名词解释_Software_Embedded

名词解释

Posted by: Orest Date: November 24, 2005 01:07PM

AASICApplication-Specific Integrated Circuit. A piece of custom-designed hardware in a chip.address busA set of electrical lines connected to the processor and all of the peripherals with which it communicates. The address bus is used by the processor to select a specific 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. Theapplication software is unlikely to be reusable across embedded platforms, simplybecause each embedded system has a different application.assembler A software development tool that translates human-readable assembly languageprograms into machine-language instructions that the processor can understand and execute.assembly languageA human-readable form of a processor's instruction set. Most processor-specificfunctions must be written in assembly language.

BBSP

See board support package.binary semaphoreA 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 linkedwith the remainder of the software package.bond-out processorA 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 andis never intended to be used in a production system.breakpointA location in a program at which execution is to be stopped and control of theprocessor switched to the debugger. Mechanisms for creating and removingbreakpoints are provided by most debugging tools.

CCISC

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Complex Instruction Set Computer. Describes the architecture of a processorfamily. CISC processors generally feature variable-length instructions, multipleaddressing formats, and contain only a small number of general-purpose registers.Intel's 80x86 family is the quintessential example of CISC. Contrast with RISC.CPUCentral Processing Unit. The part of a processor that executes instructions.compilerA software development tool that translates high-level language programs into the machine-language instructions that a particular processor can understand and execute.contextThe current state of the processor's registers and flags.context switchThe process of switching from one task to another in a multitasking operatingsystem. 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 sectionA block of code that must be executed in sequence and without interruption toguarantee correct operation of the software. See also race condition.cross-compilerA 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.

DDMADirect Memory Access. A technique for transferring data directly between two peripherals (usually memory and an I/O device) with only minimal intervention bythe processor. DMA transfers are managed by a third peripheral called a DMAcontroller.DRAMDynamic 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.

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DSPSee digital signal processor.data busA set of electrical lines connected to the processor and all of the peripherals withwhich it communicates. When the processor wants to read (write) the contents ofa memory location or register within a particular peripheral, it sets the addressbus pins appropriately and receives (transmits) the contents on the data bus.deadlineThe time at which a particular set of computations must be completed. See alsoreal-time system.deadlockAn unwanted software situation in which an entire set of tasks is blocked, waitingfor 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 toprevent deadlocks altogether by following certain software design practices.

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debug monitorA piece of embedded software that has been designed specifically for use as adebugging tool. It usually resides in ROM and communicates with a debugger via aserial port or network connection. The debug monitor provides a set of primitive commands to view and modify memory locations and registers, create and removebreakpoints, and execute your program. The debugger combines these primitivesto fulfill higher-level requests like program download and single-step.debuggerA software development tool used to test and debug embedded software. Thedebugger runs on a host computer and connects to the target through a serial portor network connection. Using a debugger you can download software to the targetfor immediate execution. You can also set breakpoints and examine the contentsof specific memory locations and registers.device driverA software module that hides the details of a particular peripheral and prov

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ides ahigh-level programming interface to it.device programmerA tool for programming non-volatile memories and otherelectrically-programmable devices. Typically, the programmable device is insertedinto a socket on the device programmer and the contents of a memory buffer arethen transferred into it.digital signal processorA 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.

EEEPROMElectrically Erasable, Programmable Read-Only Memory. (Pronounced

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"Double-E"-PROM.) A type of ROM that can be erased electronically.EPROM Erasable, Programmable Read-nly Memory. A type of ROM that can be erased by exposing it to ultraviolet light. Once erased, an EPROM can be reprogrammed withthe help of a device programmer.embedded systemA combination of computer hardware and software, and perhaps additionalmechanical or other parts, designed to perform a dedicated function. In somecases, 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.emulatorShort for In-Circuit Emulator (ICE). A debugging tool that takes the placeof-emulates-the processor on your target board. Emulators frequentlyincorporate 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

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that remains is to place the object code into a ROM or download it via a debugging tool.

FfirmwareEmbedded software that is stored as object code within a ROM. This name is most common among the users of digital signal processors.flash memoryA 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 verylow cost. In some cases, a large flash memory may even be used instead of a disk-drive.

Ggeneral-purpose computerA combination of computer hardware and software that serves as a general-purpose computing platform. For example, a personal computer. Contrastwith embedded system.

HHLLSee high-level language.heapAn 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 languageA 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.hostA 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.

IICEIn-Circuit Emulator. See emulator.I/OInput/Output. The interface between a processor and the world around it. The simplest examples are switches (inputs) and LEDs (outputs).I/O deviceA 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 mapA table or diagram containing the name and address range of each peripheraladdressable by the processor within the I/O space. I/O maps are a helpful aid in getting to know the target.I/O spaceA special memory region provided by some processors and generally reserved f

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or the attachment of I/O devices. Memory locations and registers within an I/Ospace 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 withmemory space.ISRSee interrupt service routine.instruction pointerA register in the processor that contains the address of the next instruction to be executed. Also known as a program counter.interruptAn asynchronous electrical signal from a peripheral to the processor. When theperipheral asserts this signal, we say that an interrupt occurs. When an interruptoccurs, the current state of the processor is saved and an interrupt service routine is executed. When the interrupt service routine exits, control of theprocessor 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 theassociated interrupt service routine.

interrupt service routineA piece of software executed in response to a particular interrupt.interrupt typeA unique number associated with each interrupt.interrupt vectorThe address of an interrupt service routine.interrupt vector tableA table containing interrupt vectors and indexed by interrupt type. This tablecontains the processor's mapping between interrupts and interrupt service routines and must be initialized by the programmer.intertask communicationA mechanism used by tasks and interrupt service routines to share informationand synchronize their access to shared resources. The most common buildingblocks of intertask communication are semaphores and mutexes.

Kkernel

An essential part of any multitasking operating system, the kernel contains just the scheduler and context-switch routine.LlinkerA software development tool that accepts one or more object files as input andoutputs a relocatable program. The linker is thus run after all of the source fileshave been compiled or assembled.locatorA software development tool that assigns physical addresses to the relocatableprogram produced by the linker. This is the last step in the preparation ofsoftware for execution by an embedded system and the resulting file is called anexecutable. In some cases, the locator's function may be hidden within the linker.logic analyzerA hardware debugging tool that can be used to capture the logic levels (0 or 1) ofdozens, or even hundreds, of electrical signals in real-time. Logic analyzers can bequite helpful for debugging hardware problems and complex processor-peripheral

interactions.

Mmemory mapA table or diagram containing the name and address range of each peripheraladdressable by the processor within the memory space. Memory maps are a helpfulaid in getting to know the target.memory-mapped I/OAn increasingly common hardware design methodology in which I/O devices areplaced 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 spaceA processor's standard address space. Contrast with I/O space.microcontrollerA microcontroller is very similar to a microprocessor. The main difference is that a microcontroller is designed specifically for use in embedded systems.Microcontrollers typically include a CPU, memory (a small amount of RAM and/

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or ROM), and other peripherals on the same chip. Common examples are the 8051,Intel's 80196, and Motorola's 68HCxx series.microprocessorA piece of silicon containing a general-purpose CPU. The most common examplesare Intel's 80x86 and Motorola's 680x0 families.monitorIn the context of this book, a debug monitor. However, there is a second meaningfor this word that is associated with intertask communication. In that context, amonitor is a language-level synchronization feature.multiprocessingThe use of more than one processor in a single computer system. So-called"multiprocessor systems" usually have a common memory space through which theprocessors can communicate and share data. In addition, some multiprocessorsystems support parallel processing.multitaskingThe execution of multiple software routines in pseudo-parallel. Each routine represents a separate "thread of execution" and is referred to as a task. The

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operating system is responsible for simulating parallelism by parceling out theprocessor's time.mutexA data structure for mutual exclusion, also known as a binary semaphore. A mutexis basically just a multitasking-aware binary flag that can be used to synchronizethe activities of multiple tasks. As such, it can be used to protect critical sectionsof the code from interruption and shared resources from simultaneous use.mutual exclusionA guarantee of exclusive access to a shared resource. In embedded systems, theshared resource is typically a block of memory, a global variable, or a set ofregisters. Mutual exclusion can be achieved with the use of a semaphore or mutex.

NNVRAMNon-Volatile Random-Access Memory. A type of RAM that retains its data evenwhen the system is powered down. NVRAM frequently consists of an SRAM and a

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long-life battery.OOTPSee one-time programmable.object codeA set of processor-readable opcodes and data. The output of compilers,assemblers, linkers, and locators are files containing object code.object fileA file containing object code. The output of a compiler or assembler.one-time programmableAny programmable device, like a PROM, that can be programmed just once by theend user. However, this term is used almost exclusively to refer to microcontrollers with on-chip PROM.opcodeA sequence of bits that is recognized by the processor as one of the instructionsin its instruction set.operating system

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A piece of software that makes multitasking possible. An operating systemtypically consists of a set of function calls, or software interrupts, and a periodic clock tick. The operating system is responsible for deciding which task should be using the processor at a given time and for controlling access to shared resources.oscilloscopeA hardware debugging tool that allows you to view the voltage on one or more electrical lines. For example, you might use an oscilloscope to determine if a particular interrupt is currently asserted.

PPROMProgrammable Read-Only Memory. A type of ROM that can be written(programmed) with a device programmer. These memory devices can beprogrammed only once, so they are sometimes referred to as write-once orone-time programmable devices.parallel processingThe ability to apply two or more processors to a single computation.

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peripheralA piece of hardware other than the processor, usually memory or an I/O device.The peripheral may reside within the same chip as the processor, in which case itis called an internal peripheral.physical addressThe actual address that is placed on the address bus when accessing a memory location or register.preemptiveA scheduler is said to be preemptive if it allows the running task to be suspendedwhen a higher-priority task becomes ready. Non-preemptive schedulers are easierto implement but less appropriate for embedded systems.pollingA method of interfacing with hardware that involves repeatedly reading a statusregister until the device has reached the awaited state. Device drivers are eitherpolling or interrupt-driven, with the latter being more generally preferred.priority

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The relative importance of one task compared to another.priority inversionAn unwanted software situation in which a high-priority task is delayed whilewaiting for access to a shared resource that is not even being used at the time.For all practical purposes, the priority of this task has been lowered during thedelay period.processA word that is often confused with task or thread. The crucial distinction is that all of the tasks in a system share a common memory space. Processes, on the other hand, always have their own private memory space. Processes are common inmulti-user systems but are rarely, if ever, found in embedded systems.processorA generic term that does not distinguish between microprocessor, microcontroller,and digital signal processor.processor familyA set of related processors, usually successive generations from the same

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manufacturer. For example, Intel's 80x86 family began with the 8086 and nowincludes the 80186, 286, 386, 486, Pentium, and many others. The later models in a family are typically backwards-compatible with the ones that came before.processor-independentA piece of software that is independent of the processor on which it will be run.Most programs that can be written in a high-level language areprocessor-independent. Contrast with processor-specific.processor-specificA piece of software that is highly dependent on the processor on which it will be run. Such code must usually be written in assembly language. Contrast withprocessor-independent.profilerA software development tool that collects and reports execution statistics for your programs. These statistics include the number of calls to each subroutine andthe total amount of time spent within each. This data can be used to learn whichsubroutines are the most critical and, therefore, demand the greatest code efficiency.program counter

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See instruction pointer.

RRAMRandom-Access Memory. A broad classification of memory devices that includes all devices in which individual memory locations may be read or written as required.RISCReduced Instruction Set Computer. Describes the architecture of a processorfamily. RISC processors generally feature fixed-length instructions, a load-storememory architecture, and a large number of general-purpose registers and/orregister windows. The MIPS processor family is an excellent example. Contrastwith CISC.ROMRead-Only Memory. A broad classification of memory devices that includes all devices in which the individual memory locations may be read, but not written.ROM emulatorA debugging tool that takes the place of-or emulates-the ROM on your targetboard. A ROM emulator acts very much like a debug monitor, except that it

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includes its own serial or network connection to the host.ROM monitorSee debug monitor.RTOSReal-Time Operating System. An operating system designed specifically for use inreal-time systems.race conditionA situation in which the outcome of a program may be affected by the exact orderin which the instructions are executed. Race conditions are only an issue whereinterrupts and/or preemption are possible and where critical sections exist.real-time systemAny computer system, embedded or otherwise, that has deadlines. The followingquestion can be used to distinguish real-time systems from the rest: "Is a lateanswer as bad, or even worse, than a wrong answer?" In other words, what happensif the computation doesn't finish in time? If nothing bad happens, it's not a

real-time system. If someone dies or the mission fails, it's generally considered"hard" real-time, which is meant to imply that the system has "hard" deadlines.Everything in between is "soft" real-time.recursiveSaid of software that calls itself. Recursion should generally be avoided in anembedded system, since it frequently requires a large stack.reentrantSaid of software that can be executed multiple times simultaneously. A reentrantfunction can be safely called recursively or from multiple tasks. The key to makingcode reentrant is to ensure mutual exclusion whenever accessing global variablesor shared registers.registerA memory location that is part of a processor or an I/O device. 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
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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 codeA small piece of code that is placed at the reset address. The reset code is usuallywritten in assembly language and may simply be the equivalent of "jump to thestartup code."reset vectorSee reset address.

SSRAMStatic Random-Access Memory. A type of RAM that retains its contents as long as the system is powered on. Data stored in an SRAM is lost when the system is

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powered down or reset.schedulerThe part of an operating system that decides which task to run next. This decisionis based on the readiness of each task, their relative priorities, and the specificscheduling algorithm implemented.semaphoreA data structure that is used for intertask synchronization. Semaphores areusually provided by the operating system.simulatorA 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 embeddedhardware is available. Unfortunately, attempts to simulate interactions withcomplex peripherals are often more trouble than they are worth.software interruptAn interruption of a program that is initiated by a software instruction. Software

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interrupts are commonly used to implement breakpoints and operating systementry points. Unlike true interrupts, they occur synchronously with respect toprogram execution. In other words, software interrupts always occur at thebeginning of an instruction execution cycle. Compare with trap.stackAn area of memory that contains a last-in-first-out queue of storage forparameters, automatic variables, return addresses, and other information thatmust be maintained across function calls. In multitasking situations, each taskgenerally has its own stack.stack frameAn area of the stack associated with a particular function call.startup codeA 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.Ttarget

Another name for the embedded system. This term is usually used during software development, to distinguish the embedded system from the host with which itcommunicates.taskThe 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 eachother's code and data.threadAnother name for a task. This name is more common in operating systems thatsupport processes. A task is simply a thread in a single-process system.tracepointLike a breakpoint except that a counter is incremented rather than stopping the program. Tracepoints are not supported by all debugging tools.trapAn interruption of a program that is triggered by the processor's own internal hardware. For example, the processor might trap if an illegal opcode is foundwithin the program. Compare with software interrupt.

VvolatileA value that may change without the intervention of software is said to be volatile.For example, values within the registers of some I/O devices may change inresponse to external events. C's volatile keyword should be used to warn yourcompiler about any pointers that point to such registers. This will ensure that the actual value is reread each time the data is used.

Wwatchdog timerA 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 resetautomatically.

Edited 1 times. Last edit at 11/24/05 01:12PM by Orest.

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