嵌入式系统词汇表.txt

关于嵌入式开发的词汇表

嵌入式系统词汇表
A
ASIC
Application-Specific Integrated Circuit. A piece of custom-designed hardware in a chip.
address bus 
A set of electrical lines connected to the processor and all of the peripherals withwhich it communicates. The address bus is used by the processor to select aspecific memory location or register within a particular peripheral. If the address bus contains n electrical lines, the processor can uniquely address up to 2^n such locations.
application software
Describes software modules specific to a particular embedded project. The
application software is unlikely to be reusable across embedded platforms, simply
because each embedded system has a different application.
assembler
A software development tool that translates human-readable assembly language
programs into machine-language instructions that the processor can understand
and execute.
assembly language
A human-readable form of a processor's instruction set. Most processor-specific
functions must be written in assembly language.
B
BSP
See board support package.
binary semaphore
A type of semaphore with just two states. Also called a mutex.
board support package
Part of a software package that is processor or platform-dependent. Typically,
sample source code for the board support package is provided by the package
developer. The sample code must be modified as necessary, compiled, and linked
with the remainder of the software package.
bond-out processor
A special version of a processor that has some of the internal signals brought out
to external pins. A bond-out processor is most often found within an emulator and
is never intended to be used in a production system.
breakpoint
A location in a program at which execution is to be stopped and control of the
processor switched to the debugger. Mechanisms for creating and removing
breakpoints are provided by most debugging tools.
C
CISC
Complex Instruction Set Computer. Describes the architecture of a processor
family. CISC processors generally feature variable-length instructions, multiple
addressing formats, and contain only a small number of general-purpose registers.
Intel's 80x86 family is the quintessential example of CISC. Contrast with RISC.
CPU
Central Processing Unit. The part of a processor that executes instructions.

compiler
A software development tool that translates high-level language programs into the
machine-language instructions that a particular processor can understand and execute.
context
The current state of the processor's registers and flags.
context switch
The process of switching from one task to another in a multitasking operating
system. A context switch involves saving the context of the running task and
restoring the previously-saved context of the other. The piece of code that does
this is necessarily processor-specific.
counting semaphore
A type of semaphore that is used to track multiple resources of the same type. An
attempt to take a counting semaphore is blocked only if all of the available
resources are in use. Contrast with binary semaphore.
critical section
A block of code that must be executed in sequence and without interruption to
guarantee correct operation of the software. See also race condition.
cross-compiler
A compiler that runs on a different platform than the one for which it produces
object code. A cross-compiler runs on a host computer and produces object code
for the target.
D
DMA
Direct Memory Access. A technique for transferring data directly between two
peripherals (usually memory and an I/O device) with only minimal intervention by
the processor. DMA transfers are managed by a third peripheral called a DMA controller.
DRAM
Dynamic Random-Access Memory. A type of RAM that maintains its contents only
as long as the data stored in the device is refreshed at regular intervals. 
The refresh cycles are usually performed by a peripheral called a DRAM controller.
DSP
See digital signal processor.
data bus
A set of electrical lines connected to the processor and all of the peripherals with
which it communicates. When the processor wants to read (write) the contents of
a memory location or register within a particular peripheral, it sets the address
bus pins appropriately and receives (transmits) the contents on the data bus. 
deadline
The time at which a particular set of computations must be completed. See also
real-time system.
deadlock
An unwanted software situation in which an entire set of tasks is blocked, waiting
for an event that only a task within the same set can cause. If a deadlock occurs,
the only solution is to reset the hardware. However, it is usually possible to
prevent deadlocks altogether by following certain software design practices.

debug monitor
A piece of embedded software that has been designed specifically for use as a
debugging tool. It usually resides in ROM and communicates with a debugger via a
serial port or network connection. The debug monitor provides a set of primitive
commands to view and modify memory locations and registers, create and remove
breakpoints, and execute your program. The debugger combines these primitives
to fulfill higher-level requests like program download and single-step.
debugger
A software development tool used to test and debug embedded software. The
debugger runs on a host computer and connects to the target through a serial port
or network connection. Using a debugger you can download software to the target
for immediate execution. You can also set breakpoints and examine the contents
of specific memory locations and registers.
device driver
A software module that hides the details of a particular peripheral and provides a
high-level programming interface to it.
device programmer
A tool for programming non-volatile memories and other
electrically-programmable devices. Typically, the programmable device is inserted
into a socket on the device programmer and the contents of a memory buffer are
then transferred into it.
digital signal processor
A device that is similar to a microprocessor, except that the internal CPU has been
optimized for use in applications involving discrete-time signal processing. In
addition to standard microprocessor instructions, DSPs usually support a set of
complex instructions to perform common signal-processing computations quickly.
Common DSP families are TI's 320Cxx and Motorola's 5600x series.
E
EEPROM
Electrically Erasable, Programmable Read-Only Memory. (Pronounced
"Double-E"-PROM.) A type of ROM that can be erased electronically.
EPROM
Erasable, Programmable Read-Only Memory. A type of ROM that can be erased by
exposing it to ultraviolet light. Once erased, an EPROM can be reprogrammed with
the help of a device programmer.
embedded system
A combination of computer hardware and software, and perhaps additional
mechanical or other parts, designed to perform a dedicated function. In some
cases, embedded systems are part of a larger system or product, as is the case of
an anti-lock braking system in a car. Contrast with general-purpose computer. 
emulator
Short for In-Circuit Emulator (ICE). A debugging tool that takes the place
of-emulates-the processor on your target board. Emulators frequently
incorporate a special "bond-out" version of the target processor that allows
 you to observe and record its internal state as your program is executing.
executable
A file containing object code that is ready for execution on the target. All that
remains is to place the object code into a ROM or download it via a debugging tool.
F
firmware
Embedded software that is stored as object code within a ROM. This name is most
common among the users of digital signal processors.
flash memory
A RAM-ROM hybrid that can be erased and rewritten under software control.
Such devices are divided into blocks, called sectors, that are individually-erasable.
Flash memory is common in systems that require nonvolatile data storage at very
low cost. In some cases, a large flash memory may even be used instead of a disk-drive.
G
general-purpose computer
A combination of computer hardware and software that serves as a
general-purpose computing platform. For example, a personal computer. Contrast
with embedded system.
H
HLL
See high-level language.
heap
An area of memory that is used for dynamic memory allocation. Calls to malloc and
free and the C++ operators new and delete result in run-time manipulation of the heap.
high-level language
A language, such as C or C++, that is processor-independent. When programming in
a high-level language, it is possible to concentrate on algorithms and applications
without worrying about the details of a particular processor.
host
A general-purpose computer that communicates with the target via a serial port or
network connection. This term is usually used to distinguish the computer on which
the debugger is running from the embedded system that is being developed.
I
ICE
In-Circuit Emulator. See emulator.
I/O
Input/Output. The interface between a processor and the world around it. The
simplest examples are switches (inputs) and LEDs (outputs).
I/O device
A piece of hardware that interfaces between the processor and the outside world.
Common examples are switches and LEDs, serial ports, and network controllers. 
I/O map
A table or diagram containing the name and address range of each peripheral
addressable by the processor within the I/O space. I/O maps are a helpful aid in
getting to know the target.
I/O space
A special memory region provided by some processors and generally reserved for
the attachment of I/O devices. Memory locations and registers within an I/O
space can be accessed only via special instructions. For example, processors in the
80x86 family have special I/O space instructions called in and out. Contrast with
memory space.
ISR
See interrupt service routine.
instruction pointer
A register in the processor that contains the address of the next instruction to
be executed. Also known as a program counter.
interrupt
An asynchronous electrical signal from a peripheral to the processor. When the
peripheral asserts this signal, we say that an interrupt occurs. When an interrupt
occurs, the current state of the processor is saved and an interrupt service
routine is executed. When the interrupt service routine exits, control of the
processor is returned to whatever part of the software was previously running.
interrupt latency
The amount of time between the assertion of an interrupt and the start of the
associated interrupt service routine.
interrupt service routine
A piece of software executed in response to a particular interrupt.
interrupt type
A unique number associated with each interrupt.
interrupt vector
The address of an interrupt service routine.
interrupt vector table
A table containing interrupt vectors and indexed by interrupt type. This table
contains the processor's mapping between interrupts and interrupt service
routines and must be initialized by the programmer.
intertask communication
A mechanism used by tasks and interrupt service routines to share information
and synchronize their access to shared resources. The most common building
blocks of intertask communication are semaphores and mutexes.
K
kernel
An essential part of any multitasking operating system, the kernel contains just
the scheduler and context-switch routine.
L
linker
A software development tool that accepts one or more object files as input and
outputs a relocatable program. The linker is thus run after all of the source files
have been compiled or assembled.
locator
A software development tool that assigns physical addresses to the relocatable
program produced by the linker. This is the last step in the preparation of
software for execution by an embedded system and the resulting file is called an
executable. In some cases, the locator's function may be hidden within the linker.
logic analyzer
A hardware debugging tool that can be used to capture the logic levels (0 or 1) of
dozens, or even hundreds, of electrical signals in real-time. Logic analyzers can be
quite helpful for debugging hardware problems and complex processor-peripheral
interactions.
M
memory map
A table or diagram containing the name and address range of each peripheral
addressable by the processor within the memory space. Memory maps are a helpful
aid in getting to know the target.
memory-mapped I/O
An increasingly common hardware design methodology in which I/O devices are
placed into the memory space rather than the I/O space. From the processor's
point of view, memory-mapped I/O devices look very much like memory devices.
memory space
A processor's standard address space. Contrast with I/O space.
microcontroller
A microcontroller is very similar to a microprocessor. The main difference is that
a microcontroller is designed specifically for use in embedded systems.