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Translation Tools

Preprocessors, Interpreters, Compilers, and Linkers

After the source code has been written, it needs to be translated into

machine code, since machine code is the only language the hardware can directly

execute. All other languages need development tools that generate the

corresponding machine code the hardware will understand. This mechanism

usually includes one or some combination of preprocessing, translation, and/or

interpretation machine code generation techniques. These mechanisms are

implemented within a wide variety of translating development tools.

Preprocessing is an optional step that occurs either before the translation or

interpretation of source code, and whose functionality is commonly implemented by

a preprocessor.

The preprocessors role is to organie and restructure the source code to ma!e

translation or interpretation of this code easier. The preprocessor can be a separate

entity, or can be integrated within the translation or interpretation unit.

"any languages convert source code, either directly or after having been

preprocessed, to target code through the use of a compiler, a program which

generates some target language, such as machine code, #ava byte code, etc., from

the source language, such as assembly, $, #ava, etc

A compiler typically translates all of the source code to a target code at one time.

As is usually the case in embedded systems, most compilers are located on the

programmers host machine and generate target code for hardware platforms that

differ from the platform the compiler is actually running on.

These compilers are commonly referred to as cross-compilers.

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%ome generate machine code while others generate other high&level languages,

which then require what is produced to be run through at least one more

compiler.

%till other compilers generate assembly code, which must be run through an

assembler.

After all the compilation on the programmers host machine is completed, the

remaining target code file is commonly referred to as an object filedepending

on the programming language used.

A linker integrates this ob'ect file with any other required system libraries,

creating executable binary file, either directly onto the boards memory or

ready to be transferred to the target embedded systems memory by a loader.

(ne of the fundamental strengths of a translation process is based upon the

concept of software placement )referred to as ob'ect placement*, the ability to divide

the software into modules and relocate these modules of code and data anywhere in

memory.

This is an especially useful feature in embedded systems, because+

mbedded designs can contain several different types of physical

memory

They typically have a limited amount of memory compared to

other types of computer systems

"emory can typically become very fragmented and

defragmentation functionality is not available out&of&the&box

or too expensive

$ertain types of embedded software may need to be executed from a particular

memory location.

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This software placement capability can be supported by the master processor, which

supplies specialied instructions that can be used to generate -position independent

code, it could be separated by the software translation tools alone.

here a compiler/assembler produces relocatable modules, process instructionformats, and may do some translation of relative to physical )absolute*

addresses. An interpreter generates )interprets* machine code one source code

line at a time from source code or target code generated by a intermediate

compiler on the host system

An embedded developer can ma!e a big impact in terms of selecting translation

tools for a pro'ect by understanding how the compiler wor!s and, if there are

options, by selecting the strongest possible compiler.

This is because the compiler, in large part, determines the sie of the executable

code by how well it translates the code. This not only means selecting a

compiler based on support of the master processor, particular system

software, and the remaining toolset )a compiler can be acquired separately, as

part of a starter !it from a hardware vendor, andor integrated within an 01*. 0t

also means selecting a compiler based upon a feature set that optimies the

codes simplicity, speed, and sie.

(ptimiing the code for performance means that the compiler understands and

ma!es use of the various features of a particular 0%A, such as math operations,

the register set, !nowing the various types of on&chip 2(" and 2A", the

number of cloc! cycles for various types of accesses, etc. 3y understanding

how the compiler translates the code, a developer can recognie what support is

provided by the compiler and learn.