IBM Version 4 Chapter 7. Machine Interface Programming

Chapter 7. Machine Interface Programming

This chapter is for programmers interested in creating machine interface (MI) pro-

grams. While some MI instructions are discussed within the context of how to

develop MI programs, this chapter makes no attempt to review the full range of MI

instructions. The goal of this chapter is to provide a sufficient base of knowledge

so that you can begin to use the MI language. After reading this chapter, you

should be able to develop, create, run, and debug an AS/400 MI program. When

reading this chapter, you will need access to the

System API Reference

SC41-5801, and the

Machine Interface Functional Reference

, SC41-5810, because

these two books are referred to extensively.

Machine Interface Instructions—Introduction

Programs and procedures are the two basic units of execution on the AS/400. Pro-

grams come in two flavors: the original program model (OPM) and the Integrated

Language Environment (ILE). MI programs can be created only for the OPM envi-

ronment. If you require ILE support in the development of your applications, use

ILE C and its built-in MI support.

In the OPM environment, a program is comprised of two basic components: the

object definition table (ODT) and an instruction stream. In the case of MI pro-

grams, the program is created using the Create Program (QPRCRTPG) API. This

API is documented in the

System API Reference

The ODT is the means for defining all objects1 that are referred to by the MI

instruction stream. An ODT definition of an object does not actually allocate

storage for the object. It does, however, define when and how much storage is to

be allocated and also the attributes of the storage (for example, the data type of the

object). The ODT is built from the declare (DCL) statements found in the source

used to create a program. Because DCL statements are actually instructions to the

QPRCRTPG API and not MI instructions, they are defined in the QPRCRTPG API.

The types of objects that can be declared are:

Scalar

Pointer

Machine space pointer

Operand list

Instruction definition list

Exception description

Space

Constant

The instruction stream defines the set of operations to be performed by the

program. The instruction stream is built from the MI instructions found in the

source used to create a program. The various MI instructions that you can use are

defined in the

Machine Interface Functional Reference

1The term

objects

in this chapter refers to program data elements and not OS/400 object types such as a *FILE, *PGM, *USRPRF,

and so on.