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@c  COPYRIGHT (c) 1988-2002.

@c  On-Line Applications Research Corporation (OAR).

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@c  glossary.texi,v 1.7 2002/01/17 21:47:47 joel Exp

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@ifinfo

@node Glossary, Command and Variable Index, Example Application, Top

@end ifinfo

@chapter Glossary

@table @b

@item active

A term used to describe an object

which has been created by an application.

@item aperiodic task

A task which must execute only at

irregular intervals and has only a soft deadline.

@item application

In this document, software which makes

use of RTEMS.

@item ASR

see Asynchronous Signal Routine.

@item asynchronous

Not related in order or timing to

other occurrences in the system.

@item Asynchronous Signal Routine

Similar to a hardware

interrupt except that it is associated with a task and is run in

the context of a task.  The directives provided by the signal

manager are used to service signals.

@item awakened

A term used to describe a task that has

been unblocked and may be scheduled to the CPU.

@item big endian

A data representation scheme in which

the bytes composing a numeric value are arranged such that the

most significant byte is at the lowest address.

@item bit-mapped

A data encoding scheme in which each bit

in a variable is used to represent something different.  This

makes for compact data representation.

@item block

A physically contiguous area of memory.

@item blocked

The task state entered by a task which has

been previously started and cannot continue execution until the

reason for waiting has been satisfied.

@item broadcast

To simultaneously send a message to a

logical set of destinations.

@item BSP

see Board Support Package.

@item Board Support Package

A collection of device

initialization and control routines specific to a particular

type of board or collection of boards.

@item buffer

A fixed length block of memory allocated

from a partition.

@item calling convention

The processor and compiler

dependent rules which define the mechanism used to invoke

subroutines in a high-level language.  These rules define the

passing of arguments, the call and return mechanism, and the

register set which must be preserved.

@item Central Processing Unit

This term is equivalent to

the terms processor and microprocessor.

@item chain

A data structure which allows for efficient

dynamic addition and removal of elements.  It differs from an

array in that it is not limited to a predefined size.

@item coalesce

The process of merging adjacent holes into

a single larger hole.  Sometimes this process is referred to as

garbage collection.

@item Configuration Table

A table which contains

information used to tailor RTEMS for a particular application.

@item context

All of the processor registers and

operating system data structures associated with a task.

@item context switch

Alternate term for task switch.

Taking control of the processor from one task and transferring

it to another task.

@item control block

A data structure used by the

executive to define and control an object.

@item core

When used in this manual, this term refers to

the internal executive utility functions.  In the interest of

application portability, the core of the executive should not be

used directly by applications.

@item CPU

An acronym for Central Processing Unit.

@item critical section

A section of code which must be

executed indivisibly.

@item CRT

An acronym for Cathode Ray Tube.  Normally used

in reference to the man-machine interface.

@item deadline

A fixed time limit by which a task must

have completed a set of actions.  Beyond this point, the results

are of reduced value and may even be considered useless or

harmful.

@item device

A peripheral used by the application that

requires special operation software.  See also device driver.

@item device driver

Control software for special

peripheral devices used by the application.

@item directives

RTEMS' provided routines that provide

support mechanisms for real-time applications.

@item dispatch

The act of loading a task's context onto

the CPU and transferring control of the CPU to that task.

@item dormant

The state entered by a task after it is

created and before it has been started.

@item Device Driver Table

A table which contains the

entry points for each of the configured device drivers.

@item dual-ported

A term used to describe memory which

can be accessed at two different addresses.

@item embedded

An application that is delivered as a

hidden part of a larger system.  For example, the software in a

fuel-injection control system is an embedded application found

in many late-model automobiles.

@item envelope

A buffer provided by the MPCI layer to

RTEMS which is used to pass messages between nodes in a

multiprocessor system.  It typically contains routing

information needed by the MPCI.  The contents of an envelope are

referred to as a packet.

@item entry point

The address at which a function or task

begins to execute.  In C, the entry point of a function is the

function's name.

@item events

A method for task communication and

synchronization. The directives provided by the event manager

are used to service events.

@item exception

A synonym for interrupt.

@item executing

The task state entered by a task after it

has been given control of the CPU.

@item executive

In this document, this term is used to

referred to RTEMS.  Commonly, an executive is a small real-time

operating system used in embedded systems.

@item exported

An object known by all nodes in a

multiprocessor system.  An object created with the GLOBAL

attribute will be exported.

@item external address

The address used to access

dual-ported memory by all the nodes in a system which do not own

the memory.

@item FIFO

An acronym for First In First Out.

@item First In First Out

A discipline for manipulating entries in a data structure.

@item floating point coprocessor

A component used in

computer systems to enhance performance in mathematically

intensive situations.  It is typically viewed as a logical

extension of the primary processor.

@item freed

A resource that has been released by the

application to RTEMS.

@item global

An object that has been created with the

GLOBAL attribute and exported to all nodes in a multiprocessor

system.

@item handler

The equivalent of a manager, except that it

is internal to RTEMS and forms part of the core.  A handler is a

collection of routines which provide a related set of functions.

For example, there is a handler used by RTEMS to manage all

objects.

@item hard real-time system

A real-time system in which a

missed deadline causes the worked performed to have no value or

to result in a catastrophic effect on the integrity of the

system.

@item heap

A data structure used to dynamically allocate

and deallocate variable sized blocks of memory.

@item heterogeneous

A multiprocessor computer system composed of dissimilar processors.

@item homogeneous

A multiprocessor computer system composed of a single type of processor.

@item ID

An RTEMS assigned identification tag used to

access an active object.

@item IDLE task

A special low priority task which assumes

control of the CPU when no other task is able to execute.

@item interface

A specification of the methodology used

to connect multiple independent subsystems.

@item internal address

The address used to access

dual-ported memory by the node which owns the memory.

@item interrupt

A hardware facility that causes the CPU

to suspend execution, save its status, and transfer control to a

specific location.

@item interrupt level

A mask used to by the CPU to

determine which pending interrupts should be serviced.  If a

pending interrupt is below the current interrupt level, then the

CPU does not recognize that interrupt.

@item Interrupt Service Routine

An ISR is invoked by the

CPU to process a pending interrupt.

@item I/O

An acronym for Input/Output.

@item ISR

An acronym for Interrupt Service Routine.

@item kernel

In this document, this term is used as a

synonym for executive.

@item list

A data structure which allows for dynamic

addition and removal of entries.  It is not statically limited

to a particular size.

@item little endian

A data representation scheme in which

the bytes composing a numeric value are arranged such that the

least significant byte is at the lowest address.

@item local

An object which was created with the LOCAL

attribute and is accessible only on the node it was created and

resides upon.  In a single processor configuration, all objects

are local.

@item local operation

The manipulation of an object which

resides on the same node as the calling task.

@item logical address

An address used by an application.

In a system without memory management, logical addresses will

equal physical addresses.

@item loosely-coupled

A multiprocessor configuration

where shared memory is not used for communication.

@item major number

The index of a device driver in the

Device Driver Table.

@item manager

A group of related RTEMS' directives which

provide access and control over resources.

@item memory pool

Used interchangeably with heap.

@item message

A sixteen byte entity used to communicate

between tasks.  Messages are sent to message queues and stored

in message buffers.

@item message buffer

A block of memory used to store

messages.

@item message queue

An RTEMS object used to synchronize

and communicate between tasks by transporting messages between

sending and receiving tasks.

@item Message Queue Control Block

A data structure associated with each message queue used by RTEMS

to manage that message queue.

@item minor number

A numeric value passed to a device

driver, the exact usage of which is driver dependent.

@item mode

An entry in a task's control block that is

used to determine if the task allows preemption, timeslicing,

processing of signals, and the interrupt disable level used by

the task.

@item MPCI

An acronym for Multiprocessor Communications

Interface Layer.

@item multiprocessing

The simultaneous execution of two

or more processes by a multiple processor computer system.

@item multiprocessor

A computer with multiple CPUs

available for executing applications.

@item Multiprocessor Communications Interface Layer

A set

of user-provided routines which enable the nodes in a

multiprocessor system to communicate with one another.

@item Multiprocessor Configuration Table

The data structure defining the characteristics of the multiprocessor

target system with which RTEMS will communicate.

@item multitasking

The alternation of execution amongst a

group of processes on a single CPU.  A scheduling algorithm is

used to determine which process executes at which time.

@item mutual exclusion

A term used to describe the act of

preventing other tasks from accessing a resource simultaneously.

@item nested

A term used to describe an ASR that occurs

during another ASR or an ISR that occurs during another ISR.

@item node

A term used to reference a processor running

RTEMS in a multiprocessor system.

@item non-existent

The state occupied by an uncreated or

deleted task.

@item numeric coprocessor

A component used in computer

systems to enhance performance in mathematically intensive

situations.  It is typically viewed as a logical extension of

the primary processor.

@item object

In this document, this term is used to refer

collectively to tasks, timers, message queues, partitions,

regions, semaphores, ports, and rate monotonic periods.  All

RTEMS objects have IDs and user-assigned names.

@item object-oriented

A term used to describe systems

with common mechanisms for utilizing a variety of entities.

Object-oriented systems shield the application from

implementation details.

@item operating system

The software which controls all

the computer's resources and provides the base upon which

application programs can be written.

@item overhead

The portion of the CPUs processing power

consumed by the operating system.

@item packet

A buffer which contains the messages passed

between nodes in a multiprocessor system.  A packet is the

contents of an envelope.

@item partition

An RTEMS object which is used to allocate

and deallocate fixed size blocks of memory from an dynamically

specified area of memory.

@item Partition Control Block

A data structure associated

with each partition used by RTEMS to manage that partition.

@item pending

A term used to describe a task blocked

waiting for an event, message, semaphore, or signal.

@item periodic task

A task which must execute at regular

intervals and comply with a hard deadline.

@item physical address

The actual hardware address of a

resource.

@item poll

A mechanism used to determine if an event has

occurred by periodically checking for a particular status.

Typical events include arrival of data, completion of an action,

and errors.

@item pool

A collection from which resources are

allocated.

@item portability

A term used to describe the ease with

which software can be rehosted on another computer.

@item posting

The act of sending an event, message,

semaphore, or signal to a task.

@item preempt

The act of forcing a task to relinquish the

processor and dispatching to another task.

@item priority

A mechanism used to represent the relative

importance of an element in a set of items.  RTEMS uses priority

to determine which task should execute.

@item priority inheritance

An algorithm that calls for

the lower priority task holding a resource to have its priority

increased to that of the highest priority task blocked waiting

for that resource.  This avoids the problem of priority

inversion.

@item priority inversion

A form of indefinite

postponement which occurs when a high priority tasks requests

access to shared resource currently allocated to low priority

task.  The high priority task must block until the low priority

task releases the resource.

@item processor utilization

The percentage of processor

time used by a task or a set of tasks.

@item proxy

An RTEMS control structure used to represent,

on a remote node, a task which must block as part of a remote

operation.

@item Proxy Control Block

A data structure associated

with each proxy used by RTEMS to manage that proxy.

@item PTCB

An acronym for Partition Control Block.

@item PXCB

An acronym for Proxy Control Block.

@item quantum

The application defined unit of time in

which the processor is allocated.

@item queue

Alternate term for message queue.

@item QCB

An acronym for Message Queue Control Block.

@item ready

A task occupies this state when it is

available to be given control of the CPU.

@item real-time

A term used to describe systems which are

characterized by requiring deterministic response times to

external stimuli.  The external stimuli require that the

response occur at a precise time or the response is incorrect.

@item reentrant

A term used to describe routines which do

not modify themselves or global variables.

@item region

An RTEMS object which is used to allocate

and deallocate variable size blocks of memory from a dynamically

specified area of memory.

@item Region Control Block

A data structure associated

with each region used by RTEMS to manage that region.

@item registers

Registers are locations physically

located within a component, typically used for device control or

general purpose storage.

@item remote

Any object that does not reside on the local

node.

@item remote operation

The manipulation of an object

which does not reside on the same node as the calling task.

@item return code

Also known as error code or return

value.

@item resource

A hardware or software entity to which

access must be controlled.

@item resume

Removing a task from the suspend state.  If

the task's state is ready following a call to the

@code{@value{DIRPREFIX}task_resume}

directive, then the task is available for scheduling.

@item return code

A value returned by RTEMS directives to

indicate the completion status of the directive.

@item RNCB

An acronym for Region Control Block.

@item round-robin

A task scheduling discipline in which

tasks of equal priority are executed in the order in which they

are made ready.

@item RS-232

A standard for serial communications.

@item running

The state of a rate monotonic timer while

it is being used to delineate a period.  The timer exits this

state by either expiring or being canceled.

@item schedule

The process of choosing which task should

next enter the executing state.

@item schedulable

A set of tasks which can be guaranteed

to meet their deadlines based upon a specific scheduling

algorithm.

@item segments

Variable sized memory blocks allocated

from a region.

@item semaphore

An RTEMS object which is used to

synchronize tasks and provide mutually exclusive access to

resources.

@item Semaphore Control Block

A data structure associated

with each semaphore used by RTEMS to manage that semaphore.

@item shared memory

Memory which is accessible by

multiple nodes in a multiprocessor system.

@item signal

An RTEMS provided mechanism to communicate

asynchronously with a task.  Upon reception of a signal, the ASR

of the receiving task will be invoked.

@item signal set

A thirty-two bit entity which is used to

represent a task's collection of pending signals and the signals

sent to a task.

@item SMCB

An acronym for Semaphore Control Block.

@item soft real-time system

A real-time system in which a

missed deadline does not compromise the integrity of the system.

@item sporadic task

A task which executes at irregular

intervals and must comply with a hard deadline.  A minimum

period of time between successive iterations of the task can be

guaranteed.

@item stack

A data structure that is managed using a Last

In First Out (LIFO) discipline.  Each task has a stack

associated with it which is  used to store return information

and local variables.

@item status code

Also known as error code or return

value.

@item suspend

A term used to describe a task that is not

competing for the CPU because it has had a

@code{@value{DIRPREFIX}task_suspend} directive.

@item synchronous

Related in order or timing to other

occurrences in the system.

@item system call

In this document, this is used as an

alternate term for directive.

@item target

The system on which the application will

ultimately execute.

@item task

A logically complete thread of execution.  The

CPU is allocated among the ready tasks.

@item Task Control Block

A data structure associated with

each task used by RTEMS to manage that task.

@item task switch

Alternate terminology for context

switch.  Taking control of the processor from one task and given

to another.

@item TCB

An acronym for Task Control Block.

@item tick

The basic unit of time used by RTEMS.  It is a

user-configurable number of microseconds.  The current tick

expires when the @code{@value{DIRPREFIX}clock_tick}

directive is invoked.

@item tightly-coupled

A multiprocessor configuration

system which communicates via shared memory.

@item timeout

An argument provided to a number of

directives which determines the maximum length of time an

application task is willing to wait to acquire the resource if

it is not immediately available.

@item timer

An RTEMS object used to invoke subprograms at

a later time.

@item Timer Control Block

A data structure associated

with each timer used by RTEMS to manage that timer.

@item timeslicing

A task scheduling discipline in which

tasks of equal priority are executed for a specific period of

time before being preempted by another task.

@item timeslice

The application defined unit of time in

which the processor is allocated.

@item TMCB

An acronym for Timer Control Block.

@item transient overload

A temporary rise in system

activity which may cause deadlines to be missed.  Rate Monotonic

Scheduling can be used to determine if all deadlines will be met

under transient overload.

@item user extensions

Software routines provided by the

application to enhance the functionality of RTEMS.

@item User Extension Table

A table which contains the

entry points for each user extensions.

@item User Initialization Tasks Table

A table which

contains the information needed to create and start each of the

user initialization tasks.

@item user-provided

Alternate term for user-supplied.

This term is used to designate any software routines which must

be written by the application designer.

@item user-supplied

Alternate term for user-provided.

This term is used to designate any software routines which must

be written by the application designer.

@item vector

Memory pointers used by the processor to

fetch the address of routines which will handle various

exceptions and interrupts.

@item wait queue

The list of tasks blocked pending the

release of a particular resource.  Message queues, regions, and

semaphores have a wait queue associated with them.

@item yield

When a task voluntarily releases control of the processor.

@end table