File Name: embedded systems programming in c and assembly .zip
I consider that the golden rule requires that if I like a program I must share it with other people who like it. Software sellers want to divide the users and conquer them, making each user agree not to share with others.
I refuse to break solidarity with other users in this way. I cannot in good conscience sign a nondisclosure agreement or a software license agreement. So that I can continue to use computers without dishonor, I have decided to put together a sufficient body of free software so that I will be able to get along without any software that is not free. The only thing that has really changed is that you need to have an understanding of the target hardware platform.
Furthermore, each target hardware platform is unique—for example, the method for communicating over a serial interface can vary from processor to processor and from platform to platform. We focus on the use of open source software tools in this edition of the book. Open source solutions are very popular and provide tough competition for their commercial counterparts.
When build tools run on the same system as the program they produce, they can make a lot of assumptions about the system. This is typically not the case in embedded software development, where the build tools run on a host computer that differs from the target hardware platform.
There are a lot of things that software development tools can do automatically when the target platform is well defined. For example, if all of your programs will be executed on IBM-compatible PCs running Windows, your compiler can automate—and, therefore, hide from your view—certain aspects of the software build process. Embedded software development tools, on the other hand, can rarely make assumptions about the target platform. Instead, the user must provide some of her own knowledge of the system to the tools by giving them more explicit instructions.
The process of converting the source code representation of your embedded software into an executable binary image involves three distinct steps:. Each of the source files must be compiled or assembled into an object file. All of the object files that result from the first step must be linked together to produce a single object file, called the relocatable program.
Physical memory addresses must be assigned to the relative offsets within the relocatable program in a process called relocation. The result of the final step is a file containing an executable binary image that is ready to run on the embedded system.
The embedded software development process just described is illustrated in Figure In this figure, the three steps are shown from top to bottom, with the tools that perform the steps shown in boxes that have rounded corners.
Each of these development tools takes one or more files as input and produces a single output file. More specific information about these tools and the files they produce is provided in the sections that follow.
Each of the steps of the embedded software build process is a transformation performed by software running on a general-purpose computer. To distinguish this development computer usually a PC or Unix workstation from the target embedded system, it is referred to as the host computer. The compiler, assembler, linker, and locator run on a host computer rather than on the embedded system itself.
Yet, these tools combine their efforts to produce an executable binary image that will execute properly only on the target embedded system. This split of responsibilities is shown in Figure These tools are extremely popular with embedded software developers because they are freely available even the source code is free and support many of the most popular embedded processors.
We will use features of these specific tools as illustrations for the general concepts discussed. Once understood, these same basic concepts can be applied to any equivalent development tool. The job of a compiler is mainly to translate programs written in some human-readable language into an equivalent set of opcodes for a particular processor.
Everything in this section applies equally to compilers and assemblers. Together these tools make up the first step of the embedded software build process.
Of course, each processor has its own unique machine language, so you need to choose a compiler that produces programs for your specific target processor. In the embedded systems case, this compiler almost always runs on the host computer. A compiler such as this—that runs on one computer platform and produces code for another—is called a cross-compiler.
The use of a cross-compiler is one of the defining features of embedded software development. The GNU C compiler gcc and assembler as can be configured as either native compilers or cross-compilers.
These tools support an impressive set of host-target combinations. The gcc compiler will run on all common PC and Mac operating systems. This is a specially formatted binary file that contains the set of instructions and data resulting from the language translation process. Although parts of this file contain executable code, the object file cannot be executed directly.
In fact, the internal structure of an object file emphasizes the incompleteness of the larger program. The contents of an object file can be thought of as a very large, flexible data structure.
Although many compilers particularly those that run on Unix platforms support standard object file formats such as COFF and ELF, some others produce object files only in proprietary formats. Most object files begin with a header that describes the sections that follow. Each of these sections contains one or more blocks of code or data that originated within the source file you created.
However, the compiler has regrouped these blocks into related sections. For example, in gcc all of the code blocks are collected into a section called text , initialized global variables and their initial values into a section called data , and uninitialized global variables into a section called bss. There is also usually a symbol table somewhere in the object file that contains the names and locations of all the variables and functions referenced within the source file.
Parts of this table may be incomplete, however, because not all of the variables and functions are always defined in the same file. These are the symbols that refer to variables and functions defined in other source files. And it is up to the linker to resolve such unresolved references. All of the object files resulting from the compilation in step one must be combined. The object files themselves are individually incomplete, most notably in that some of the internal variable and function references have not yet been resolved.
The job of the linker is to combine these object files and, in the process, to resolve all of the unresolved symbols. The output of the linker is a new object file that contains all of the code and data from the input object files and is in the same object file format.
It does this by merging the text , data , and bss sections of the input files. When the linker is finished executing, all of the machine language code from all of the input object files will be in the text section of the new file, and all of the initialized and uninitialized variables will reside in the new data and bss sections, respectively.
While the linker is in the process of merging the section contents, it is also on the lookout for unresolved symbols. For example, if one object file contains an unresolved reference to a variable named foo , and a variable with that same name is declared in one of the other object files, the linker will match them.
The unresolved reference will be replaced with a reference to the actual variable. For example, if foo is located at offset 14 of the output data section, its entry in the symbol table will now contain that address.
It is a command-line tool that takes the names of all the object files, and possibly libraries, to be linked as arguments. With embedded software, a special object file that contains the compiled startup code, which is covered later in this section, must also be included within this list.
The GNU linker also has a scripting language that can be used to exercise tighter control over the object file that is output. If the same symbol is declared in more than one object file, the linker is unable to proceed.
It will likely complain to the programmer by displaying an error message and exit. On the other hand, if a symbol reference remains unresolved after all of the object files have been merged, the linker will try to resolve the reference on its own. The reference might be to a function, such as memcpy , strlen , or malloc , that is part of the standard C library, so the linker will open each of the libraries described to it on the command line in the order provided and examine their symbol tables.
If the linker thus discovers a function or variable with that name, the reference will be resolved by including the associated code and data sections within the output object file. Unfortunately, the standard library routines often require some changes before they can be used in an embedded program.
One problem is that the standard libraries provided with most software development tool suites arrive only in object form. You only rarely have access to the library source code to make the necessary changes yourself. Thankfully, a company called Cygnus which is now part of Red Hat created a freeware version of the standard C library for use in embedded systems.
This package is called newlib. The library can then be linked with your embedded software to resolve any previously unresolved standard library calls. In other words, the program is complete except for one thing: no memory addresses have yet been assigned to the code and data sections within. The addresses of the symbols in the linking process are relative. In fact, if there is an operating system, the code and data of which it consists are most likely within the relocatable program too.
The entire embedded application—including the operating system—is frequently statically linked together and executed as a single binary image. One of the things that traditional software development tools do automatically is insert startup code : a small block of assembly language code that prepares the way for the execution of software written in a high-level language.
Each high-level language has its own set of expectations about the runtime environment. For example, programs written in C use a stack.
Space for the stack has to be allocated before software written in C can be properly executed. That is just one of the responsibilities assigned to startup code for C programs. Most cross-compilers for embedded systems include an assembly language file called startup.
The location and contents of this file are usually described in the documentation supplied with the compiler. Startup code for C programs usually consists of the following series of actions:. Typically, the startup code will also include a few instructions after the call to main. These instructions will be executed only in the event that the high-level language program exits i.
Depending on the nature of the embedded system, you might want to use these instructions to halt the processor, reset the entire system, or transfer control to a debugging tool. Because the startup code is often not inserted automatically, the programmer must usually assemble it himself and include the resulting object file among the list of input files to the linker.
He might even need to give the linker a special command-line option to prevent it from inserting the usual startup code. Working startup code for a variety of target processors can be found in a GNU package called libgloss. In some cases, a debug monitor or ROM monitor is the first code executed when the board powers up. In the case of the Arcom board, there is a debug monitor called RedBoot.
Many programmers are more comfortable writing in C, and for good reason: C is a mid-level language in comparison to Assembly, which is a low-level language , and spares the programmers some of the details of the actual implementation. However, there are some low-level tasks that either can be better implemented in assembly, or can only be implemented in assembly language. Also, it is frequently useful for the programmer to look at the assembly output of the C compiler, and hand-edit, or hand optimize the assembly code in ways that the compiler cannot. Assembly is also useful for time-critical or real-time processes, because unlike with high-level languages, there is no ambiguity about how the code will be compiled. The timing can be strictly controlled, which is useful for writing simple device drivers.
C programming for embedded microcontroller experience with assembly language P. C programming for embedded microcontroller systems.
One of the best features of C is that it is not tied to any particular hardware or system. Format : Pdf. Pages : Embedded C programming language is an extension to the traditional C programming language, that is used in embedded systems. A lot has changed since Mckinal Danny Causey. No programming experience is necessary!
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Earlier, many embedded applications were developed using assembly level programming. However, they did not provide portability. However, it was the C language that got extensive acceptance for embedded systems, and it continues to do so. The C code written is more reliable, scalable, and portable; and in fact, much easier to understand. Embedded C Programming is the soul of the processor functioning inside each and every embedded system we come across in our daily life, such as mobile phones, washing machines, and digital cameras. Each processor is associated with embedded software.
I consider that the golden rule requires that if I like a program I must share it with other people who like it. Software sellers want to divide the users and conquer them, making each user agree not to share with others. I refuse to break solidarity with other users in this way. I cannot in good conscience sign a nondisclosure agreement or a software license agreement. So that I can continue to use computers without dishonor, I have decided to put together a sufficient body of free software so that I will be able to get along without any software that is not free. The only thing that has really changed is that you need to have an understanding of the target hardware platform. Furthermore, each target hardware platform is unique—for example, the method for communicating over a serial interface can vary from processor to processor and from platform to platform.
Principles of C programming are introduced gradually, building on skill sets and knowledge. This book demonstrates the programming methodology and tools used by most professionals in embedded design, and will enable you to apply your knowledge and programming skills for any real-life application. Providing a step-by-step guide to the subject matter, this book will encourage you to alter, expand, and customize code for use in your own projects.
Embedded C is a set of language extensions for the C programming language by the C Standards Committee to address commonality issues that exist between C extensions for different embedded systems. In , the C Standards Committee extended the C language to address such capabilities by providing a common standard for all implementations to adhere to.
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Я так испугалась, увидев .
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