Operating Systems

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Multi-user systems have two main benefits:

1. The information of different users is kept separate: each can have their own credentials, settings, personal files etc. On Unix-like sytems (Linux, BSD, OS X etc.), each user has their own home directory, generally found at /home/username and referred to as ~/ . This folder contains all data pertaining to that user so that user accounts can, in theory, be moved from one system to another more easily.
2. It is normally more secure; varying privileges can be assigned to different users. This means that users can be prevented from writing to any system files as well as being unable to read or write data belonging to other users on the same system.

1. Procurement function: The first operative function of personnel management is procurement. It is concerned with procuring and employing people who possess necessary skill, knowledge and aptitude. Under its purview you have job analysis, manpower planning, recruitment, selection, placement, induction and internal mobility.

2. Development: It is the process of improving, moulding, changing and developing the skills, knowledge, creative ability, aptitude, attitude, values and commitment based on present and future requirements both at the individual's and organisation's level.

3. Motivation and compensation: It is a process which inspires people to give their best to the organisation through the use of intrinsic (achievement, recognition, responsibility) and extrinsic (job design, work scheduling, appraisal based incentives) rewards.

4. Maintenance: It aims at protecting and preserving the physical and psychological health of employees through various welfare measures.

5. Integration function: This tries to integrate the goals of an organisation with employee aspirations through various employee-oriented programmes, like redressing grievances promptly, instituting proper disciplinary measures, empowering people to decide things independently, encouraging a participative culture, offering constructive help to trade unions etc.

6. Emerging issues: Effective management of human resources depends on refining HRM practices to changing conditions. Hence the need to look at other important issues that can motivate people to give their best in a dynamic and ever-changing environment.

Safe state is one where

• It is not a deadlocked state
• There is some sequence by which all requests can be satisfied.

To avoid deadlocks, we try to make only those transitions that will take you from one safe state to another. We avoid transitions to unsafe state (a state that is not deadlocked, and is not safe)

Multitasking, preemptive, re-entrant kernel

* Supports implementing real-time applications as multiple semi-autonomous tasks. Tasks are always in one of five states: running, ready, blocked, suspended, or delayed.

* Provides for task communication and synchronization, both with other tasks and with interrupt service routines.

Priority Based

* Tasks are implemented as light-weight threads assigned a priority at time of creation.

* Task priorities can be dynamically changed with OsSetTaskPri(). The new priority takes effect immediately. Tasks pending in a priority queue are dynamically re-ordered in the queue.

* A task's priority is temporarily boosted when holding ownership of a mutex being requested by a higher priority task (priority inheritance).

Task Synchronization and Communication

* Semaphores and queues perform either priority or FIFO scheduling of pending tasks. Semaphores are counting semaphores. Message queues have either a fixed maximum size or grow freely, limited only by the amount of available memory.

* Mutexes operate like binary semaphores with ownership and priority inheritance to avoid the problem of priority inversion.

* Events can make multiple tasks ready with a single system call. Events are posted to a nexus which may contain any number of blocked tasks. Tasks waiting for an event use a 32-bit mask to select which events they respond to.

* Timers can be used in a wide variety of system calls. Semaphores, messages, and events can be posted after a fixed delay or posted repeatedly at fixed intervals. Application functions can be called after a fixed delay, or called repeatedly at fixed intervals. Timers can be stopped, tested for expiration, and/or deleted at any time.

Deterministic

* Interrupt latency does not increase as the number of tasks, semaphores, queues, etc., increase.

* The execution time of every service call is independent of the number of tasks, queues, semaphores, etc., in the system, except for the delete and get identifier calls which are infrequent operations.

Responsive

* Timer-related processing that is variant, such as sorting the timer queue, is performed in the background using kernel tasks. Minimal work is performed up front when a system call requires timer processing, allowing the CPU to return more quickly to the application.

Flexible Scheduler

* The scheduler can be configured as non-preemptive, a requirement for some third-party communication protocol stacks. When non-preemptive, running tasks always keep the CPU until making a service call that blocks.

* If configured as preemptive, the scheduler always runs the highest priority ready task. The running task is preempted whenever an interrupt makes ready a task with higher priority than the currently running task.

* Preemption can be temporarily disabled with OsLockTask(). Preemption is re-enabled by either calling OsUnlockTask(), or by making a service call that blocks.

* Tasks may be configured for round robin scheduling among tasks of the same priority. The time slice value is configurable and may be examined or modified at any time.

Easy to Use

* A compile-time option promotes all service call errors to fatal errors that cause an error message on stderr and a break into the debug monitor. This helps catch simple programming errors that can otherwise waste valuable time.

* Kernel objects (tasks, semaphores, queues, mutexes, nexuses, timers) are created dynamically upon request by the application. There is no configuration file to edit and maintain as the application grows. The only limit is the amount of available memory.

Interrupt Service Routine Manager

* isrCreate() creates an entry in the CPU's vector table and installs "wrapper" routines that save and restore the minimal registers required to allow the service routine to be written in C.

* The CPU vector table is initialized at startup with default vectors that allow bus errors and spurious interrupts to be reported on the stderr console.

Command Line Debug Monitor

* Displays the percent of CPU time used by each task and ISR. Displays the stack low water mark for each task. Displays a log of past system calls including the time of the call, the name of the task or ISR making the call, and the values of the parameters used. Allows interactive querying of the state of each task, semaphore, etc.

* Application programs, device drivers, etc. can extend the monitor by adding name strings and code for additional commands.

Integrated Development Environment

* Integrated with TargetToolsâ„¢, the IDE for embedded development from Blunk Microsystems with an integrated compiler and kernel-aware debugger, visual code editor, search and replace tool, BDM for board bring-up, and fast Ethernet download.

Turnkey Solution

* Provided with source code, default compiler settings, linker command files, project files, and a re-entrant Standard C runtime library.

* Blunk Microsystems provides board support packages for a range of commercial CPU boards and provides competitive bids on board support packages for custom designs.

Royalty Free

* Includes source code, User's manual, sample applications, and one year of technical support.