Programming Dedicated Microprocessors

Frontmatter

1. Introduction

Abstract

As the prices of microprocessor chips have fallen, they have increasingly become standard, ‘off the shelf’ components and find their way into a very large proportion of modern electronic equipment and instrumentation. A microprocessor built into a piece of equipment, rather than providing the central processor for a general-purpose microcomputer, is said to be ‘dedicated’ or ‘embedded’. The software which controls such a device is necessarily specialised and is usually called ‘firmware’. This term will be used throughout this book. Strictly speaking, firmware is code which has been placed in non-volatile, read-only memory (ROM) chips, which are built into the circuit with the microprocessor, but this is not always the case, as alternative memory schemes are possible. The various techniques associated with the development of firmware are the subject of this book.

Colin Walls

2. Development Techniques

Abstract

It is probably the development techniques used for firmware which most significantly distinguish it from ordinary software development. Although the aims of the development phases are broadly the same, a number of details are specific to firmware development and it is these which are discussed in this chapter.

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3. Aspects of Hardware Design

Abstract

The principal aim of this book is to aid the transformation of a ‘software engineer’ into a ‘firmware engineer’. As mentioned earlier, the more traditional apprenticeship for a firmware engineer is in hardware. This was the natural evolution, as some knowledge of electronics is required to design firmware successfully. In this chapter, some of the important concepts and ideas behind the design of electronic hardware are presented. It is not intended that the reader should gain a full understanding of electronic engineering, as there are many excellent books which may be studied if further detail is required (Peatman, 1980; Bywater, 1981 ; Berk, 1984).

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4. Interrupts

Abstract

An interrupt, in the general sense, is a change in the flow of a program from the course determined by its instruction sequence, caused by some external influence. Usually the interrupt results in the execution of some specific code to deal with it, before return to the interrupted program.

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5. Z80 Interrupts

Abstract

The interrupt facilities of the Z80 are, for an eight-bit device, quite complex. This serves to enhance the versatility of the chip and provides a very good example for study. A complete understanding of the Z80 capabilities is a useful prerequisite for the study of any device, since the facilities of another microprocessor are quite likely to be a subset of the Z80 facilities.

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6. Input/Output

Abstract

Input/output, or I/O, is, in the general sense, the set of mechanisms by which a program is made ‘aware’ of its environment. I/O is usually envisaged as flow of data, of some form or another, into and out of a piece of software. In a supported environment, I/O is one of the most immediately apparent facilities provided by the operating system to user programs. A program may, in fact, make use of an intermediate facility, a run-time system, for example, to access the system I/O procedures.

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7. Multi-tasking

Abstract

It is difficult to envisage any application of a dedicated microprocessor in which the firmware performs a single, compact and isolated activity. It is much more likely that the microprocessor is required to carry out a number of ‘processes’ or ‘tasks’ (these terms may be used interchangeably; the latter is used in this book), in an apparently simultaneous fashion. Achieving this requirement is the subject of this chapter, with a full description of a practical example the subject of the next.

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8. Implementing a Real-Time Multi-tasking Executive

Abstract

In this chapter, the ideas presented in chapter 7 are put into practice. The development of a real-time multi-tasking executive, for use in firmware applications, is described in some detail. The intention is to provide the reader with enough practical guidance to enable the ideas to be applied to a real firmware application. The executive is called the ‘Firmware Multi-tasking Executive’ (or FMX).

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9. High-level Languages

Abstract

From the beginning of this book it has been assumed that all firmware is written in assembler. It was stated initially that this is the only practical alternative when using eight-bit processors. In most circumstances this is certainly the case, but sometimes the use of a high-level language is feasible and should be considered. This is particularly true if the language permits the inclusion of assembler procedures or ‘insertions’, since some code (interrupt service routines, for example) can hardly ever be written in high level.

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10. Diagnostics

Abstract

During the initial design phase of a piece of electronic equipment, it may be decided that the incorporation of a microprocessor would be advantageous. This conclusion is becoming increasingly common and is the stage at which the firmware engineer should be invited to participate. Having defined the required functions of the microprocessor to achieve the initial design aims, other benefits, which may be provided by the presence of the device, can be considered.

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11. Communications: a Firmware Application

Abstract

It seems only reasonable that a book such as this should have at least one chapter concerned with the application of the concepts and techniques of firmware development. Indeed, it was originally intended to have a final chapter titled simply ‘Firmware Applications’, but this proved to be impractical. Since applications of firmware are, by definition, as diverse and numerous as dedicated applications of microprocessors, this title is more appropriate to another book, rather than a single chapter.

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Backmatter