HP 3000 Manuals

Switch Programming User's Guide

Overview 

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

 *  Schematic flow-of-control diagram

 *  Stepwise sequence of events

Flow of Control:  NM--> CM 

The flow of control for mixed-mode procedure calls in the direction NM-->
CM is illustrated in Figure 3.1:


          Figure 3.1.  NM--> CM Switch Summary 1

Stepwise Switch to CM 

A mixed-mode procedure call in the direction NM--> CM involves the
following steps, as indicated in Figure 3.1:

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

2.               The in-line code or NM Switch stub sets up the data
                 structures and parameters required by Switch and makes a
                 call to the HPSWITCHTOCM intrinsic (call by name), or
                 the HPLOADCMPROCEDURE and HPSWITCHTOCM intrinsics (call
                 by plabel).

3.               HPSWITCHTOCM calls the CM routine and passes the
                 parameters, translating addresses and/or copying data to
                 Compatibility Mode as required by their type, size, and
                 location.

4.               The CM routine executes using the passed parameters and
                 returns its data values to HPSWITCHTOCM.

5.               HPSWITCHTOCM receives the data values returned by the CM
                 routine, back-translating addresses and recopying data
                 as needed.

6.               HPSWITCHTOCM returns the translated values to the
                 caller.  The stub or in-line code checks whether the
                 Switch operation was successful and then control returns
                 to the NM routine.


NOTE  HPSWITCHTOCM is the system intrinsic that makes NM parameters
      addressable to Compatibility Mode, changes the execution mode, and
      invokes the CM routine.  HPSWITCHTOCM and HPLOADCMPROCEDURE reside
      in the NM system library, NL.PUB.SYS.

MPE/iX 5.0 Documentation