source: rtems/doc/user/glossary.texi @ d4696eb

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2001-01-17 Joel Sherrill <joel@…>

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1@c
2@c  COPYRIGHT (c) 1988-2002.
3@c  On-Line Applications Research Corporation (OAR).
4@c  All rights reserved.
5@c
6@c  $Id$
7@c
8
9@ifinfo
10@node Glossary, Command and Variable Index, Example Application, Top
11@end ifinfo
12@chapter Glossary
13
14@table @b
15@item active
16A term used to describe an object
17which has been created by an application.
18
19@item aperiodic task
20A task which must execute only at
21irregular intervals and has only a soft deadline.
22
23@item application
24In this document, software which makes
25use of RTEMS.
26
27@item ASR
28see Asynchronous Signal Routine.
29
30@item asynchronous
31Not related in order or timing to
32other occurrences in the system.
33
34@item Asynchronous Signal Routine
35Similar to a hardware
36interrupt except that it is associated with a task and is run in
37the context of a task.  The directives provided by the signal
38manager are used to service signals.
39
40@item awakened
41A term used to describe a task that has
42been unblocked and may be scheduled to the CPU.
43
44@item big endian
45A data representation scheme in which
46the bytes composing a numeric value are arranged such that the
47most significant byte is at the lowest address.
48
49@item bit-mapped
50A data encoding scheme in which each bit
51in a variable is used to represent something different.  This
52makes for compact data representation.
53
54@item block
55A physically contiguous area of memory.
56
57@item blocked
58The task state entered by a task which has
59been previously started and cannot continue execution until the
60reason for waiting has been satisfied.
61
62@item broadcast
63To simultaneously send a message to a
64logical set of destinations.
65
66@item BSP
67see Board Support Package.
68
69@item Board Support Package
70A collection of device
71initialization and control routines specific to a particular
72type of board or collection of boards.
73
74@item buffer
75A fixed length block of memory allocated
76from a partition.
77
78@item calling convention
79The processor and compiler
80dependent rules which define the mechanism used to invoke
81subroutines in a high-level language.  These rules define the
82passing of arguments, the call and return mechanism, and the
83register set which must be preserved.
84
85@item Central Processing Unit
86This term is equivalent to
87the terms processor and microprocessor.
88
89@item chain
90A data structure which allows for efficient
91dynamic addition and removal of elements.  It differs from an
92array in that it is not limited to a predefined size.
93
94@item coalesce
95The process of merging adjacent holes into
96a single larger hole.  Sometimes this process is referred to as
97garbage collection.
98
99@item Configuration Table
100A table which contains
101information used to tailor RTEMS for a particular application.
102
103@item context
104All of the processor registers and
105operating system data structures associated with a task.
106
107@item context switch
108Alternate term for task switch.
109Taking control of the processor from one task and transferring
110it to another task.
111
112@item control block
113A data structure used by the
114executive to define and control an object.
115
116@item core
117When used in this manual, this term refers to
118the internal executive utility functions.  In the interest of
119application portability, the core of the executive should not be
120used directly by applications.
121
122@item CPU
123An acronym for Central Processing Unit.
124
125@item critical section
126A section of code which must be
127executed indivisibly.
128
129@item CRT
130An acronym for Cathode Ray Tube.  Normally used
131in reference to the man-machine interface.
132
133@item deadline
134A fixed time limit by which a task must
135have completed a set of actions.  Beyond this point, the results
136are of reduced value and may even be considered useless or
137harmful.
138
139@item device
140A peripheral used by the application that
141requires special operation software.  See also device driver.
142
143@item device driver
144Control software for special
145peripheral devices used by the application.
146
147@item directives
148RTEMS' provided routines that provide
149support mechanisms for real-time applications.
150
151@item dispatch
152The act of loading a task's context onto
153the CPU and transferring control of the CPU to that task.
154
155@item dormant
156The state entered by a task after it is
157created and before it has been started.
158
159@item Device Driver Table
160A table which contains the
161entry points for each of the configured device drivers.
162
163@item dual-ported
164A term used to describe memory which
165can be accessed at two different addresses.
166
167@item embedded
168An application that is delivered as a
169hidden part of a larger system.  For example, the software in a
170fuel-injection control system is an embedded application found
171in many late-model automobiles.
172
173@item envelope
174A buffer provided by the MPCI layer to
175RTEMS which is used to pass messages between nodes in a
176multiprocessor system.  It typically contains routing
177information needed by the MPCI.  The contents of an envelope are
178referred to as a packet.
179
180@item entry point
181The address at which a function or task
182begins to execute.  In C, the entry point of a function is the
183function's name.
184
185@item events
186A method for task communication and
187synchronization. The directives provided by the event manager
188are used to service events.
189
190@item exception
191A synonym for interrupt.
192
193@item executing
194The task state entered by a task after it
195has been given control of the CPU.
196
197@item executive
198In this document, this term is used to
199referred to RTEMS.  Commonly, an executive is a small real-time
200operating system used in embedded systems.
201
202@item exported
203An object known by all nodes in a
204multiprocessor system.  An object created with the GLOBAL
205attribute will be exported.
206
207@item external address
208The address used to access
209dual-ported memory by all the nodes in a system which do not own
210the memory.
211
212@item FIFO
213An acronym for First In First Out.
214
215@item First In First Out
216A discipline for manipulating entries in a data structure.
217
218@item floating point coprocessor
219A component used in
220computer systems to enhance performance in mathematically
221intensive situations.  It is typically viewed as a logical
222extension of the primary processor.
223
224@item freed
225A resource that has been released by the
226application to RTEMS.
227
228@item global
229An object that has been created with the
230GLOBAL attribute and exported to all nodes in a multiprocessor
231system.
232
233@item handler
234The equivalent of a manager, except that it
235is internal to RTEMS and forms part of the core.  A handler is a
236collection of routines which provide a related set of functions.
237For example, there is a handler used by RTEMS to manage all
238objects.
239
240@item hard real-time system
241A real-time system in which a
242missed deadline causes the worked performed to have no value or
243to result in a catastrophic effect on the integrity of the
244system.
245
246@item heap
247A data structure used to dynamically allocate
248and deallocate variable sized blocks of memory.
249
250@item heterogeneous
251A multiprocessor computer system composed of dissimilar processors.
252
253@item homogeneous
254A multiprocessor computer system composed of a single type of processor.
255
256@item ID
257An RTEMS assigned identification tag used to
258access an active object.
259
260@item IDLE task
261A special low priority task which assumes
262control of the CPU when no other task is able to execute.
263
264@item interface
265A specification of the methodology used
266to connect multiple independent subsystems.
267
268@item internal address
269The address used to access
270dual-ported memory by the node which owns the memory.
271
272@item interrupt
273A hardware facility that causes the CPU
274to suspend execution, save its status, and transfer control to a
275specific location.
276
277@item interrupt level
278A mask used to by the CPU to
279determine which pending interrupts should be serviced.  If a
280pending interrupt is below the current interrupt level, then the
281CPU does not recognize that interrupt.
282
283@item Interrupt Service Routine
284An ISR is invoked by the
285CPU to process a pending interrupt.
286
287@item I/O
288An acronym for Input/Output.
289
290@item ISR
291An acronym for Interrupt Service Routine.
292
293@item kernel
294In this document, this term is used as a
295synonym for executive.
296
297@item list
298A data structure which allows for dynamic
299addition and removal of entries.  It is not statically limited
300to a particular size.
301
302@item little endian
303A data representation scheme in which
304the bytes composing a numeric value are arranged such that the
305least significant byte is at the lowest address.
306
307@item local
308An object which was created with the LOCAL
309attribute and is accessible only on the node it was created and
310resides upon.  In a single processor configuration, all objects
311are local.
312
313@item local operation
314The manipulation of an object which
315resides on the same node as the calling task.
316
317@item logical address
318An address used by an application.
319In a system without memory management, logical addresses will
320equal physical addresses.
321
322@item loosely-coupled
323A multiprocessor configuration
324where shared memory is not used for communication.
325
326@item major number
327The index of a device driver in the
328Device Driver Table.
329
330@item manager
331A group of related RTEMS' directives which
332provide access and control over resources.
333
334@item memory pool
335Used interchangeably with heap.
336
337@item message
338A sixteen byte entity used to communicate
339between tasks.  Messages are sent to message queues and stored
340in message buffers.
341
342@item message buffer
343A block of memory used to store
344messages.
345
346@item message queue
347An RTEMS object used to synchronize
348and communicate between tasks by transporting messages between
349sending and receiving tasks.
350
351@item Message Queue Control Block
352A data structure associated with each message queue used by RTEMS
353to manage that message queue.
354
355@item minor number
356A numeric value passed to a device
357driver, the exact usage of which is driver dependent.
358
359@item mode
360An entry in a task's control block that is
361used to determine if the task allows preemption, timeslicing,
362processing of signals, and the interrupt disable level used by
363the task.
364
365@item MPCI
366An acronym for Multiprocessor Communications
367Interface Layer.
368
369@item multiprocessing
370The simultaneous execution of two
371or more processes by a multiple processor computer system.
372
373@item multiprocessor
374A computer with multiple CPUs
375available for executing applications.
376
377@item Multiprocessor Communications Interface Layer
378A set
379of user-provided routines which enable the nodes in a
380multiprocessor system to communicate with one another.
381
382@item Multiprocessor Configuration Table
383The data structure defining the characteristics of the multiprocessor
384target system with which RTEMS will communicate.
385
386@item multitasking
387The alternation of execution amongst a
388group of processes on a single CPU.  A scheduling algorithm is
389used to determine which process executes at which time.
390
391@item mutual exclusion
392A term used to describe the act of
393preventing other tasks from accessing a resource simultaneously.
394
395@item nested
396A term used to describe an ASR that occurs
397during another ASR or an ISR that occurs during another ISR.
398
399@item node
400A term used to reference a processor running
401RTEMS in a multiprocessor system.
402
403@item non-existent
404The state occupied by an uncreated or
405deleted task.
406
407@item numeric coprocessor
408A component used in computer
409systems to enhance performance in mathematically intensive
410situations.  It is typically viewed as a logical extension of
411the primary processor.
412
413@item object
414In this document, this term is used to refer
415collectively to tasks, timers, message queues, partitions,
416regions, semaphores, ports, and rate monotonic periods.  All
417RTEMS objects have IDs and user-assigned names.
418
419@item object-oriented
420A term used to describe systems
421with common mechanisms for utilizing a variety of entities.
422Object-oriented systems shield the application from
423implementation details.
424
425@item operating system
426The software which controls all
427the computer's resources and provides the base upon which
428application programs can be written.
429
430@item overhead
431The portion of the CPUs processing power
432consumed by the operating system.
433
434@item packet
435A buffer which contains the messages passed
436between nodes in a multiprocessor system.  A packet is the
437contents of an envelope.
438
439@item partition
440An RTEMS object which is used to allocate
441and deallocate fixed size blocks of memory from an dynamically
442specified area of memory.
443
444@item Partition Control Block
445A data structure associated
446with each partition used by RTEMS to manage that partition.
447
448@item pending
449A term used to describe a task blocked
450waiting for an event, message, semaphore, or signal.
451
452@item periodic task
453A task which must execute at regular
454intervals and comply with a hard deadline.
455
456@item physical address
457The actual hardware address of a
458resource.
459
460@item poll
461A mechanism used to determine if an event has
462occurred by periodically checking for a particular status.
463Typical events include arrival of data, completion of an action,
464and errors.
465
466@item pool
467A collection from which resources are
468allocated.
469
470@item portability
471A term used to describe the ease with
472which software can be rehosted on another computer.
473
474@item posting
475The act of sending an event, message,
476semaphore, or signal to a task.
477
478@item preempt
479The act of forcing a task to relinquish the
480processor and dispatching to another task.
481
482@item priority
483A mechanism used to represent the relative
484importance of an element in a set of items.  RTEMS uses priority
485to determine which task should execute.
486
487@item priority inheritance
488An algorithm that calls for
489the lower priority task holding a resource to have its priority
490increased to that of the highest priority task blocked waiting
491for that resource.  This avoids the problem of priority
492inversion.
493
494@item priority inversion
495A form of indefinite
496postponement which occurs when a high priority tasks requests
497access to shared resource currently allocated to low priority
498task.  The high priority task must block until the low priority
499task releases the resource.
500
501@item processor utilization
502The percentage of processor
503time used by a task or a set of tasks.
504
505@item proxy
506An RTEMS control structure used to represent,
507on a remote node, a task which must block as part of a remote
508operation.
509
510@item Proxy Control Block
511A data structure associated
512with each proxy used by RTEMS to manage that proxy.
513
514@item PTCB
515An acronym for Partition Control Block.
516
517@item PXCB
518An acronym for Proxy Control Block.
519
520@item quantum
521The application defined unit of time in
522which the processor is allocated.
523
524@item queue
525Alternate term for message queue.
526
527@item QCB
528An acronym for Message Queue Control Block.
529
530@item ready
531A task occupies this state when it is
532available to be given control of the CPU.
533
534@item real-time
535A term used to describe systems which are
536characterized by requiring deterministic response times to
537external stimuli.  The external stimuli require that the
538response occur at a precise time or the response is incorrect.
539
540@item reentrant
541A term used to describe routines which do
542not modify themselves or global variables.
543
544@item region
545An RTEMS object which is used to allocate
546and deallocate variable size blocks of memory from a dynamically
547specified area of memory.
548
549@item Region Control Block
550A data structure associated
551with each region used by RTEMS to manage that region.
552
553@item registers
554Registers are locations physically
555located within a component, typically used for device control or
556general purpose storage.
557
558@item remote
559Any object that does not reside on the local
560node.
561
562@item remote operation
563The manipulation of an object
564which does not reside on the same node as the calling task.
565
566@item return code
567Also known as error code or return
568value.
569
570@item resource
571A hardware or software entity to which
572access must be controlled.
573
574@item resume
575Removing a task from the suspend state.  If
576the task's state is ready following a call to the
577@code{@value{DIRPREFIX}task_resume}
578directive, then the task is available for scheduling.
579
580@item return code
581A value returned by RTEMS directives to
582indicate the completion status of the directive.
583
584@item RNCB
585An acronym for Region Control Block.
586
587@item round-robin
588A task scheduling discipline in which
589tasks of equal priority are executed in the order in which they
590are made ready.
591
592@item RS-232
593A standard for serial communications.
594
595@item running
596The state of a rate monotonic timer while
597it is being used to delineate a period.  The timer exits this
598state by either expiring or being canceled.
599
600@item schedule
601The process of choosing which task should
602next enter the executing state.
603
604@item schedulable
605A set of tasks which can be guaranteed
606to meet their deadlines based upon a specific scheduling
607algorithm.
608
609@item segments
610Variable sized memory blocks allocated
611from a region.
612
613@item semaphore
614An RTEMS object which is used to
615synchronize tasks and provide mutually exclusive access to
616resources.
617
618@item Semaphore Control Block
619A data structure associated
620with each semaphore used by RTEMS to manage that semaphore.
621
622@item shared memory
623Memory which is accessible by
624multiple nodes in a multiprocessor system.
625
626@item signal
627An RTEMS provided mechanism to communicate
628asynchronously with a task.  Upon reception of a signal, the ASR
629of the receiving task will be invoked.
630
631@item signal set
632A thirty-two bit entity which is used to
633represent a task's collection of pending signals and the signals
634sent to a task.
635
636@item SMCB
637An acronym for Semaphore Control Block.
638
639@item soft real-time system
640A real-time system in which a
641missed deadline does not compromise the integrity of the system.
642
643@item sporadic task
644A task which executes at irregular
645intervals and must comply with a hard deadline.  A minimum
646period of time between successive iterations of the task can be
647guaranteed.
648
649@item stack
650A data structure that is managed using a Last
651In First Out (LIFO) discipline.  Each task has a stack
652associated with it which is  used to store return information
653and local variables.
654
655@item status code
656Also known as error code or return
657value.
658
659@item suspend
660A term used to describe a task that is not
661competing for the CPU because it has had a
662@code{@value{DIRPREFIX}task_suspend} directive.
663
664@item synchronous
665Related in order or timing to other
666occurrences in the system.
667
668@item system call
669In this document, this is used as an
670alternate term for directive.
671
672@item target
673The system on which the application will
674ultimately execute.
675
676@item task
677A logically complete thread of execution.  The
678CPU is allocated among the ready tasks.
679
680@item Task Control Block
681A data structure associated with
682each task used by RTEMS to manage that task.
683
684@item task switch
685Alternate terminology for context
686switch.  Taking control of the processor from one task and given
687to another.
688
689@item TCB
690An acronym for Task Control Block.
691
692@item tick
693The basic unit of time used by RTEMS.  It is a
694user-configurable number of microseconds.  The current tick
695expires when the @code{@value{DIRPREFIX}clock_tick}
696directive is invoked.
697
698@item tightly-coupled
699A multiprocessor configuration
700system which communicates via shared memory.
701
702@item timeout
703An argument provided to a number of
704directives which determines the maximum length of time an
705application task is willing to wait to acquire the resource if
706it is not immediately available.
707
708@item timer
709An RTEMS object used to invoke subprograms at
710a later time.
711
712@item Timer Control Block
713A data structure associated
714with each timer used by RTEMS to manage that timer.
715
716@item timeslicing
717A task scheduling discipline in which
718tasks of equal priority are executed for a specific period of
719time before being preempted by another task.
720
721@item timeslice
722The application defined unit of time in
723which the processor is allocated.
724
725@item TMCB
726An acronym for Timer Control Block.
727
728@item transient overload
729A temporary rise in system
730activity which may cause deadlines to be missed.  Rate Monotonic
731Scheduling can be used to determine if all deadlines will be met
732under transient overload.
733
734@item user extensions
735Software routines provided by the
736application to enhance the functionality of RTEMS.
737
738@item User Extension Table
739A table which contains the
740entry points for each user extensions.
741
742@item User Initialization Tasks Table
743A table which
744contains the information needed to create and start each of the
745user initialization tasks.
746
747@item user-provided
748Alternate term for user-supplied.
749This term is used to designate any software routines which must
750be written by the application designer.
751
752@item user-supplied
753Alternate term for user-provided.
754This term is used to designate any software routines which must
755be written by the application designer.
756
757@item vector
758Memory pointers used by the processor to
759fetch the address of routines which will handle various
760exceptions and interrupts.
761
762@item wait queue
763The list of tasks blocked pending the
764release of a particular resource.  Message queues, regions, and
765semaphores have a wait queue associated with them.
766
767@item yield
768When a task voluntarily releases control of the processor.
769
770@end table
771
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