HP 3000 Manuals

Switch Programming User's Guide

Overview 

This overview presents mixed-mode procedure calls in the CM --> NM
direction in two ways:

 *  Schematic flow-of-control diagram

 *  Stepwise sequence of events

Flow of Control:  CM --> NM 

The flow of control for mixed-mode procedure calls in the direction CM
--> NM is illustrated in Figure 4.1:


          Figure 4.1.  CM --> NM Switch Summary 1

Stepwise Switch to NM 

A mixed-mode procedure call in the direction CM --> NM involves the
following steps, as indicated in Figure 4.1:

1.               The CM code needing to access an NM routine calls
                 Switch, either by means of in-line code or a Switch
                 stub.

2.               The in-line code or CM Switch stub sets up the data
                 structures and parameters required by Switch and makes a
                 call to either the HPSWTONMNAME intrinsic or the
                 HPLOADNMPROC and HPSWTONMPLABEL intrinsics.

3.               HPSWTONMNAME or HPSWTONMPLABEL calls the NM routine,
                 after preparing the NM registers as though the call was
                 being made from Native Mode.

4.               The NM routine executes as though called from Native
                 Mode and returns the functional return value (if any) to
                 the calling Switch intrinsic.  Reference parameters are
                 modified by the NM routine.

5.               If the NM routine has a functional return value,
                 HPSWTONMNAME or HPSWTONMPLABEL copies the value back to
                 the CM stack.

6.               The stub or in-line code checks whether the Switch
                 operation was successful and then control returns to the
                 CM routine.


NOTE  HPSWTONMNAME or a combination of HPLOADNMPROC and HPSWTONMPLABEL
      are the system intrinsics called to pass CM values and parameters
      to Native Mode, to change the execution mode, and to invoke an NM
      routine.  HPSWTONMNAME, HPLOADNMPROC, and HPSWTONMPLABEL reside in
      the CM system library, SL.PUB.SYS. The only difference between
      using HPSWTONMNAME and HPSWTONMPLABEL is the manner in which the
      target routine is identified.

MPE/iX 5.0 Documentation