Microprocessor 5

Software and Hardware Aspects of Development, Debugging and Testing - The Microcomputer

Philippe Darche

• Publisher: Wiley-ISTE
• Year: 2020
• ISBN:
  9781119801733
• Edition: 1
• Topic: Ciencia de la computación
• Subtopic: Ingeniería computacional

Since its commercialization in 1971, the microprocessor, a modern and integrated form of the central processing unit, has continuously broken records in terms of its integrated functions, computing power, low costs and energy saving status. Today, it is present in almost all electronic devices. Sound knowledge of its internal mechanisms and programming is essential for electronics and computer engineers to understand and master computer operations and advanced programming concepts. This book in five volumes focuses more particularly on the first two generations of microprocessors, those that handle 4- and 8- bit integers. Microprocessor 5 – the fifth and final volume of this series of books – first presents the hardware and software aspects of the development chain of a microprocessor-based digital system. Finally, to round up the series and offer a historical perspective, the architectures of the first microcomputers are detailed. A comprehensive approach is used, with examples drawn from current and past technologies that illustrate theoretical concepts, making them accessible.

PART 1

The first part of this last volume is divided into two chapters. The first presents the software development chain, and the second illustrates the hardware and software tools used in development and testing.

1
Development Chain

This chapter is focused on the software development chain for a microprocessor-based system. The different steps and their associated tools, including the first, the assembler, are examined. The debugging and testing aspects have taken on greater importance as hardware and software have grown more complex and become embedded in systems. These software and hardware tools are then described in detail. At first conceived to be used at the printed circuit level, they must be integrated progressively. To conclude, assembly language, a first level symbolic language, will be surveyed. The reader who is interested in a specific processor should refer to documentation from the relevant manufacturer. In addition, we will not here make a distinction between microprocessor and microcontroller because, in the latter case, we will only examine the “computation” component, that is, the processor, without addressing the other two subsystems, which are Input/Output (I/O) and RAM/ROM (Random Access/Read-Only Memory), including programmable memory, as relates to the latter type.

NOTE.– An understanding of the concepts of data representation and arithmetic operations in a computer is assumed. Otherwise, cf. Darche (2000). This will also be the case for logical operators. On this subject, cf. Darche (2002).

1.1. Layers of languages, stages of development and tools

The processor uses two-state logic. Instruction codes and data are therefore expressed in binary. This is machine language. Manipulating such data is not humanly possible for a program longer than about a hundred lines. The first computers were programmed in this language, and the program (i.e. machine code and data) was entered in binary format using switches as input peripherals. Because of the difficulty of use, an additional layer of language closer to natural language (English) was therefore necessary. This language is called “Assembly Language,” which is abbreviated in this work as AL. The term assembly emerged from the EDSAC project (Electronic Delay Storage Automatic Calculator, Wilkes 1950, 1951) defining the action of reading subprograms from a symbolic instruction tape (a letter), translating them into binary, and making them executable by the main program (modern functions of a link editor and loading program combined). This mechanism is attributed to David J. Wheeler (Wheeler 1950). Excluding machine-oriented language, assembly language is therefore the processor’s base programming language. It is referred to as symbolic. This indicates that it manipulates symbolic information, instruction words, variables and labels primarily. A specific assembly language corresponds to a single Instruction Set Architecture (ISA, cf. § V1-3.5). Assembly instructions are referred to using a form of abbreviated writing called operation code (or opcode) mnemonic (cf. § V4-2.1). An opcode mnemonic is a symbolic representation of a machine code. The assembler is the computing tool that translates between the symbolic name and the binary value. The first assembler was written by Nathaniel Rochester for the IBM 701 (1954). Recall that instructions in machine language, also called machine code or sometimes hard code (Bell 1973), are a series of binary instructions that are read and executed by the microprocessor. Figure 1.1 shows an example of assembly with two lines of instructions for the 8086 microprocessor. The assembler translated the mnemonics into machine code, here expressed in base 16 for readability. This tool is specialized for a processor or a family of processors. There is no efficiency loss between assembly languages and binary because the translation is direct. This is not the case for High-Level (programming) Language (HLL) compilers, where one high-level instruction (i.e. statement) corresponds to a sequence of several instructions in assembly language.

Figure 1.1. Example of lines from a program written in 80x86 assembly language

1.1.1. Levels of languages

Programming languages evolve in the direction of the increasing ease of programming by making it possible to manipulate higher-level abstractions, for example at the level of data structures or operators. Assembly language is downstream from high-level language, as shown in Figure 1.2. A language referred to as high level is as close as possible to human language. This is why machine and assembly languages are called Low-Level (programming) Languages¹ (LLL). To move from one level to a lower level, it is necessary to use a translator that will substitute a source-language instruction with a series of instructions belonging to the lower-level (target) language. Each instruction in machine language that is executed will give rise to a series of commands inside the microprocessor, or micro-operations. In a micro-programmed archite...