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 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. 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 (Board Support Package) – 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 80×86 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.
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.
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.
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.
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.
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.
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.
E
EEPROM (Electrically Erasable, Programmable Read-Only Memory) – 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.
embedded system – A combination of computer hardware and software, and perhaps additional mechanical or other parts, designed to perform a dedicated function.
Emulator – A debugging tool that takes the place of or emulates the processor on your target board.
Executable – A file containing object code that is ready for execution on the target.
F
Firmware – Embedded software that is stored as object code within a ROM.
flash memory – A RAM-ROM hybrid that can be erased and rewritten under software control.
G
general-purpose computer – A combination of computer hardware and software that serves as a general-purpose computing platform.
H
HLL – See high-level language.
Heap – An area of memory that is used for dynamic memory allocation.
high-level language – A language, such as C or C++, that is processor-independent.
Host – A general-purpose computer that communicates with the target via a serial port or network connection.
I
ICE – In-Circuit Emulator. See emulator.
I/O – Input/Output. The interface between a processor and the world around it.
I/O device – A piece of hardware that interfaces between the processor and the outside world.
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 space – A special memory region provided by some processors and generally reserved for the attachment of I/O devices.
ISR – See interrupt service routine.
Interrupt – An asynchronous electrical signal from a peripheral to the processor.
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.
intertask communication – A mechanism used by tasks and interrupt service routines to share information and synchronize their access to shared resources.
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.
Locator – A software development tool that assigns physical addresses to the relocatable program produced by the linker.
logic analyzer – A hardware debugging tool that can be used to capture the logic levels of dozens, or even hundreds, of electrical signals in real-time.
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-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.
memory space – A processor’s standard address space.
Microcontroller – A microcontroller is very similar to a microprocessor.
Microprocessor – A piece of silicon containing a general-purpose CPU.
Monitor – In the context of this book, a debug monitor.
Multiprocessing – The use of more than one processor in a single computer system.
Multitasking – The execution of multiple software routines in pseudo-parallel.
Mutex – A data structure for mutual exclusion, also known as a binary semaphore.
mutual exclusion – A guarantee of exclusive access to a shared resource.
N
NVRAM – Non-Volatile Random-Access Memory.
O
OTP – See one-time programmable.
object code – A set of processor-readable opcodes and data.
object file – A file containing object code.
one-time programmable – Any programmable device that can be programmed just once by the end user.
opcode – A sequence of bits that is recognized by the processor as one of the instructions in its instruction set.
operating system – A piece of software that makes multitasking possible.
Oscilloscope – A hardware debugging tool that allows you to view the voltage on one or more electrical lines.
P
PROM – Programmable Read-Only Memory.
parallel processing – The ability to apply two or more processors to a single computation.
Peripheral – A piece of hardware other than the processor, usually memory or an I/O device.
physical address – The actual address that is placed on the address bus when accessing a memory location or register.
Preemptive – A scheduler is said to be preemptive if it allows the running task to be suspended when a higher-priority task becomes ready.
Polling – A method of interfacing with hardware that involves repeatedly reading a status register until the device has reached the awaited state.
Priority – The relative importance of one task compared to another.
priority inversion – An unwanted software situation in which a high-priority task is delayed while waiting for access to a shared resource.
Process – A word that is often confused with task or thread.
Processor – A generic term that does not distinction between microprocessor, microcontroller, and digital signal processor.
processor family – A set of related processors, usually successive generations from the same manufacturer.
processor-independent – A piece of software that is independent of the processor on which it will be run.
processor-specific – A piece of software that is highly dependent on the processor on which it will be run.
Profiler – A software development tool that collects and reports execution statistics for your programs.
program counter – See instruction pointer.
R
RAM – Random-Access Memory.
RISC (Reduced Instruction Set Computer) – Describes the architecture of a processor family.
ROM – Read-Only Memory.
ROM emulator – A debugging tool that takes the place of or emulates the ROM on your target board.
ROM monitor – See debug monitor.
RTOS (Real-Time Operating System) – An operating system designed specifically for use in real-time systems.
race condition – A situation in which the outcome of a program may be affected by the exact order in which the instructions are executed.
real-time system – Any computer system, embedded or otherwise, that has deadlines.
Recursive – Said of software that calls itself.
Reentrant – Said of software that can be executed multiple times simultaneously.
Register – A memory location that is part of a processor or an I/O device.
Relocatable – A file containing object code that is almost ready for execution on the target.
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.
reset vector – See reset address.
S
SRAM (Static Random-Access Memory) – A type of RAM that retains its contents as long as the system is powered on.
Scheduler – The part of an operating system that decides which task to run next.
Semaphore – A data structure that is used for intertask synchronization.
Simulator – A debugging tool that runs on the host and pretends to be the target processor.
software interrupt – An interruption of a program that is initiated by a software instruction.
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.
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.
T
Target – Another name for the embedded system.
Task – The central abstraction of an operating system.
Thread – Another name for a task.
Tracepoint – Like a breakpoint except that a counter is incremented rather than stopping the program.
Trap – An interruption of a program that is triggered by the processor’s own internal hardware.
V
volatile – A value that may change without the intervention of software.
W
watchdog timer – A hardware timer that is periodically reset by software.
END
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