HandBooks Professional Java-C-Scrip-SQL part 211 pptx

reentrant Refers to software that can be executed multiple times simultaneously.. reset address The address from which the first instruction will be fetched after the processor is powe

recursive

Refers to software that calls itself Recursion should generally be avoided in

an embedded system because it frequently requires a large stack

reentrant

Refers to software that can be executed multiple times simultaneously A reentrant function can be safely called recursively or from multiple tasks The key to making code reentrant is to ensure mutual exclusion whenever accessing global variables or shared registers

register

A memory location that is part of a processor or a peripheral In other words, it's not normal memory Generally, each bit or set of bits within the register controls some behavior of the larger device

relocatable

A file containing object code that is almost ready for execution on the target The final step is to use a locator to fix the remaining relocatable addresses within the code The result of that process is an executable

reset address

The address from which the first instruction will be fetched after the

processor is powered on or reset

reset code

A small piece of code that is placed at the reset address The reset code is usually written in assembly language and might simply be the equivalent of

"jump to the startup code."

reset vector

See reset address

S

SRAM

Static Random-Access Memory A type of RAM that retains its contents as long as power is supplied to it Data stored in an SRAM is lost when the system is powered down or reset

scheduler

The part of an operating system that decides which task to run next This decision is based on the readiness of each task, their relative priorities, and the specific scheduling algorithm implemented

semaphore

A data structure that is used for intertask communication Semaphores are usually provided by the operating system

simulator

A debugging tool that runs on the host and pretends to be the target

processor A simulator can be used to test pieces of the software before the embedded hardware is available Unfortunately, attempts to simulate

interactions with complex peripherals are often more trouble than they are worth

software interrupt

An interrupt that is generated by a software instruction Software interrupts are commonly used to implement breakpoints and operating system entry points Compare with trap

stack

An area of memory that contains a last-in-first-out queue of storage for parameters, automatic variables, return addresses, and other information that must be maintained across function calls In multitasking situations, each task generally has its own stack

stack frame

An area of the stack associated with a particular function call

startup code

A piece of assembly language code that prepares the way for software

written in a high-level language Most C/C++ cross-compilers come with startup code that you can modify, compile, and link with your embedded programs

T

target

Another name for the embedded system This term is usually used during software development, to distinguish the embedded system from the host with which it communicates

task

The central abstraction of an operating system Each task must maintain its own copy of the instruction pointer and general-purpose registers Unlike processes, tasks share a common memory space and must be careful to avoid overwriting each other's code and data

thread

Another name for a task This name is more common in operating systems that support processes A task is simply a thread in a single-process system

tracepoint

Similar to a breakpoint except that a counter is incremented rather than stopping the program Tracepoints are not supported by all debugging tools

trap

An interrupt that is generated by the processor's own internal hardware For example, the processor might trap if an illegal opcode is found in your

program Compare with software interrupt

V

volatile

A value that can change without the intervention of software is said to be volatile For example, values within the registers of some I/O devices change

in response to external events C's volatile keyword should be used to warn your compiler about any pointers that point to such registers This will

ensure that the actual value is reread each time the data is used

W

watchdog timer

A hardware timer that is periodically reset by software If the software

crashes or hangs, the watchdog timer will expire, and the entire system will

be reset automatically

Bibliography

One of the most frustrating aspects of developing embedded software is that there are few references available Many of the books that have been written are poor or out of print, and there are only a handful of periodicals dedicated to the subject What follows is an annotated list of the books, magazines, and other resources I found most helpful in writing this book This is not an attempt to itemize all of the relevant publications In fact, I have specifically omitted several books and

magazines that did not impress me What's left is a list of books worth owning, magazines and conferences worthy of your time, and World Wide Web sites worth bookmarking

Books

Ball, Stuart R Embedded Microprocessor Systems: Real World Design Newton,

Mass.: Butterworth-Heinemann, 1996

This tiny book is packed full of information about hardware design and embedded system development that every embedded software engineer should understand to be effective

Brown, John Forrest Embedded Systems Programming in C and Assembly New

York: Van Nostrand Reinhold, 1994

It's a good thing I didn't know about this book a few years ago If I had, I might not have tried writing my own It is obvious to me that Mr Brown and

I had similar visions for our books And since I have tried to stay away from assembly language as much as possible, this book would make an excellent companion to the one you are reading

Ganssle, Jack G The Art of Programming Embedded Systems San Diego:

Academic Press, 1992

Some very practical advice from one of our industry's most vocal gurus The

author of a monthly column in Embedded Systems Programming (described

later in this bibliography), Mr Ganssle has helpfully collected some of his most lasting tips and rules of thumb in this book A handy reference for topics that are too specific to be covered here

Kernighan, Brian W., and Dennis M Ritchie The C Programming Language

Englewood Cliffs, N.J.: Prentice-Hall, 1988

A concise explanation of C's syntax and semantics direct from the founding fathers A necessary component of any programmer's bookshelf

Labrosse, Jean J C/OS: The Real-Time Kernel Lawrence, Kans.: R & D

Publications, 1992

A real-time operating system with source code and explanatory text—all for the price of a book A great investment for someone who's thinking of

writing their own operating system, or just looking for free source code C/OS (pronounced "micro-COS") has been ported to many processors and has a large user base

Rosenberg, Jonathan B How Debuggers Work: Algorithms, Data Structures, and Architecture New York: John P Wiley & Sons, 1996

If you've ever wondered what a debugger looks like on the inside, this book

is for you It will also give you a better understanding of the split between debugger and debug monitor and the potential for interference between the debugger and your programs

Satir, Gregory, and Doug Brown C++: The Core Language Cambridge, Mass.:

O'Reilly & Associates, 1995