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This article mainly introduces vxworks in real-time what is meant, the text is very detailed, has a certain reference value, interested friends must read!

The so-called "real-time" is a literal translation from Real Time. I think it should be translated as "timely", because real-time system refers to the system's ability to respond to external event requests in a timely manner, complete the processing of the event within a specified time, and control the coordinated operation of related tasks.

Intuitively, real-time systems may feel "fast," but real-time systems are more focused on "quasi," or "deterministic" or "predictable."

For example, operating system A can complete task x in 5 seconds at the fastest, 99% of the time, it will take no more than 8 seconds, but when busy, there is a 1 in 10,000 chance that it will take 20 seconds to complete task x.

OS B takes at most 10 seconds to complete task x, but on busy days it takes at most 12 seconds to complete task x.

In terms of performance, A is more powerful, but in terms of real-time performance, B is higher.

In other words, real-time performance is worse than the worst execution time! Because for real-time systems, just one lateness can be fatal.

Even with the best hardware, it is possible to handle more work than it can handle. The software, the operating system, has to make a trade-off. Different systems adopt different strategies.

The goal of a universal system (such as Windows or desktop Linux) is to satisfy all the needs of all users as much as possible, so in order to handle all the work, it is likely to cause all the work to be delayed.

The real-time system is to ensure that the most important work of the user is completed within a limited time, so important work is prioritized, and unimportant work can only be delayed more. That is, in theory, some jobs in real-time systems may never be processed.

The shorter the limit time that the real-time system can support, the better the real-time performance. Some people put forward the concept of strong real-time and weak real-time according to the length of this limit time. In fact, there is no strict boundary, depending on the specific needs of users.

In addition, if the required work is not completed after the time limit expires, it can be divided into hard real-time and soft real-time according to the severity of the consequence, and there is also no strict limit.

In order to guarantee the limited time and make its behavior "predictable," there is a very important index for real-time systems, that is, the response time should be as short as possible.

This response time is not the execution time consumed to complete the task. Because the length of execution time depends more on the complexity of the task and the performance of the hardware. It refers to the time difference between when a system requirement (which may be an external hardware event or an internal software schedule) is proposed, and when the real-time system drops the work at hand and finally begins to implement this new requirement. That is to say, real-time system is not only to execute fast, but more importantly to respond quickly.

For example, in ordinary Linux, the priority of a process (or thread) only determines the length of its execution time slice, and does not guarantee whether it is executed first. In other words, its execution order is not deterministic and therefore not predictable.

In VxWorks task scheduling, tasks with higher priority will preempt tasks with lower priority. So important work, set it to high priority. This is one of the ways VxWorks works works.

All kinds of operating systems have their own merits, there is no good or bad points, just as Lu Meipo of Song Dynasty said in Xuemei: Mei Xu Xun snow three points white, snow but lose plum a paragraph of incense.

All we have to do is find the best system for the current project. Just like Ruan Yuan of Qing Dynasty said in Wu Xing Miscellaneous Poems: Deep planting water chestnut shallow planting rice, not deep not shallow planting lotus.

How do you determine if an operating system is suitable for your project? Different roles must have different bases. I'll offer you a few points for your information.

Good validation-whether the industry has a large number of success stories;

Reliability-Is the system mature and stable?

Cropability-the system's ability to crop and how to crop

Ease of use-whether it is easy to learn, whether the learning threshold is high, whether the documentation is complete

Technical support-is there localization support and how is it supported?

Processor types supported-whether software and hardware upgrades for subsequent projects are supported

Source code-is it completely safe and controllable

Tools-How easy is it to develop, how is the fault location ability

Price-in line with project budget

In fact, there are many reference factors for the project, and the right to decide is probably not in the hands of one person. Even in many cases, the above factors are not important. Only one condition is considered:

Use whatever Party A asks!

The above is "vxworks real-time is what means" all the content of this article, thank you for reading! Hope to share the content to help everyone, more relevant knowledge, welcome to pay attention to the industry information channel!

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