OS-9

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Home / Programming - OS-9

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Programming the 6809 using OS-9

This section needs help with the Assembler, Pascal and C.

C Programming Language

Introduction

From The C Compiler's User Manual

C was originally developed at the Bel Telephone Laboratories as an implementation language for the UNIX operating system by Brian Kernighan and Dennis Ritchie. They also wrote a book titled The C Programming Language which is universally accepted as the standard for the language. It is an interesting reflection on the language that although no formal industry-wide "standard" was ever developed for C, programs written in C tend to be far more portable between radically different computer systems as compared to so-called "standardized" languages such as BASIC, COBOL, and PASCAL. The reason C is so portable is that the language is so inherently expandable that if some special function is required, the user can create a portable extension to the language, as opposed to the common practice of adding additional statements to the language. For example, the number of special-purpose BASIC dialects defies all reason. A lesser factor is the underlying UNIX operating system, which is also sufficiently versatile to discourage nonstandardization of the language. Indeed, standard C compilers and UNIX are intimately related. Fortunately, the 6809 microprocessor, the OS-9 operating system, and the C language form an outstanding combination. The 6809 was specifically designed to efficiently run high-level languages, and its stack-oriented instruction set and versatile repertoire of addressing modes handle the C language very well. As mentioned previously, UNIX and C are closely related, and because OS-9 is derived from UNIX, it also supports C to the degree that almost any application written in C can be transported from a UNIX system to an OS-9 system, recompiled, and corrected executed.

The Language Implementation

OS-9 C is implemented almost exactly as described in The C Programming Language by Kernighan and Ritchie (hereafter referred to as K&R). A copy of this book, which serves as the language reference manual, is included with each software package. Although this version of C follows the specification faithfully, there are some differences. The differences mostly reflect parts of C that are obsolete or the constraints imposed by memory size limitations.

Differences From the K&R Specification

• Bit fields are not supported.
• Constant expressions for initializers may include arithmetic operators only if all the operands are of type int or char.
• The older forms of assignment operators, =+ or =*, which are recognized by some C compilers, are not supported. You must use the newer forms, +=, *=, etc.
• "#ifdef (#ifndef) ... [#else...] #endif" is supported but "#if <constant expression>" is not.
• It is not possible to extend macro definitions or strings over more than one line of source code.
• The escape sequence for newline '\n' refers to the ASCII carriage return character (used by OS-9 for end-of-line), not linefeed (hex 0A). Programs which use '\n' for end-of-line (which includes all programs in K&R) will still work properly.

Embedded Assembly Language

As versatile as C is, occasionally there are some things that can only be done (or done at maximum speed) in assembly language. The OS-9 C compiler permits user-supplied assembly-language statements to be directly embedded in C source programs.

Basic09

From the Basic09 manual: Basic09 is an enhanced structured BASIC language programming system specially created for the 6809 Advanced Microprocessor. In addition to the standard BASIC language statements and functions, Basic09 includes many of the most useful elements of the Pascal programming language so that programs can be modular, well-structured, and use sophisticated data structures. It also permits full access to almost all of the OS-9 Operating System commands and functions so it can be used as a systems programming language. These features make Basic09 an ideal language for many applications: scientific, business, industrial control, education and more.

Basic09 is unusual in that it is an Interactive Compiler that has the best of both kinds of language system: it gives the fast execution speed typical of compiler languages plus the ease of use and memory space efficiency typical of interpreter languages. Basic09 is truly a complete programming system that includes a powerful text editor, multi-pass compiler, run-time interpreter, high-level interactive debugger, and a system executive. Each of these components was carefully integrated so the user "sees" a friendly, highly interactive programming resource that provides all the tools and helpful "extra" facilities needed for fast, accurate creation and testing of structured programs.

• The Structure of I-Code