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Questions and Answers
POSIX stands for ______________ Operating System Interface.
POSIX stands for ______________ Operating System Interface.
Portable
The main objective of POSIX is to promote ______________ and portability of application programs across variants of Unix operating systems.
The main objective of POSIX is to promote ______________ and portability of application programs across variants of Unix operating systems.
interoperability
Each process has its own protected ______________ space.
Each process has its own protected ______________ space.
address
A thread is a single flow of execution that runs within a ______________.
A thread is a single flow of execution that runs within a ______________.
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When a process starts to run, it is running a 'ain' thread which is the entry point of a program as the ______________ function in C.
When a process starts to run, it is running a 'ain' thread which is the entry point of a program as the ______________ function in C.
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When a real-time embedded system is built upon an operating system, each task is implemented as a process or simply a single ______________.
When a real-time embedded system is built upon an operating system, each task is implemented as a process or simply a single ______________.
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POSIX and RTOS are related to ______ systems.
POSIX and RTOS are related to ______ systems.
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The minimum profile is used for building small embedded systems without a ______ or a file system.
The minimum profile is used for building small embedded systems without a ______ or a file system.
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The threads running within a ______ share at least the following:
The threads running within a ______ share at least the following:
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The limited profile for embedded systems allows ______ processes and threads.
The limited profile for embedded systems allows ______ processes and threads.
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In the precedence principle, a thread with a higher ______ is always scheduled prior to threads with a lower priority.
In the precedence principle, a thread with a higher ______ is always scheduled prior to threads with a lower priority.
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When a real-time embedded system is built upon an OS, each task is implemented as a ______ or simply as a single thread.
When a real-time embedded system is built upon an OS, each task is implemented as a ______ or simply as a single thread.
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The fairness principle regulates the system's ______ behavior.
The fairness principle regulates the system's ______ behavior.
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For a large (embedded) system consisting of multiple programs, one ______ (starter) program starts all the other programs.
For a large (embedded) system consisting of multiple programs, one ______ (starter) program starts all the other programs.
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The ______() family of functions is a simple, fast implementation without address translation or other MMU services.
The ______() family of functions is a simple, fast implementation without address translation or other MMU services.
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In the preemption principle, a higher-priority thread ______ the execution of the current thread.
In the preemption principle, a higher-priority thread ______ the execution of the current thread.
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The ______() call takes a command, starting up a shell (command language interpreter) to execute the command.
The ______() call takes a command, starting up a shell (command language interpreter) to execute the command.
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Many real-time embedded systems have only ______ resources.
Many real-time embedded systems have only ______ resources.
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A ______ task is a stream of jobs, where the interarrival times between consecutive jobs are almost the same.
A ______ task is a stream of jobs, where the interarrival times between consecutive jobs are almost the same.
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A ______ task is a stream of jobs, where the interarrival times between consecutive jobs may differ widely.
A ______ task is a stream of jobs, where the interarrival times between consecutive jobs may differ widely.
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A ______ task is a stream of jobs, where the interarrival times between consecutive jobs may follow a known probability distribution function.
A ______ task is a stream of jobs, where the interarrival times between consecutive jobs may follow a known probability distribution function.
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A periodic task Ti is specified by a tuple (ri, pi, ei, ______), where ri is the release time.
A periodic task Ti is specified by a tuple (ri, pi, ei, ______), where ri is the release time.
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Many OSs support ______, multiple tasks (threads) compete for the limited computing resources.
Many OSs support ______, multiple tasks (threads) compete for the limited computing resources.
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The ______ principle in task scheduling allows a running task to be interrupted by a higher-priority task.
The ______ principle in task scheduling allows a running task to be interrupted by a higher-priority task.
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Tasks within an OS can generally be classified into: – System ______ and Application Tasks.
Tasks within an OS can generally be classified into: – System ______ and Application Tasks.
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System Tasks, such as the OS kernel ______ and device drivers, offer critical services to Application Tasks.
System Tasks, such as the OS kernel ______ and device drivers, offer critical services to Application Tasks.
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The term “task” is an abstract ______ concept.
The term “task” is an abstract ______ concept.
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For hard real-time systems, – A system responds with bounded response time to external events which are typically associated with hard ______ constraints (deadlines).
For hard real-time systems, – A system responds with bounded response time to external events which are typically associated with hard ______ constraints (deadlines).
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A RTOS may offer many services commonly found in general-purpose OSs, such as – – – – multitasking, ______, task preemption, resource sharing, and intertask communication.
A RTOS may offer many services commonly found in general-purpose OSs, such as – – – – multitasking, ______, task preemption, resource sharing, and intertask communication.
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Based on the precedence and ______ principles, – The purpose of a scheduling policy is to define fairness rules for tasks with the same priority.
Based on the precedence and ______ principles, – The purpose of a scheduling policy is to define fairness rules for tasks with the same priority.
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Study Notes
POSIX
- POSIX stands for "Portable Operating System Interface" and is an open operating system (OS) interface standard.
- The main objective of POSIX is to promote interoperability and portability of application programs across variants of Unix operating systems.
POSIX Processes and Threads
- A process is each executing instance of a program, with its own protected address space.
- A thread is a single flow of execution that runs within a process, with the "main" thread being the entry point of a program.
- A process can create additional threads, making it a collection of one or more threads.
- Four real-time application environment profiles:
- Minimum profile: for small embedded systems without an MMU, file system, or I/O terminal.
- Minimum profile for real-time systems: for building real-time controllers with a file system and I/O terminals.
- Limited profile for embedded systems: for building large embedded systems with no file system.
- Maximum profile: for building large real-time systems and embedded systems with all features supported.
POSIX Real-Time Extensions
- Three principles in priority-based scheduling:
- Precedence principle: higher priority threads are scheduled first.
- Preemption principle: higher priority threads preempt the execution of current threads.
- Fairness principle: regulates scheduling behavior for threads with same or different priorities.
POSIX Process Creation
- fork(): creates a new process that duplicates the calling process.
- exec() family of functions: overlays the calling process image with a new process image.
- posix_spawn() family of functions: a simple, fast implementation without address translation or MMU services.
- system(): starts a shell to execute a command.
Real-Time Tasks
- Periodic tasks: a stream of jobs with almost equal interarrival times.
- Sporadic tasks: a stream of jobs with uneven interarrival times.
- Aperiodic tasks: a stream of jobs with interarrival times following a known probability distribution function.
Task Statics and Dynamics
- Many OSs support multitasking: multiple tasks compete for limited computing resources.
- Tasks within an OS can be classified into:
- System Tasks: offer critical services to Application Tasks.
- Application Tasks: use services provided by System Tasks.
RTOS: Real-Time Operating System
- For hard real-time systems, a system responds with bounded response time to external events with hard timing constraints (deadlines).
- A RTOS may offer many services, including multitasking, priority, task preemption, resource sharing, and intertask communication.
POSIX Real-Time Scheduling Policies
- Based on the precedence and preemption principles, scheduling policies define fairness rules for tasks with the same priority.
- Apply when tasks ready for execution have distinct priorities.
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Description
Quiz on POSIX and RTOS in Operating Systems, covering topics such as POSIX process and thread, real-time extensions, task statics and dynamics, and POSIX real-time scheduling policies. Test your knowledge on the importance of POSIX and its applications in Real-Time Operating Systems.
