatically filled in by the Device Manager. Ths csCode field is automatically filled in by the high-level language, depending on
which call is being made. The caller must, however, set the ioRefnum field to
XPP's reference number, as returned in the OpenXPP call. the ioVRefnum field is unused.
Note that the parameter block is defined so as to be the maximum size used by
any call. Different calls can take different size parameter blocks, each call
requiring a certain minimum size. Callers are free to abbreviate the
parameter block when appropriate.
With each routine, a list of parameter block fields used by the call is also
the csCode field equal to the code corresponding to the function being called.
The number next to each field name indicates the byte offset of the field from
the start of the parameter block pointed to by A0; only assembly- language
programmers need to be concerned with it. An arrow next to each parameter
name indicates whether it's an input, output, or input/output parameter.
the ioResult field. Each routine description lists all the applicable result
codes, along with a short description of what the result code means.