Application-Specific Integrated Circuit. A piece of custom-designed hardware in a chip.
address bus （地址总线）
A set of electrical lines connected to the processor and all of the peripherals withwhich itcommunicates. 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.
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.
A software development tool that translates human-readable assembly languageprograms into machine-language instructions that the processor can understandand execute.
A human-readable form of a processor"s instruction set. Most processor-specific functions must be written in assembly language.
See board support package.
见board support package。
A type of semaphore with just two states. Also called a mutex.
board support package（板卡支持包）
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 （外合处理器）
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.
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.
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.
Central Processing Unit. The part of a processor that executes instructions.
A software development tool that translates high-level language programs into the machine-language instructions that a particular processor can understand and execute.
The current state of the processor"s registers and flags.
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.
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.
A block of code that must be executed in sequence and without interruption to guarantee correct operation of the software. See also race condition.
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.
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.
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.
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.
The time at which a particular set of computations must be completed. See also real-time system.
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.
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.
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.
A software module that hides the details of a particular peripheral and provides a high-level programming interface to it.
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（数字信号处理器）
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.
Electrically Erasable, Programmable Read-Only Memory. (Pronounced"Double-E"-PROM.) A type of ROM that can be erased electronically.
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.
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.
Short for In-Circuit Emulator (ICE). A debugging tool that takes the placeof-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
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.
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 （闪存）
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 fash memory may even be used instead of a disk-drive.
A combination of computer hardware and software that serves as a
general-purpose computing platform. For example, a personal computer. Contrast with embedded system.
See high-level language.
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.
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.
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.
In-Circuit Emulator. See emulator.
Input/Output. The interface between a processor and the world around it. The simplest examples are switches (inputs) and LEDs (outputs).
A piece of hardware that interfaces between the processor and the outside world. Common examples are switches and LEDs, serial ports, and network controllers.
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.
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.
一个由处理器提供的特殊内存区域，一般为为I/O设备的附件保留。在I/O空间的内存位置和寄存器只能通过特殊的指定进行访问。例如：80X86家族的处理器有叫做in / out的特殊的I/O空间指令。相对内存空间而言。
See interrupt service routine.
A register in the processor that contains the address of the next instruction to be executed. Also known as a program counter.
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.
The amount of time between the assertion of an interrupt and the start of the associated interrupt service routine.
interrupt service routine（中断服务程序）
A piece of software executed in response to a particular interrupt.
A unique number associated with each interrupt.
interrupt vector （中断向量）
The address of an interrupt service routine.
interrupt vector table（中断向量表）
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.
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.
An essential part of any multitasking operating system, the kernel contains just the scheduler and context-switch routine.
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.
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.
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.
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.
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.
A processor"s standard address space. Contrast with I/O space.
A 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/or ROM), and other peripherals on the same chip. Common examples are the 8051, Intel"s 80196, and Motorola"s 68HCxx series.
A piece of silicon containing a general-purpose CPU. The most common examples are Intel"s 80x86 and Motorola"s 680x0 families.
In the context of this book, a debug monitor. However, there is a second meaning for this word that is associated with intertask communication. In that context, a monitor is a language-level synchronization feature.
The use of more than one processor in a single computer system. So-called "multiprocessor systems" usually have a common memory space through which the processors can communicate and share data. In addition, some multiprocessor systems support parallel processing.
The execution of multiple software routines in pseudo-parallel. Each routine represents a separate "thread of execution" and is referred to as a task. The operating system is responsible for simulating parallelism by parceling out the processor"s time.
A data structure for mutual exclusion, also known as a binary semaphore. A mutex is basically just a multitasking-aware binary flag that can be used to synchronize the activities of multiple tasks. As such, it can be used to protect critical sections of the code from interruption and shared resources from simultaneous use.
A guarantee of exclusive access to a shared resource. In embedded systems, the shared resource is typically a block of memory, a global variable, or a set of registers. Mutual exclusion can be achieved with the use of a semaphore or mutex.
Non-Volatile Random-Access Memory. A type of RAM that retains its data even when the system is powered down. NVRAM frequently consists of an SRAM and a long-life battery.
See one-time programmable.
A set of processor-readable opcodes and data. The output of compilers,assemblers, linkers, and locators are files containing object code.
A file containing object code. The output of a compiler or assembler.
Any programmable device, like a PROM, that can be programmed just once by the end user. However, this term is used almost exclusively to refer to microcontrollers with on-chip PROM.
A sequence of bits that is recognized by the processor as one of the instructions in its instruction set.
A piece of software that makes multitasking possible. An operating system typically 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.
A 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.
Programmable Read-Only Memory. A type of ROM that can be written (programmed) with a device programmer. These memory devices can be programmed only once, so they are sometimes referred to as write-once or one-time programmable devices.
The ability to apply two or more processors to a single computation.
A 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 it is called an internal peripheral.
The actual address that is placed on the address bus when accessing a memory location or register.
A scheduler is said to be preemptive if it allows the running task to be suspended when a higher-priority task becomes ready. Non-preemptive schedulers are easier to implement but less appropriate for embedded systems.
A method of interfacing with hardware that involves repeatedly reading a status register until the device has reached the awaited state. Device drivers are either polling or interrupt-driven, with the latter being more generally preferred.
The relative importance of one task compared to another.
An unwanted software situation in which a high-priority task is delayed while waiting 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 the delay period.
A 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 in multi-user systems but are rarely, if ever, found in embedded systems.
A generic term that does not distinction between microprocessor, microcontroller, and digital signal processor.
A set of related processors, usually successive generations from the same manufacturer. For example, Intel"s 80x86 family began with the 8086 and now includes 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.
一个相关的处理器集，常常连续地从一个生产商产生。例如：Intel"s 80x86族开始从8086开始，现在有80186, 286, 386, 486, Pentium及其他。在一个族中，稍后的产品典型地向后兼容在它以前生产的产品。
A 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 are processor-independent. Contrast with processor-specific.
A 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 with processor-independent.
A software development tool that collects and reports execution statistics for your programs. These statistics include the number of calls to each subroutine and the total amount of time spent within each. This data can be used to learn which subroutines are the most critical and, therefore, demand the greatest code efficiency.
See instruction pointer.
Random-Access Memory. A broad classification of memory devices that includes all devices in which individual memory locations may be read or written as required.
Reduced Instruction Set Computer. Describes the architecture of a processor family. RISC processors generally feature fixed-length instructions, a load-store memory architecture, and a large number of general-purpose registers and/or register windows. The MIPS processor family is an excellent example. Contrast with CISC.
Read-Only Memory. A broad classification of memory devices that includes all devices in which the individual memory locations may be read, but not written.
A debugging tool that takes the place of-or emulates-the ROM on your target board. A ROM emulator acts very much like a debug monitor, except that it includes its own serial or network connection to the host.
See debug monitor.
Real-Time Operating System. An operating system designed specifically for use in real-time systems.
A situation in which the outcome of a program may be affected by the exact order in which the instructions are executed. Race conditions are only an issue where interrupts and/or preemption are possible and where critical sections exist.
Any computer system, embedded or otherwise, that has deadlines. The following question can be used to distinguish real-time systems from the rest: "Is a late answer as bad, or even worse, than a wrong answer?" In other words, what happens if 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.
Said of software that calls itself. Recursion should generally be avoided in an embedded system, since it frequently requires a large stack.
Said of 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.
A 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.
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.
The address from which the first instruction will be fetched after the processor is powered on or reset.
A small piece of code that is placed at the reset address. The reset code is usually written in assembly language and may simply be the equivalent of "jump to the startup code."
See reset address.
Static 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 powered down or reset.
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.
A data structure that is used for intertask synchronization. Semaphores are usually provided by the operating system.
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.
An interruption of a program that is initiated by a software instruction. Software interrupts are commonly used to implement breakpoints and operating system entry points. Unlike true interrupts, they occur synchronously with respect to program execution. In other words, software interrupts always occur at the beginning of an instruction execution cycle.
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.
An area of the stack associated with a particular function call.
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.
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.
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.
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.
Like a breakpoint except that a counter is incremented rather than stopping the program. Tracepoints are not supported by all debugging tools.
An 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 found within the program. Compare with software interrupt.
A 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 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.
A hardware timer that is periodically reset by software. If the software crashesor hangs, the watchdog timer will expire, and the entire system will be reset automatically.