HP 3000 Manuals

Switch Programming User's Guide

SWitch Assist Tool (SWAT) 

The SWitch Assist Tool (SWAT) is an interactive utility that produces the
Switch stub source code you can use to make mixed-mode procedure calls in
the NM--> CM direction.  SWAT prompts you for information regarding the
called other-mode procedure and its parameters.  In response, SWAT builds
source code containing the data structures and logic required to use
Switch.

Figure 2.1 illustrates a situation that requires invocation of Switch:


          Figure 2.1.  Mixed-mode Procedure Call

Procedure Z represents an entity that is not supplied in the Native Mode
environment.  The SWAT utility can help you handle such unresolved
references.

Tools like SWAT enable you to improve performance of migrated
applications with a minimum of effort and concern about the architectural
differences.  You can use SWAT prior to installation to prepare the
source code for Switch stubs ahead of time, as well as after the MPE
XL-based system is up and running.

Who Uses SWAT? 

If you develop applications and subsystems for the HP 3000, then you may
be interested in migrating existing applications to MPE XL-based systems.
Migrating an application entirely to Native Mode is the preferred
approach.  However, due to considerations such as the size of the
application, the availability of shared procedures, and the language of
implementation (SPL, in particular), you may have no choice but to mix
modes of execution.  The most efficient means for accomplishing this task
is to migrate those applications in a phased approach.  That requires the
mixing of Compatibility Mode and Native Mode code.

Switch provides the ability to make mixed-mode procedure calls.  SWAT
helps you use Switch to run portions of an application in Compatibility
Mode and portions in Native Mode.  You will be particularly interested in
using SWAT if you have high-level applications that call user-written SPL
routines or if your applications call SPL routines for which the source
code is not available.  Because these two types of routines cannot run in
Native Mode, they must either be rewritten entirely or execute in
Compatibility Mode.  Once you have decided which procedures or modules of
your application are to remain in Compatibility Mode, you can use SWAT to
generate the necessary Switch stubs to make the switching transparent.

Features 

The features of the Switch Assist Tool include the following:

 *  SWAT's user interface is interactive, flexible, and easy-to-use.

 *  SWAT generates standardized Switch stub source code in the HP
    Pascal/XL programming language.

 *  SWAT facilitates user modification by keeping the source file output
    in a text file.

 *  SWAT fully supports most programming options, within the limitations
    of Switch and MPE XL.

 *  SWAT automatically appends the appropriate compiler commands to the
    generated source code.

 *  SWAT is available upon installation of MPE XL-based systems.

 *  SWAT standardizes management of the interface between Compatibility
    Mode and Native Mode.

 *  SWAT generates the source code required for most possible types of
    mixed-mode procedure calls in the NM--> CM direction.

Benefits 

SWAT's primary benefit is the programmer support it provides by
alleviating much of the complexity faced in making mixed-mode procedure
calls.  It also increases the quality of Switch stub source code by
generating standardized source code.

To code a working Switch stub manually, you need the following:

 *  Knowledge of the stack architecture of MPE V/E-based systems and the
    register assignments of 900 Series machines

 *  Familiarity with two system programming languages (SPL and HP
    Pascal/XL)

 *  Details of the calling sequences, parameter types, and return values
    of the target procedures

 *  Familiarity with the complexities of the Switch intrinsics

 *  Access to the library management of both CM and NM environments

 *  Knowledge of how to handle condition codes and status words that are
    returned when mixed-mode procedure calls are made

By helping you meet these concerns, SWAT helps to make the migration
process as smooth and easy as possible.

Furthermore, because much of the information and data structures required
by Switch are repetitive in nature and must be duplicated for each
parameter passed through Switch, SWAT eliminates much of the tedium
otherwise associated with manually coding Switch stubs.

In summary, SWAT serves to increase your productivity and reduce the time
required to migrate applications to a Series 900 machine.  SWAT benefits
those who are migrating application programs and subsystems to MPE
XL-based systems in the following ways:

 *  SWAT incorporates into the logic of the tool the systems and
    programming knowledge required to produce Switch stub code.

 *  SWAT eliminates many of the repetitious aspects of stub coding.

 *  SWAT helps assure the correct execution of mixed-mode procedure calls
    by generating standardized Switch stub source code as its output.

 *  For those who prefer to code Switch stubs manually, or in some
    instances must do so, SWAT provides examples of good coding practices
    and can act as a template for advanced stubs.

Switch Stub Operation 

Figure 2.2 demonstrates how Switch stubs and the Switch subsystem fit
into the overall flow of program execution:


          Figure 2.2.  Switch Scenario

The Switch stub acts as an interceptor/intermediary that calls the Switch
subsystem and passes it the parameters of the called procedure and any
other information required by Switch.  Switch itself calls the other-mode
procedure.

MPE/iX 5.0 Documentation