REAL TIME OPERATING SYSTEM VIVEK JAISWAL 0813331103 EC VI B This template can be used as a starter file to give updates for project milestones. Sections Right-click on a slide to add sections. Sections can help to organize your slides or facilitate collaboration between multiple authors. Notes Use the Notes section for delivery notes or to provide additional details for the audience. View these notes in Presentation View during your presentation. Keep in mind the font size (important for accessibility, visibility, videotaping, and online production) Coordinated colors Pay particular attention to the graphs, charts, and text boxes. Consider that attendees will print in black and white or grayscale. Run a test print to make sure your colors work when printed in pure black and white and grayscale. Graphics, tables, and graphs Keep it simple: If possible, use consistent, non-distracting styles and colors. Label all graphs and tables.

Operating System Collection of system calls (functions) Provides a set of basic services to interact with the hardware Core of the OS is Kernel Basic structural unit of OS Typically a library or set of libraries Operates in supervisory mode What is the project about? Define the goal of this project Is it similar to projects in the past or is it a new effort? Define the scope of this project Is it an independent project or is it related to other projects? * Note that this slide is not necessary for weekly status meetings

Basic Structure of Operating System Application Software Application Programming Interface (API) System Software OS interface OS Hardware OS interface Hardware * If any of these issues caused a schedule delay or need to be discussed further, include details in next slide.

Real Time Operating System A variant of OS Operates in constrained environment where computer memory and processing power is limited Provides services in definite amount of time Duplicate this slide as necessary if there is more than one issue. This and related slides can be moved to the appendix or hidden if necessary.

Features Fast Response times are highly predictable Small and occupy very little memory Consume fewer resources Mission-critical Unpredictable environment Life risking applications

Examples of RTOS

Types of RTOS Hard Real-Time Systems Soft Real-Time Systems It is based on the requirement of meeting the deadline within the time not the length of deadline.

Hard Real-Time Systems Meets deadlines with zero degree of flexibility Missed deadlines cause catastrophe Cost of catastrophe is high

Example of Hard Real-Time Systems Weapons defense system Missile guidance system

Soft Real-Time Systems Meets deadlines with some degree of flexibility Missed deadline does not cause catastrophe Costs rise in proportion to the delay

Example of Soft Real-Time Systems DVD or multimedia players

Scheduling Make 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 Preemptive priority based scheduling algorithm Round Robin scheduling algorithm

Preemptive priority based scheduling algorithm Each task has a priority and highest-priority task runs first

Round Robin scheduling algorithm Each task of same priority uses time slice to achieve equal share of CPU execution time

Tasks An independent thread of execution It is schedulable Characterized by associated name, unique ID, priority, task control block (TCB), stack & task routine Each task moves from one state to another using finite state machine (FSM)

Semaphores A kernel object that one or more threads of execution can acquire or release for the purposes of synchronization or mutual exclusion. Acts like a key Allows a task to carry out some operation or to access a resource Types Binary Semaphore Counting Semaphore Mutual Exclusion Semaphore

Message Queues It is like a pipeline through which tasks & ISRs communicate and synchronize with data.

Ways to use Message Queues Non-interlinked one-way data communication Interlocked two-way data communication Broadcast Communication

Exceptions & Interrupts Exception is any event that disrupts the normal execution of the processor and forces the processor into execution of special instructions Types Synchronous Exceptions Raised by internal events like processor instructions “An arithmetic operation that results in a division by zero” Asynchronous Exceptions Associated with hardware signals from external hardware devices Also called as INTERRUPTS “Pushing the reset button on the embedded board”

Timers & Timer Services It is the scheduling of an event according to a predefined time value in the future. Similar to setting an alarm clock. Types Soft Timer Software events that are scheduled through a software facility Hard Timer Physical timer chips that directly interrupt the processor when they expire

I/O Subsystem 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.

Memory Management Dynamic Memory allocation

Synchronization Resource Synchronization Activity Synchronization Determines whether access to a shared resource is safe and, if not, when it will be safe. Works on client-server model. For instance, one task receives data from sensor & writes it to shared memory, a second task periodically receives data from shared memory and send it to display Determine whether the execution of a multithreaded program has reached a certain state and if it hasn’t, when this state will be reached. Can be either synchronous or asynchronous. For instance, a complex computation can be divided among multiple tasks, some are I/O bound, some are CPU intensive and others are mainly floating point that rely on floating point coprocessors.

Communication Transfer of data from one task to another task. Signal the occurrences of events from one task to another task Control the execution of tasks by other task Synchronize activities Implement additional synchronization protocols for resource sharing

RTOS Distributions QNX RTLinux VxWorks Windows CE OSE freeRTOS

Thank You Prepare slides for the appendix in the event that more details or supplemental slides are needed. The appendix is also useful if the presentation is distributed later.