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Real Time Operating System
REAL TIME OPERATING SYSTEM<br />VIVEK JAISWAL<br />0813331103<br />EC VI B<br />
Operating System<br /><ul><li>Collection of system calls (functions)</li></ul>Provides a set of basic services to interact with the hardware<br /><ul><li>Core of the OS is Kernel</li></ul>Basic structural unit of OS<br />Typically a library or set of libraries<br /> A bridge between applications and the actual data processing done <br />at the hardware level<br />
Heart Pacemaker</li></li></ul><li>Types of RTOS<br /><ul><li>Hard Real-Time Systems</li></ul>Meets deadlines with zero degree of flexibility<br /> Missed deadlines cause catastrophe<br /> Cost of catastrophe is high<br /><ul><li>Soft Real-Time Systems</li></ul>Meets deadlines with some degree of flexibility<br /> Missed deadline does not cause catastrophe<br /> Costs rise in proportion to the delay<br />
Example of Hard Real-Time Systems<br /><ul><li>Weapons defense system
Waiting Blocked by time</li></li></ul><li>Scheduler<br /><ul><li>Maintains ranked list of tasks based on priority
Makes sure that all tasks meet their timing constraints
It is not a task but a function call [schedule()]
Called at various scheduling points likewise end of ISR, when tasks go to sleep or when they are ready to run
Types of algorithms</li></ul>Preemptive priority based scheduling algorithm<br />Round Robin scheduling algorithm<br />
Preemptive priority based scheduling algorithm<br /><ul><li>Each task has a priority and highest-priority task runs first</li></li></ul><li>Round Robin scheduling algorithm<br /><ul><li>Each task of same priority uses time slice to achieve equal share of CPU execution time</li></li></ul><li>Semaphores<br /><ul><li>A kernel object that one or more threads of execution can acquire or release for the purposes of synchronization or mutual exclusion.
Mutual Exclusion Semaphore</li></li></ul><li>Message Queues<br /><ul><li>It is like a pipeline through which tasks & ISRs communicate and synchronize with data.</li></li></ul><li><ul><li>Non-interlinked </li></ul> one-way data communication<br /><ul><li>Interlocked</li></ul> one-way data communication<br /><ul><li>Interlocked</li></ul> two-way data communication<br /><ul><li>Broadcast Communication</li></ul>Ways to use Message Queues<br />
Exceptions & Interrupts<br /><ul><li>Exception is any event that disrupts the normal execution of the processor and forces the processor into execution of special instructions
Types </li></ul>Synchronous Exceptions Raised by internal events like processor instructions<br /> “An arithmetic operation that results in a division by zero” <br />Asynchronous Exceptions Associated with hardware signals from external hardware devices<br /> Also called as INTERRUPTS<br />“Pushing the reset button on the embedded board”<br />
I/O Subsystem<br /><ul><li>Hides the device-specific information from the kernel as well as from the application developer and to provide a uniform access method to the peripheral I/O devices of the system.
Defines the standard set of functions called API.</li></li></ul><li>Communication<br /><ul><li>Transfer of data from one task to another task.
Signal the occurrences of events from one task to another task