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diff --git a/c_user/glossary.rst b/c_user/glossary.rst new file mode 100644 index 0000000..b9d9c7d --- /dev/null +++ b/c_user/glossary.rst @@ -0,0 +1,833 @@ +Glossary +######## + +:dfn:`active` + A term used to describe an object + which has been created by an application. + +:dfn:`aperiodic task` + A task which must execute only at + irregular intervals and has only a soft deadline. + +:dfn:`application` + In this document, software which makes + use of RTEMS. + +:dfn:`ASR` + see Asynchronous Signal Routine. + +:dfn:`asynchronous` + Not related in order or timing to + other occurrences in the system. + +:dfn:`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. + +:dfn:`atomic operations` + Atomic operations are defined in terms of *ISO/IEC 9899:2011*. + +:dfn:`awakened` + A term used to describe a task that has + been unblocked and may be scheduled to the CPU. + +:dfn:`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. + +:dfn:`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. + +:dfn:`block` + A physically contiguous area of memory. + +:dfn:`blocked task` + The task state entered by a task which has been previously started and cannot + continue execution until the reason for waiting has been satisfied. Blocked + tasks are not an element of the set of ready tasks of a scheduler instance. + +:dfn:`broadcast` + To simultaneously send a message to a + logical set of destinations. + +:dfn:`BSP` + see Board Support Package. + +:dfn:`Board Support Package` + A collection of device + initialization and control routines specific to a particular + type of board or collection of boards. + +:dfn:`buffer` + A fixed length block of memory allocated + from a partition. + +:dfn:`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. + +:dfn:`Central Processing Unit` + This term is equivalent to + the terms processor and microprocessor. + +:dfn:`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. + +:dfn:`cluster` + We have clustered scheduling in case the set of processors of a system is + partitioned into non-empty pairwise disjoint subsets. These subsets are called:dfn:`clusters`. Clusters with a cardinality of one are partitions. Each + cluster is owned by exactly one scheduler instance. + +:dfn:`coalesce` + The process of merging adjacent holes into + a single larger hole. Sometimes this process is referred to as + garbage collection. + +:dfn:`Configuration Table` + A table which contains + information used to tailor RTEMS for a particular application. + +:dfn:`context` + All of the processor registers and + operating system data structures associated with a task. + +:dfn:`context switch` + Alternate term for task switch. + Taking control of the processor from one task and transferring + it to another task. + +:dfn:`control block` + A data structure used by the + executive to define and control an object. + +:dfn:`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. + +:dfn:`CPU` + An acronym for Central Processing Unit. + +:dfn:`critical section` + A section of code which must be + executed indivisibly. + +:dfn:`CRT` + An acronym for Cathode Ray Tube. Normally used + in reference to the man-machine interface. + +:dfn:`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. + +:dfn:`device` + A peripheral used by the application that + requires special operation software. See also device driver. + +:dfn:`device driver` + Control software for special + peripheral devices used by the application. + +:dfn:`directives` + RTEMS’ provided routines that provide + support mechanisms for real-time applications. + +:dfn:`dispatch` + The act of loading a task’s context onto + the CPU and transferring control of the CPU to that task. + +:dfn:`dormant` + The state entered by a task after it is + created and before it has been started. + +:dfn:`Device Driver Table` + A table which contains the + entry points for each of the configured device drivers. + +:dfn:`dual-ported` + A term used to describe memory which + can be accessed at two different addresses. + +:dfn:`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. + +:dfn:`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. + +:dfn:`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. + +:dfn:`events` + A method for task communication and + synchronization. The directives provided by the event manager + are used to service events. + +:dfn:`exception` + A synonym for interrupt. + +:dfn:`executing task` + The task state entered by a task after it has been given control of the + processor. On SMP configurations a task may be registered as executing on more + than one processor for short time frames during task migration. Blocked tasks + can be executing until they issue a thread dispatch. + +:dfn:`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. + +:dfn:`exported` + An object known by all nodes in a + multiprocessor system. An object created with the GLOBAL + attribute will be exported. + +:dfn:`external address` + The address used to access + dual-ported memory by all the nodes in a system which do not own + the memory. + +:dfn:`FIFO` + An acronym for First In First Out. + +:dfn:`First In First Out` + A discipline for manipulating entries in a data structure. + +:dfn:`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. + +:dfn:`freed` + A resource that has been released by the + application to RTEMS. + +:dfn:`Giant lock` + The :dfn:`Giant lock` is a recursive SMP lock protecting most parts of the + operating system state. Virtually every operating system service must acquire + and release the Giant lock during its operation. + +:dfn:`global` + An object that has been created with the + GLOBAL attribute and exported to all nodes in a multiprocessor + system. + +:dfn:`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. + +:dfn:`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. + +:dfn:`heap` + A data structure used to dynamically allocate + and deallocate variable sized blocks of memory. + +:dfn:`heir task` + A task is an :dfn:`heir` if it is registered as an heir in a processor of the + system. A task can be the heir on at most one processor in the system. In + case the executing and heir tasks differ on a processor and a thread dispatch + is marked as necessary, then the next thread dispatch will make the heir task + the executing task. + +:dfn:`heterogeneous` + A multiprocessor computer system composed of dissimilar processors. + +:dfn:`homogeneous` + A multiprocessor computer system composed of a single type of processor. + +:dfn:`ID` + An RTEMS assigned identification tag used to + access an active object. + +:dfn:`IDLE task` + A special low priority task which assumes + control of the CPU when no other task is able to execute. + +:dfn:`interface` + A specification of the methodology used + to connect multiple independent subsystems. + +:dfn:`internal address` + The address used to access + dual-ported memory by the node which owns the memory. + +:dfn:`interrupt` + A hardware facility that causes the CPU + to suspend execution, save its status, and transfer control to a + specific location. + +:dfn:`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. + +:dfn:`Interrupt Service Routine` + An ISR is invoked by the + CPU to process a pending interrupt. + +:dfn:`I/O` + An acronym for Input/Output. + +:dfn:`ISR` + An acronym for Interrupt Service Routine. + +:dfn:`kernel` + In this document, this term is used as a + synonym for executive. + +:dfn:`list` + A data structure which allows for dynamic + addition and removal of entries. It is not statically limited + to a particular size. + +:dfn:`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. + +:dfn:`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. + +:dfn:`local operation` + The manipulation of an object which + resides on the same node as the calling task. + +:dfn:`logical address` + An address used by an application. + In a system without memory management, logical addresses will + equal physical addresses. + +:dfn:`loosely-coupled` + A multiprocessor configuration + where shared memory is not used for communication. + +:dfn:`major number` + The index of a device driver in the + Device Driver Table. + +:dfn:`manager` + A group of related RTEMS’ directives which + provide access and control over resources. + +:dfn:`memory pool` + Used interchangeably with heap. + +:dfn:`message` + A sixteen byte entity used to communicate + between tasks. Messages are sent to message queues and stored + in message buffers. + +:dfn:`message buffer` + A block of memory used to store + messages. + +:dfn:`message queue` + An RTEMS object used to synchronize + and communicate between tasks by transporting messages between + sending and receiving tasks. + +:dfn:`Message Queue Control Block` + A data structure associated with each message queue used by RTEMS + to manage that message queue. + +:dfn:`minor number` + A numeric value passed to a device + driver, the exact usage of which is driver dependent. + +:dfn:`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. + +:dfn:`MPCI` + An acronym for Multiprocessor Communications + Interface Layer. + +:dfn:`multiprocessing` + The simultaneous execution of two + or more processes by a multiple processor computer system. + +:dfn:`multiprocessor` + A computer with multiple CPUs + available for executing applications. + +:dfn:`Multiprocessor Communications Interface Layer` + A set + of user-provided routines which enable the nodes in a + multiprocessor system to communicate with one another. + +:dfn:`Multiprocessor Configuration Table` + The data structure defining the characteristics of the multiprocessor + target system with which RTEMS will communicate. + +:dfn:`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. + +:dfn:`mutual exclusion` + A term used to describe the act of + preventing other tasks from accessing a resource simultaneously. + +:dfn:`nested` + A term used to describe an ASR that occurs + during another ASR or an ISR that occurs during another ISR. + +:dfn:`node` + A term used to reference a processor running + RTEMS in a multiprocessor system. + +:dfn:`non-existent` + The state occupied by an uncreated or + deleted task. + +:dfn:`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. + +:dfn:`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. + +:dfn:`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. + +:dfn:`operating system` + The software which controls all + the computer’s resources and provides the base upon which + application programs can be written. + +:dfn:`overhead` + The portion of the CPUs processing power + consumed by the operating system. + +:dfn:`packet` + A buffer which contains the messages passed + between nodes in a multiprocessor system. A packet is the + contents of an envelope. + +:dfn:`partition` + An RTEMS object which is used to allocate + and deallocate fixed size blocks of memory from an dynamically + specified area of memory. + +:dfn:`partition` + Clusters with a cardinality of one are :dfn:`partitions`. + +:dfn:`Partition Control Block` + A data structure associated + with each partition used by RTEMS to manage that partition. + +:dfn:`pending` + A term used to describe a task blocked + waiting for an event, message, semaphore, or signal. + +:dfn:`periodic task` + A task which must execute at regular + intervals and comply with a hard deadline. + +:dfn:`physical address` + The actual hardware address of a + resource. + +:dfn:`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. + +:dfn:`pool` + A collection from which resources are + allocated. + +:dfn:`portability` + A term used to describe the ease with + which software can be rehosted on another computer. + +:dfn:`posting` + The act of sending an event, message, + semaphore, or signal to a task. + +:dfn:`preempt` + The act of forcing a task to relinquish the + processor and dispatching to another task. + +:dfn:`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. + +:dfn:`priority boosting` + A simple approach to extend the priority inheritance protocol for clustered + scheduling is :dfn:`priority boosting`. In case a mutex is owned by a task of + another cluster, then the priority of the owner task is raised to an + artificially high priority, the pseudo-interrupt priority. + +:dfn:`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. + +:dfn:`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. + +:dfn:`processor utilization` + The percentage of processor + time used by a task or a set of tasks. + +:dfn:`proxy` + An RTEMS control structure used to represent, + on a remote node, a task which must block as part of a remote + operation. + +:dfn:`Proxy Control Block` + A data structure associated + with each proxy used by RTEMS to manage that proxy. + +:dfn:`PTCB` + An acronym for Partition Control Block. + +:dfn:`PXCB` + An acronym for Proxy Control Block. + +:dfn:`quantum` + The application defined unit of time in + which the processor is allocated. + +:dfn:`queue` + Alternate term for message queue. + +:dfn:`QCB` + An acronym for Message Queue Control Block. + +:dfn:`ready task` + A task occupies this state when it is available to be given control of a + processor. A ready task has no processor assigned. The scheduler decided that + other tasks are currently more important. A task that is ready to execute and + has a processor assigned is called scheduled. + +:dfn:`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. + +:dfn:`reentrant` + A term used to describe routines which do + not modify themselves or global variables. + +:dfn:`region` + An RTEMS object which is used to allocate + and deallocate variable size blocks of memory from a dynamically + specified area of memory. + +:dfn:`Region Control Block` + A data structure associated + with each region used by RTEMS to manage that region. + +:dfn:`registers` + Registers are locations physically + located within a component, typically used for device control or + general purpose storage. + +:dfn:`remote` + Any object that does not reside on the local + node. + +:dfn:`remote operation` + The manipulation of an object + which does not reside on the same node as the calling task. + +:dfn:`return code` + Also known as error code or return + value. + +:dfn:`resource` + A hardware or software entity to which + access must be controlled. + +:dfn:`resume` + Removing a task from the suspend state. If + the task’s state is ready following a call to the ``rtems_task_resume`` + directive, then the task is available for scheduling. + +:dfn:`return code` + A value returned by RTEMS directives to + indicate the completion status of the directive. + +:dfn:`RNCB` + An acronym for Region Control Block. + +:dfn:`round-robin` + A task scheduling discipline in which + tasks of equal priority are executed in the order in which they + are made ready. + +:dfn:`RS-232` + A standard for serial communications. + +:dfn:`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. + +:dfn:`schedulable` + A set of tasks which can be guaranteed + to meet their deadlines based upon a specific scheduling + algorithm. + +:dfn:`schedule` + The process of choosing which task should + next enter the executing state. + +:dfn:`scheduled task` + A task is :dfn:`scheduled` if it is allowed to execute and has a processor + assigned. Such a task executes currently on a processor or is about to start + execution. A task about to start execution it is an heir task on exactly one + processor in the system. + +:dfn:`scheduler` + A :dfn:`scheduler` or :dfn:`scheduling algorithm` allocates processors to a + subset of its set of ready tasks. So it manages access to the processor + resource. Various algorithms exist to choose the tasks allowed to use a + processor out of the set of ready tasks. One method is to assign each task a + priority number and assign the tasks with the lowest priority number to one + processor of the set of processors owned by a scheduler instance. + +:dfn:`scheduler instance` + A :dfn:`scheduler instance` is a scheduling algorithm with a corresponding + context to store its internal state. Each processor in the system is owned by + at most one scheduler instance. The processor to scheduler instance assignment + is determined at application configuration time. See `Configuring a System`_. + +:dfn:`segments` + Variable sized memory blocks allocated + from a region. + +:dfn:`semaphore` + An RTEMS object which is used to + synchronize tasks and provide mutually exclusive access to + resources. + +:dfn:`Semaphore Control Block` + A data structure associated + with each semaphore used by RTEMS to manage that semaphore. + +:dfn:`shared memory` + Memory which is accessible by + multiple nodes in a multiprocessor system. + +:dfn:`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. + +:dfn:`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. + +:dfn:`SMCB` + An acronym for Semaphore Control Block. + +:dfn:`SMP locks` + The :dfn:`SMP locks` ensure mutual exclusion on the lowest level and are a + replacement for the sections of disabled interrupts. Interrupts are usually + disabled while holding an SMP lock. They are implemented using atomic + operations. Currently a ticket lock is used in RTEMS. + +:dfn:`SMP barriers` + The :dfn:`SMP barriers` ensure that a defined set of independent threads of + execution on a set of processors reaches a common synchronization point in + time. They are implemented using atomic operations. Currently a sense barrier + is used in RTEMS. + +:dfn:`soft real-time system` + A real-time system in which a + missed deadline does not compromise the integrity of the system. + +:dfn:`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. + +:dfn:`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. + +:dfn:`status code` + Also known as error code or return + value. + +:dfn:`suspend` + A term used to describe a task that is not + competing for the CPU because it has had a ``rtems_task_suspend`` directive. + +:dfn:`synchronous` + Related in order or timing to other + occurrences in the system. + +:dfn:`system call` + In this document, this is used as an + alternate term for directive. + +:dfn:`target` + The system on which the application will + ultimately execute. + +:dfn:`task` + A logically complete thread of execution. It consists normally of a set of + registers and a stack. The terms :dfn:`task` and :dfn:`thread` are synonym in + RTEMS. The scheduler assigns processors to a subset of the ready tasks. + +:dfn:`Task Control Block` + A data structure associated with + each task used by RTEMS to manage that task. + +:dfn:`task migration` + :dfn:`Task migration` happens in case a task stops execution on one processor + and resumes execution on another processor. + +:dfn:`task processor affinity` + The set of processors on which a task is allowed to execute. + +:dfn:`task switch` + Alternate terminology for context + switch. Taking control of the processor from one task and given + to another. + +:dfn:`TCB` + An acronym for Task Control Block. + +:dfn:`thread dispatch` + The :dfn:`thread dispatch` transfers control of the processor from the currently + executing thread to the heir thread of the processor. + +:dfn:`tick` + The basic unit of time used by RTEMS. It is a + user-configurable number of microseconds. The current tick + expires when the ``rtems_clock_tick`` + directive is invoked. + +:dfn:`tightly-coupled` + A multiprocessor configuration + system which communicates via shared memory. + +:dfn:`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. + +:dfn:`timer` + An RTEMS object used to invoke subprograms at + a later time. + +:dfn:`Timer Control Block` + A data structure associated + with each timer used by RTEMS to manage that timer. + +:dfn:`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. + +:dfn:`timeslice` + The application defined unit of time in + which the processor is allocated. + +:dfn:`TMCB` + An acronym for Timer Control Block. + +:dfn:`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. + +:dfn:`user extensions` + Software routines provided by the + application to enhance the functionality of RTEMS. + +:dfn:`User Extension Table` + A table which contains the + entry points for each user extensions. + +:dfn:`User Initialization Tasks Table` + A table which + contains the information needed to create and start each of the + user initialization tasks. + +:dfn:`user-provided` + Alternate term for user-supplied. + This term is used to designate any software routines which must + be written by the application designer. + +:dfn:`user-supplied` + Alternate term for user-provided. + This term is used to designate any software routines which must + be written by the application designer. + +:dfn:`vector` + Memory pointers used by the processor to + fetch the address of routines which will handle various + exceptions and interrupts. + +:dfn:`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. + +:dfn:`yield` + When a task voluntarily releases control of the processor. + |