What is the difference between linux and rtos

The difference between linux and rtos: rtos is a real-time operating system, a multi-tasking, thread priority, and multiple interrupt level system that can respond quickly within a specified time; while linux is a time-sharing operation A system is an operating system that can have multiple users. Linux can also be modified into a real-time system by configuring the kernel.

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

What is the difference between linux and rtos

RTOS is a real-time operating system; Linux is a time-sharing system, but it can be changed to a real-time system by configuring the kernel

Real-time operating system

The English name is Real Time Operating System, or RTOS for short.

1. Definition of real-time operating system

Real-time operating system (RTOS) refers to a system that can accept and process data at a fast enough speed when external events or data are generated. , the processing results can control the production process or respond quickly to the processing system within a specified time, and control the operating system that all real-time tasks run in a coordinated manner. Therefore, providing timely response and high reliability are its main features. Real-time operating systems are divided into hard real-time and soft real-time. Hard real-time requires that the operation must be completed within a specified time, which is guaranteed during the design of the operating system; soft real-time only needs to complete the operation as quickly as possible according to the priority of the task. That’s it. The operating system we usually use can become a real-time operating system after certain changes.

A real-time operating system is an operating system that guarantees the completion of specific functions within a certain time limit. For example, an operating system can be designed to ensure that a robot on a production line can access an object. In a "hard" real-time operating system, if the calculations to make the object reachable cannot be completed within the allowed time, the operating system will terminate with an error. In a "soft" real-time operating system, the production line can still continue to work, but the output of the product will be slowed down because the product cannot arrive within the allowed time, which causes the robot to have a short period of non-production. Some real-time operating systems are designed for specific applications, others are general-purpose. Some general purpose operating systems call themselves real-time operating systems. But to some extent, most general-purpose operating systems, such as Microsoft's Windows NT or IBM's OS/390, have real-time system characteristics. That is, even if an operating system is not strictly a real-time system, they can solve some real-time application problems.

2. Characteristics of real-time operating systems

1) Multi-tasking;

2) Thread priority

3) Multiple interrupt levels

Small embedded operating systems often require real-time operating systems, and the kernel must meet the requirements of real-time operating systems.

　3. Related concepts of real-time operating system

　(1) Basic concepts

Code critical section: refers to the code that is indivisible during processing. Once this part of the code starts executing, no interrupt is allowed;

Resource: any entity occupied by the task;

Shared resource: a resource that can be used by more than one task;

Task: also called a thread, is a simple program. Each task is given a certain priority, has its own set of CPU registers and its own stack space. Typically, each task is an infinite loop, and each task is in the following five states: sleeping state, ready state, running state, suspended state, and interrupted state;

Task switching : Save the current status of the running task (all contents in the CPU register) in the task's own stack area, then reload the current status of the next task to be run from the task's stack into the CPU's register, and start Running of the next task;

Kernel: Responsible for managing each task, allocating CPU time to each task, and responsible for communication between tasks. Divided into non-preemptible cores and preemptible cores;

Scheduling: One of the main responsibilities of the kernel is to decide which task's turn to run. Generally based on the priority scheduling method;

　(2) Issues about priority

Task priority: divided into static priority whose priority cannot be changed and dynamic priority whose priority can be changed ；

Priority inversion: The priority inversion problem is the most common problem in real-time systems. The allocation of shared resources can cause low-priority tasks to run first and high-priority tasks to run later. The solution is to use a "priority inheritance" algorithm to temporarily change task priorities to curb priority inversion.

　(3) Mutual exclusion

Although the shared data area simplifies the exchange of information between tasks, the exclusivity of each task must be guaranteed when processing shared data. The general methods to satisfy mutual exclusion conditions include: turning off interrupts, using test and set instructions (TAS), prohibiting task switching, and using semaphores.

Because the significance of using a real-time operating system is to be able to handle various unexpected events in a timely manner, that is, to handle various interrupts, the most important and representative performance index parameters for measuring the embedded real-time operating system are It should undoubtedly be the interrupt response time. Interrupt response time is usually defined as:

Interrupt response time = interrupt delay time, time to save the CPU state, execution time of the ISR of the kernel entering the function [2].

Interrupt delay time = MAX (maximum time to turn off interrupts, maximum instruction time) The time to start executing the first instruction of the ISR [2].

Time-sharing Operating System

English: Time-sharing Operating System

Definition: Make a computer serve several, dozens or even An operating system serving hundreds of users. By connecting the computer to many end users, the time-sharing operating system switches the system processor time and memory space to the programs of each end user in turn at certain intervals. Because the time intervals are short, each user feels as if he has the computer to himself. The characteristic of time-sharing operating system is that it can effectively increase resource utilization. For example, UNIX systems use deprived dynamic priority CPU scheduling to effectively support time-sharing operations.

The time-sharing system is a new type of OS formed to meet user needs. There is a completely different performance difference between it and the multi-channel batch processing system. The needs of users are specifically reflected in the following aspects: Human-computer interaction shared host facilitates users to get on the computer

The basic idea of ​​time-sharing system

Time slice: It is to The computer's system resources (especially CPU time) are divided in time. Each time period is called a time slice, and each user takes turns using the time slice.

Time-sharing technology: Divide the running time of the processor into very short time slices, and allocate the processor to each online job in turn according to the time slice.

Time-sharing operating system: It is an online multi-user interactive operating system. Generally, time slice rotation is used to enable one computer to serve multiple terminals. Ensure fast enough response time for each user and provide interactive session capabilities.

Design goals: Respond to user requests in a timely manner and maximize the utilization of system resources where possible.

Working method:

A host is connected to several terminals; each terminal is used by a user; interactively makes command requests to the system; the system accepts commands from each user; The time slice rotation method is used to process service requests; the results are displayed to the user on the terminal through interaction; the user issues the next command based on the previous step result

The key issue in the implementation of the time-sharing system: timely reception. Deal with it promptly.

Features:

Interactivity: Users engage in human-computer dialogue with the system.

Multi-pathing: Multiple users use the same CPU on their respective terminals at the same time.

Independence: Users can operate independently of each other without interfering with or confusing each other.

Timeliness: Users can get timely answers from the system in a short period of time.

Factors that affect the response time: the number of terminals, the size of the time slice, the amount of information exchange, and the speed of information exchange.

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